Hopi is answering right now. Last checked 3 min ago. It exposes 195 tools.
Free UK calculators, converters and validators (tax, VAT, stamp duty, dates, units), read-only.
Uptime history
33 hours of history · worst hour 0%
33 hours agonow
95.6%
Uptime 24h
87 of 91 checks
195
Tools
read from the server
219 ms
Response time
average over 24h
open, no key
Access
streamable-http
What the code does
We have not read this server's code yet · tools taken from the live server
Evidence
Things with no honest explanation: a promise that contradicts the code, code that runs at install time while hiding what it does, data leaving the machine.
Claims read-only, but ships mutating tools
hopi_remove_duplicate_lines, hopi_remove_extra_spaces, hopi_remove_line_breaks
заявлено «только чтение», но есть hopi_remove_duplicate_lines
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We found things in this code
Code changes quietly between releases, and nobody reads the diff of a dependency. We do, on every release — watch Hopi and you get told the day something new turns up.
Connect this server
Endpoint below is the one we actually reach during checks — not the one copied from a README. Last verified 3 min ago.
run in your terminal
claude mcp add hopi --transport http https://mcp.hopi.co.uk/mcp~/Library/Application Support/Claude/claude_desktop_config.json
{
"mcpServers": {
"hopi": {
"url": "https://mcp.hopi.co.uk/mcp"
}
}
}~/.codex/config.toml
[mcp_servers.hopi]
url = "https://mcp.hopi.co.uk/mcp".cursor/mcp.json
{
"mcpServers": {
"hopi": {
"url": "https://mcp.hopi.co.uk/mcp"
}
}
}.vscode/mcp.json
{
"mcpServers": {
"hopi": {
"url": "https://mcp.hopi.co.uk/mcp"
}
}
}Available tools 195
Read directly from the server with tools/list, grouped by what they act on.
If a tool disappears, we record the date.
hopi
hopi_add_working_days
Add or subtract a number of working days (Monday to Friday) from a start date, optionally skipping England and Wales bank holidays. Dates use the YYYY-MM-DD format. Bank holiday data covers 2026 and 2027 only, so outside those years just weekends are skipped. Source: https://hopi.co.uk/add-working-days/
hopi_age_calculator
Work out an exact age from a date of birth, as of today or an optional 'as of' date. Dates use the YYYY-MM-DD format. Returns the age in years, months and days, the total days lived, and the next birthday. Source: https://hopi.co.uk/age-calculator/
hopi_alcohol_unit_calculator
Work out UK alcohol units in a drink from its ABV (percentage) and volume (millilitres), using units = ABV x ml / 1000. Optionally give the number of those drinks per week to get a weekly total compared against the NHS low risk guideline of 14 units a week. Source: https://hopi.co.uk/alcohol-unit-calculator/
hopi_alphabetical_order
Sort the lines of a block of text into alphabetical order. Blank lines are dropped. Uses natural en-GB ordering so numbers within lines sort sensibly. Can sort ascending (A to Z) or descending (Z to A), and can ignore case. Source: https://hopi.co.uk/alphabetical-order/
hopi_angle_converter
Convert an angle from one unit to another. Units: deg (degrees), rad (radians), grad (gradians), turn (full turns). Source: https://hopi.co.uk/angle-converter/
hopi_area_converter
Convert an area from one unit to another. Units: sqm (square metres), sqft (square feet), sqyd (square yards), acre (acres), ha (hectares), sqkm (square kilometres), sqmi (square miles). Source: https://hopi.co.uk/area-converter/
hopi_aspect_ratio_calculator
Aspect ratio helper. In 'simplify' mode, give width and height to get the simplified W:H ratio, decimal ratio and nearest common ratio. In 'solve' mode, give a ratio (ratioW:ratioH) plus one of width or height to get the missing side. Source: https://hopi.co.uk/aspect-ratio-calculator/
hopi_average_calculator
Work out the mean, median, mode, sum, count, minimum and maximum of a list of numbers. Provide the numbers separated by spaces, commas, semicolons or new lines (type 1200 rather than 1,200, as commas are treated as separators). Source: https://hopi.co.uk/average-calculator/
hopi_base32_encoder
Encode text to RFC 4648 Base32 or decode Base32 back to text. Encoding maps the UTF-8 bytes of the text into 5-bit groups using the alphabet A to Z then 2 to 7, padded to a multiple of 8 characters with equals signs. Decoding tolerates lowercase input and missing padding, and reports characters outside the alphabet as an error. Source: https://hopi.co.uk/base32-encoder/
hopi_base64
Encode text to Base64, or decode a Base64 string back to text. UTF-8 safe, so accents and emoji survive the round trip. Returns the converted text or a clear error. Source: https://hopi.co.uk/base64/
hopi_bill_splitter
Split a restaurant bill between people. In 'itemised' mode, list each item with its amount and who shared it, then add an optional tip and service charge (both percentages applied to each person's own share). In 'even' mode, split one total evenly with an optional tip. Amounts in GBP. Source: https://hopi.co.uk/bill-splitter/
hopi_bingo_card_generator
Generate one or more UK 90-ball bingo cards. Each card is a 3-row by 9-column grid holding 15 numbers, 5 per row, with each column drawing from its own decade (1 to 9, 10 to 19, and so on up to 80 to 90). Blank squares are null. Source: https://hopi.co.uk/bingo-card-generator/
hopi_bitcoin_address_validator
Check whether a Bitcoin address is valid by verifying its checksum and structure. Supports legacy Base58Check (P2PKH, P2SH) and Bech32/Bech32m SegWit and Taproot addresses, on mainnet and testnet. Does not query the blockchain or check balances. Source: https://hopi.co.uk/bitcoin-address-validator/
hopi_bmi_calculator
Work out body mass index (BMI) from height and weight, with the NHS weight category. Use units 'metric' with heightCm and weightKg, or 'imperial' with heightInches and weightPounds. BMI = weight in kg / (height in metres squared). Source: https://hopi.co.uk/bmi-calculator/
hopi_body_fat_calculator
Estimate body fat percentage using the US Navy tape method from a few measurements. For males give height, neck and waist; for females give height, neck, waist and hip. Use units 'metric' (centimetres) or 'imperial' (inches). Optionally give weight (kg for metric, pounds for imperial) to also get fat mass and lean mass in kilograms. Source: https://hopi.co.uk/body-fat-calculator/
hopi_caesar_cipher
Encode or decode text with a Caesar shift cipher. Each letter is moved along the alphabet by the shift amount; a shift of 13 is ROT13. Only A to Z letters are changed, everything else is left as is. Decoding applies the opposite shift. Source: https://hopi.co.uk/caesar-cipher/
hopi_cagr_calculator
Work out the compound annual growth rate (CAGR) that takes a starting value to an ending value over a number of years. Returns the annual rate, the total growth and the growth multiple. Source: https://hopi.co.uk/cagr-calculator/
hopi_calories_to_kj
Convert food energy between kilocalories (kcal) and kilojoules (kJ) using the exact factor 1 kcal = 4.184 kJ. Give an amount and its unit ('kcal' or 'kj'); returns both values. Source: https://hopi.co.uk/calories-to-kj/
hopi_case_converter
Convert text to a different letter case. 'upper' is UPPERCASE, 'lower' is lowercase, 'title' capitalises the first letter of each word, and 'sentence' capitalises the first letter of each sentence. Source: https://hopi.co.uk/case-converter/
hopi_cat_age_calculator
Convert a cat's age in years to an approximate human age, using the standard 15, 24, then 4 a year chart. Returns the human-equivalent age and the cat's life stage. Source: https://hopi.co.uk/cat-age-calculator/
hopi_celsius_to_fahrenheit
Convert a temperature between Celsius and Fahrenheit. Also returns Kelvin. Set direction to 'c-to-f' or 'f-to-c'. Source: https://hopi.co.uk/celsius-to-fahrenheit/
hopi_character_counter
Count the characters in a block of text, including a count with spaces removed, the word count, how many SMS messages it would take to send, and the Twitter/X characters remaining out of 280. Source: https://hopi.co.uk/character-counter/
hopi_cipher_identifier
Identify what encoding or classical cipher a piece of text probably is (Base64, Base32, hex, binary, octal or decimal ASCII, URL encoding, HTML entities, Morse, Caesar or ROT-N, Atbash, reversed text) or recognise it as a UUID, IPv4 address, Unix timestamp, JWT or hash digest. Returns ranked candidates with confidence and a decoded preview, then auto-decodes nested layers (up to 8) while a step is at least 60% confident. Cannot break keyed encryption such as AES. Source: https://hopi.co.uk/cipher-identifier/
hopi_cm_to_feet
Convert a height between centimetres and feet/inches. Direction 'cm-to-feet' takes cm and returns feet and inches. Direction 'feet-to-cm' takes feet and inches and returns cm. Source: https://hopi.co.uk/cm-to-feet/
hopi_cmyk_to_rgb
Convert print CMYK values (each 0 to 100) to on-screen RGB and hex, or convert RGB (each 0 to 255) the other way to CMYK. Uses the standard device-independent conversion. Source: https://hopi.co.uk/cmyk-to-rgb/
hopi_coin_flip
Flip a fair coin one or more times. Returns each result plus a tally of heads and tails. Source: https://hopi.co.uk/coin-flip/
hopi_colour_name_finder
Find the named CSS colour that exactly or most closely matches a hex code, using straight-line distance in RGB space across the 148 named CSS colours. Source: https://hopi.co.uk/colour-name-finder/
hopi_colour_palette_generator
Generate a five-swatch colour palette from a base hex colour using a chosen scheme: analogous, complementary, triadic or mixed. Supporting swatches carry a small random variation, so results vary slightly each call. Source: https://hopi.co.uk/colour-palette-generator/
hopi_colour_picker
Given a six-digit hex colour code (with or without a leading #), return its hex, RGB and HSL values. Source: https://hopi.co.uk/colour-picker/
hopi_colour_shades_generator
From a base hex colour, generate five progressively lighter tints (mixed towards white) and five progressively darker shades (mixed towards black), each in five equal steps of one sixth. Source: https://hopi.co.uk/colour-shades-generator/
hopi_combination_generator
List every way to choose r items from a list, ignoring order (combinations). Returns the total count and the combinations themselves (the first 5000). Source: https://hopi.co.uk/combination-generator/
hopi_compound_interest_calculator
Project savings growth from a starting deposit plus a regular monthly contribution, compounded monthly with contributions added at the end of each month. Returns the final balance, total paid in and interest earned. Amounts in GBP, rate is the annual rate as a percentage. Source: https://hopi.co.uk/compound-interest-calculator/
hopi_contrast_checker
Work out the WCAG contrast ratio between a foreground (text) colour and a background colour, both as hex codes, and report whether it passes AA and AAA for normal and large text. Source: https://hopi.co.uk/contrast-checker/
hopi_cron_expression_parser
Translate a standard five-field cron expression (minute, hour, day-of-month, month, day-of-week) into plain English. Understands stars, steps, ranges, lists and month and day names, plus shortcuts like @daily and @hourly. Source: https://hopi.co.uk/cron-expression-parser/
hopi_crypto_profit_calculator
Work out profit or loss on a crypto trade from buy price, quantity and an optional per-side fee percentage. Returns breakeven price always, and profit, return percentage and total fees once a sell price is given. All figures are treated as GBP. Source: https://hopi.co.uk/crypto-profit-calculator/
hopi_css_gradient_generator
Build a ready-to-use CSS gradient from two colours. Choose a linear gradient with an angle in degrees, or a radial gradient. Returns the gradient value and a full background declaration. Source: https://hopi.co.uk/css-gradient-generator/
hopi_css_minifier
Minify CSS by removing comments and needless whitespace, while preserving quoted strings and the spaces inside calc() expressions. Returns the minified CSS with before and after byte sizes. Source: https://hopi.co.uk/css-minifier/
hopi_csv_to_json
Convert CSV text into a JSON array, following standard CSV quoting rules for embedded commas, quotes and line breaks. With headers on, the first row becomes object keys; with headers off, each row is an array of strings. Source: https://hopi.co.uk/csv-to-json/
hopi_cups_to_grams
Convert US cups of a common baking ingredient to grams (approximate). Ingredients: flour (plain flour), caster (caster sugar), brown (packed brown sugar), butter, cocoa (cocoa powder), oats, rice (uncooked rice), icing (icing sugar). Source: https://hopi.co.uk/cups-to-grams/
hopi_currency_converter
Convert an amount of money from one currency to another using Hopi's live mid-market exchange rates (updated hourly, 150+ currencies). Use ISO 4217 codes such as GBP, EUR, USD, JPY. Source: https://hopi.co.uk/currency-converter/
hopi_data_size_converter
Convert a digital storage size between units. Units: B (bytes), KB, MB, GB, TB. By default 1 KB = 1000 bytes (decimal, as storage is sold). Set binary to true for 1 KB = 1024 bytes (as Windows reports drive sizes). Source: https://hopi.co.uk/data-size-converter/
hopi_date_calculator
Add or subtract a number of days, weeks, months or years from a date. Dates use the YYYY-MM-DD format. Months and years are clamped to the last day of the target month where needed. Returns the resulting date. Source: https://hopi.co.uk/date-calculator/
hopi_day_of_week_calculator
Find which day of the week a given date falls on. Dates use the YYYY-MM-DD format. Also reports which weekday that same day and month falls on in the current year. Source: https://hopi.co.uk/day-of-week-calculator/
hopi_day_rate_calculator
Convert between a contractor day rate and an annual salary equivalent using a chosen number of billable working days per year (default 220). Mode 'to_salary' turns a day rate into yearly, monthly and weekly figures; mode 'to_rate' turns a salary into a day rate. Gross amounts in GBP, before tax. Source: https://hopi.co.uk/day-rate-calculator/
hopi_days_between_dates
Count the number of days between two dates, with the total also shown in weeks and in weekdays (Monday to Friday). Dates use the YYYY-MM-DD format. Set inclusive to true to count both end days. Source: https://hopi.co.uk/days-between-dates/
hopi_days_until_christmas
Count the number of sleeps until the next Christmas Day (25 December). Uses today's date by default, or an optional 'from' date in YYYY-MM-DD format. Source: https://hopi.co.uk/days-until-christmas/
hopi_dca_calculator
Work out the average cost basis across a series of pound-cost-averaged buys. Each buy is an amount of money spent and the price paid per unit. Returns total invested, coins acquired and average cost, plus current value and unrealised profit or loss if a current price is given. Figures are treated as GBP. Source: https://hopi.co.uk/dca-calculator/
hopi_dice_roller
Roll one or more dice with a given number of sides. Returns each die result plus the total, highest and lowest. Source: https://hopi.co.uk/dice-roller/
hopi_diff_checker
Compare two texts line by line using a longest common subsequence diff, and report which lines were added and which were removed. An edited line shows as one removed line plus one added line. Comparison is exact, including spaces and case. Source: https://hopi.co.uk/diff-checker/
hopi_discount_calculator
Work out a discount and sale price. Mode 'pct': a percentage off a price. Mode 'fixed': a fixed pound amount off a price. Mode 'find': the discount percentage from an original price and a final price. All money figures are in pounds. Source: https://hopi.co.uk/discount-calculator/
hopi_dog_age_calculator
Convert a dog's age in years to an approximate human age, using the standard veterinary chart. The later rate depends on the dog's size: small, medium or large. Returns the human-equivalent age. Source: https://hopi.co.uk/dog-age-calculator/
hopi_download_time_calculator
Estimate how long a download takes. Give a file size with its unit (MB, GB, TB) and a connection speed with its unit (Mbps or Gbps in bits per second, or MBps in bytes per second). Returns a human-readable duration and the time in seconds. Source: https://hopi.co.uk/download-time-calculator/
hopi_due_date_calculator
Estimate a pregnancy due date from the first day of the last menstrual period (LMP) and cycle length. Method: adjust the LMP by (cycle - 28) days, then add 280 days for the due date. Also returns the dates the second and third trimesters begin (LMP-adjusted + 84 and + 182 days). Dates are ISO 'YYYY-MM-DD'. Source: https://hopi.co.uk/due-date-calculator/
hopi_dummy_data_generator
Generate fake but safe UK test records. Phone numbers come from Ofcom's reserved drama ranges and emails use RFC 2606 example domains, so no record can reach a real person. Returns an array of records, plus CSV text. Source: https://hopi.co.uk/dummy-data-generator/
hopi_email_link_generator
Build a correctly percent-encoded mailto link from to, cc, bcc, subject and body fields, plus a ready to paste HTML anchor snippet. Spaces are encoded as %20 and line breaks as %0D%0A, as the mailto standard expects. Source: https://hopi.co.uk/email-link-generator/
hopi_emoji_remover
Remove emoji from a block of text, leaving the words and normal punctuation intact. Joined emoji sequences (such as a family or a flag) count as a single emoji. The copyright, registered and trademark symbols are kept. Returns the cleaned text and how many emoji were removed. Source: https://hopi.co.uk/emoji-remover/
hopi_energy_cost_calculator
Work out the running cost of an electrical appliance from its power in watts, hours used per day and your electricity unit price in pence per kWh. Returns daily, weekly, monthly and yearly cost plus kWh used. Costs in GBP. Source: https://hopi.co.uk/energy-cost-calculator/
hopi_env_to_json
Convert between a .env file and a JSON object. In env-to-json mode, each line is split on its first equals sign into a key and value, blank and commented lines are skipped, a leading export is removed, and matching surrounding quotes are stripped (double-quoted values also unescape \n); duplicate keys keep the last value. In json-to-env mode, a JSON object becomes KEY=value lines, quoting values that contain spaces, a hash or a newline. Source: https://hopi.co.uk/env-to-json/
hopi_eth_address_checksum
Validate an Ethereum address's EIP-55 capitalisation checksum and return the correctly checksummed form. Reports whether the input is already checksummed, lacks a checksum (all one case), or fails the checksum. Uses keccak-256 exactly as EIP-55 specifies. Source: https://hopi.co.uk/eth-address-checksum/
hopi_eth_unit_converter
Convert an amount given in wei, gwei or ETH into all three units, using exact 18-decimal integer maths (no floating point error). 1 ETH is 1e18 wei; 1 gwei is 1e9 wei. Source: https://hopi.co.uk/eth-unit-converter/
hopi_euromillions_generator
Generate random EuroMillions lines. Each line has 5 main numbers from 1 to 50 and 2 Lucky Stars from 1 to 12. Source: https://hopi.co.uk/euromillions-generator/
hopi_event_wine_calculator
Work out how many bottles of red, white and Champagne to buy for an event, from the number of guests and glasses per guest. Ticking different wines splits a colour into one wine per glass, each poured once for every guest. Source: https://hopi.co.uk/event-wine-calculator/
hopi_fortune_cookie
Crack open a virtual fortune cookie and receive a random cheerful fortune. Returns the fortune. Source: https://hopi.co.uk/fortune-cookie/
hopi_fraction_calculator
Add, subtract, multiply or divide two fractions, giving the simplified result, a mixed number where relevant, and the decimal value. Each fraction is a numerator over a denominator, all whole numbers (numerators may be negative). Source: https://hopi.co.uk/fraction-calculator/
hopi_fraction_to_decimal
Convert between fractions and decimals. Mode 'toDecimal': give a numerator and denominator (whole numbers) to get the decimal and percentage. Mode 'toFraction': give a decimal to get the closest simplified fraction (denominator up to 10,000), noting whether it is exact. Source: https://hopi.co.uk/fraction-to-decimal/
hopi_fuel_cost_calculator
Estimate the fuel cost of a journey from the distance in miles, the car's fuel economy in miles per gallon (UK gallon) and the pump price in pence per litre. Optionally double it for a return trip and split between passengers. Returns total cost, litres used and cost per person. Costs in GBP. Source: https://hopi.co.uk/fuel-cost-calculator/
hopi_hash_generator
Compute the SHA-256, SHA-1 or SHA-512 hash of a piece of text and return the hex digest. Uses WebCrypto on Hopi's server. SHA-1 is included for compatibility with older systems only and should not be used for anything new. Source: https://hopi.co.uk/hash-generator/
hopi_hash_identifier
Identify the most likely algorithms behind a hash string from its length, character set and any prefix. Covers MD5, NTLM, MD4, SHA-1, RIPEMD-160, SHA-224/256/384/512, the SHA3 family, CRC32, bcrypt, Argon2, sha512crypt, sha256crypt and md5crypt, plus Base64 length hints. A hash does not carry its algorithm, so results are ranked best guesses, not proof. Source: https://hopi.co.uk/hash-identifier/
hopi_heart_rate_zones
Estimate maximum heart rate and five training zones (bpm) from age. Max HR = 220 - age. Method 'max' uses percentages of max HR (50-60, 60-70, 70-80, 80-90, 90-100%). Method 'karvonen' uses heart rate reserve and needs restingHeartRate: zone = (maxHR - resting) x intensity + resting. Source: https://hopi.co.uk/heart-rate-zones/
hopi_hex_to_rgb
Convert a hex colour code (3, 6 or 8 digits, with or without a leading #) to its RGB and HSL values. Source: https://hopi.co.uk/hex-to-rgb/
hopi_holiday_entitlement_calculator
Work out UK statutory paid holiday entitlement from the number of days worked per week, using 5.6 weeks a year capped at the statutory 28 days. Optionally scale to a part-year by the number of months worked. Returns entitlement in days and weeks. Source: https://hopi.co.uk/holiday-entitlement-calculator/
hopi_hourly_to_salary
Convert between an hourly pay rate and an annual salary based on hours worked per week (52 weeks a year). Mode 'to_salary' turns an hourly rate into annual, monthly and weekly pay; mode 'to_hourly' turns a salary into an hourly rate. Gross amounts in GBP, before tax. Source: https://hopi.co.uk/hourly-to-salary/
hopi_hours_calculator
Work out the hours worked between a start time and an end time, minus an optional unpaid break. Times use 24-hour HH:MM format. Handles overnight shifts where the end time is earlier than the start. Returns the worked time as hours and minutes and as decimal hours. Source: https://hopi.co.uk/hours-calculator/
hopi_hsl_converter
Convert a hex colour code to hue, saturation and lightness (HSL), or convert HSL values to hex and RGB. Source: https://hopi.co.uk/hsl-converter/
hopi_html_escape
Escape the five special HTML characters (& < > " ') into entities so text is safe to place in HTML, or unescape named and numeric HTML entities back into plain characters. Source: https://hopi.co.uk/html-escape/
hopi_http_status_codes
Look up a standard HTTP status code by number and get its name, meaning and class (1xx to 5xx), or search all standard codes by a word in the number, name or description. Source: https://hopi.co.uk/http-status-codes/
hopi_iban_validator
Validate an IBAN or generate a test IBAN. Pass 'iban' to check it: the tool normalises it (uppercase, no spaces), confirms the length matches the country's published length, and runs the mod-97 checksum (move the first four characters to the end, map letters to numbers A=10 to Z=35, valid when the number mod 97 is 1). Pass 'country' (a two-letter ISO code) to generate a structurally valid TEST IBAN with a random bank and account portion and correct check digits. Generated IBANs are test values only and are not tied to any real account. All processing is local; nothing is stored. Source: https://hopi.co.uk/iban-validator/
hopi_ics_generator
Build a .ics (iCalendar, RFC 5545) calendar file for a single event and return the file text. Give a title, startDate and endDate as 'YYYY-MM-DD'. For timed events give startTime and endTime as 'HH:MM' (24-hour, read in the caller's local time zone and stored as UTC); set allDay true for an all-day event instead. Location and description are optional. Returns the .ics text ready to save. Source: https://hopi.co.uk/ics-generator/
hopi_inflation_calculator
Adjust a money amount for UK inflation. Mode 'cpi' uses the ONS monthly CPI index (2015 = 100) between two months from January 1988 to August 2026 and returns the adjusted value, total change and average annual rate. Mode 'custom' compounds a chosen annual rate over a number of years. Amounts in GBP. Source: https://hopi.co.uk/inflation-calculator/
hopi_json_formatter
Pretty print, minify or validate JSON. Formatting and minifying only change whitespace; key order, values and structure stay exactly as they were. Returns the output text or a clear parse error. Source: https://hopi.co.uk/json-formatter/
hopi_json_to_csv
Convert a JSON array of objects into CSV. The union of all keys becomes the header row in first-seen order, missing keys become empty cells, and nested objects or arrays are written back as compact JSON in the cell. Output follows RFC 4180 quoting. Source: https://hopi.co.uk/json-to-csv/
hopi_json_to_typescript
Convert a JSON sample into TypeScript interfaces and types. Objects become named interfaces (PascalCase from their key), nested objects get their own interfaces, arrays become element-type arrays with keys merged across all elements (keys missing from some elements are marked optional), and null values are folded into unions such as string | null. Empty arrays become unknown[] and empty objects become Record<string, unknown>. Runs on Hopi's server; nothing is stored. Source: https://hopi.co.uk/json-to-typescript/
hopi_json_yaml_converter
Convert data between JSON and YAML in both directions. JSON to YAML parses with JSON.parse and serialises with js-yaml at two-space indent; YAML to JSON parses with js-yaml and prints with JSON.stringify. Runs on Hopi's server; nothing is stored. Source: https://hopi.co.uk/json-yaml-converter/
hopi_jwt_decoder
Decode a JSON Web Token's header and payload from base64url. The signature is never verified, so a decoded claim proves nothing on its own. Reports the algorithm, the exp, iat and nbf time claims, and whether the token is expired. A leading Bearer prefix and whitespace are handled. Source: https://hopi.co.uk/jwt-decoder/
hopi_kg_to_stone
Convert a weight in kilograms to UK stone and pounds. Returns whole stone plus remaining pounds, and the totals in pounds and decimal stone. Source: https://hopi.co.uk/kg-to-stone/
hopi_leap_year_checker
Check whether a year is a leap year, applying the divisible-by-4, century, and divisible-by-400 rules. Returns the verdict, the divisibility tests, and the next and previous leap years. Source: https://hopi.co.uk/leap-year-checker/
hopi_length_converter
Convert a length from one unit to another. Units: mm, cm, m, km, in (inches), ft (feet), yd (yards), mi (miles). Source: https://hopi.co.uk/length-converter/
hopi_litres_to_pints
Convert between litres and pints. Direction 'litres-to-pints' takes litres and returns UK pints, US pints and millilitres. Direction 'pints-to-litres' takes UK pints and returns litres. Source: https://hopi.co.uk/litres-to-pints/
hopi_loan_calculator
Work out the monthly repayment on a loan from the amount borrowed, the annual interest rate and the term in years, using the standard amortising formula. Returns the monthly payment, total repaid and total interest. Amounts in GBP. Source: https://hopi.co.uk/loan-calculator/
hopi_lorem_ipsum_generator
Generate lorem ipsum placeholder text. Choose whether the count is a number of paragraphs, sentences or words, and how many. Limits are 100 paragraphs, 500 sentences or 2000 words. Source: https://hopi.co.uk/lorem-ipsum-generator/
hopi_lottery_number_generator
Generate random lines for a UK lottery game: Lotto (6 numbers from 1 to 59), Thunderball (5 from 1 to 39 plus a Thunderball from 1 to 14) or Set For Life (5 from 1 to 47 plus a Life Ball from 1 to 10). Source: https://hopi.co.uk/lottery-number-generator/
hopi_magic_8_ball
Ask the Magic 8 Ball a yes or no question and receive one of its twenty classic answers at random. Returns the answer. Source: https://hopi.co.uk/magic-8-ball/
hopi_margin_calculator
Work out profit, gross margin and markup from a cost price and a selling price. Margin is profit as a percentage of the selling price; markup is profit as a percentage of the cost. Amounts in GBP. Source: https://hopi.co.uk/margin-calculator/
hopi_markdown_previewer
Render a small, safe subset of markdown to HTML: headings (# to ###), bold, italic, links (http, https or mailto only), inline code, fenced code blocks, bulleted and numbered lists, and blockquotes. Every character is HTML-escaped first, so raw HTML is shown as text and never executed. Source: https://hopi.co.uk/markdown-previewer/
hopi_market_cap_calculator
Calculate a coin's market cap (price times circulating supply) and fully diluted valuation, or work backwards to the price implied by a target market cap. Works in any currency; nothing is looked up. Source: https://hopi.co.uk/market-cap-calculator/
hopi_meta_tag_generator
Build a complete HTML head snippet from page details: title, meta description, canonical link, Open Graph and Twitter card tags. Returns the ready-to-paste snippet plus character counts. Source: https://hopi.co.uk/meta-tag-generator/
hopi_miles_to_km
Convert between miles and kilometres. Direction 'miles-to-km' takes miles and returns kilometres. Direction 'km-to-miles' takes kilometres and returns miles. Source: https://hopi.co.uk/miles-to-km/
hopi_military_time_converter
Convert between 24-hour (military) time and 12-hour clock time. Direction '24h-to-12h' takes a 24-hour time like '1430' or '14:30'. Direction '12h-to-24h' takes a 12-hour time like '2:30' with a meridiem of am or pm (the meridiem can also be written in the time string). Source: https://hopi.co.uk/military-time-converter/
hopi_minutes_to_hours
Convert a number of minutes into hours and minutes, or convert hours (plus optional extra minutes) into total minutes. Set mode to 'minutesToHours' or 'hoursToMinutes'. Returns a clock-style breakdown and decimal hours. Source: https://hopi.co.uk/minutes-to-hours/
hopi_moon_phase_calculator
Work out the moon phase for a date, based on the synodic month since a known new moon. Dates use the YYYY-MM-DD format and default to today. Returns the phase name, illuminated percentage, moon age in days, and the next full and new moons. Source: https://hopi.co.uk/moon-phase-calculator/
hopi_morse_code_translator
Translate text into international Morse code, or Morse code back into text. Letters are separated by spaces and words by a forward slash. When decoding, underscores are treated as dashes and pipes as word separators. Unknown Morse sequences appear as # in the output. Source: https://hopi.co.uk/morse-code-translator/
hopi_mortgage_calculator
Work out the monthly payment on a repayment mortgage at a constant interest rate, using the standard amortising formula. Returns the monthly payment, total repaid and total interest. Fees and rate changes are not included. Amounts in GBP. Source: https://hopi.co.uk/mortgage-calculator/
hopi_mortgage_overpayment_calculator
See how much time and interest a regular monthly overpayment saves on a repayment mortgage. Give the current balance, annual rate, remaining term in years and the extra amount paid each month. Returns the time saved, interest saved, new payoff time and the monthly payment. Amounts in GBP. Source: https://hopi.co.uk/mortgage-overpayment-calculator/
hopi_mpg_converter
Convert fuel economy between UK miles per gallon and litres per 100 km. Direction 'mpg-to-l100' takes UK mpg. Direction 'l100-to-mpg' takes litres per 100 km. Also returns US mpg, km per litre and miles per litre. Source: https://hopi.co.uk/mpg-converter/
hopi_national_insurance_calculator
Work out UK employee Class 1 National Insurance for the 2026/27 tax year from an annual gross salary. Uses the primary threshold of £12,570, upper earnings limit of £50,270, 8% between them and 2% above. Returns NI due per year, month and week plus the effective rate. Amounts in GBP. Source: https://hopi.co.uk/national-insurance-calculator/
hopi_nato_phonetic_alphabet
Spell text out using the NATO phonetic alphabet (Alfa, Bravo, Charlie and so on), or convert a phonetic spelling back into plain text. Spaces become (space). When converting back, common variants such as Alpha, Juliet, Xray, Niner and Fife are accepted; unrecognised words appear as #. Source: https://hopi.co.uk/nato-phonetic-alphabet/
hopi_net_to_gross
Work out the gross salary needed to achieve a desired take-home (net) pay for the 2026/27 tax year in England, Wales and Northern Ireland, using code 1257L income tax bands with personal allowance taper and employee National Insurance. Give the net figure as yearly or monthly. Returns the required gross, tax and NI. Amounts in GBP. Source: https://hopi.co.uk/net-to-gross/
hopi_number_base_converter
Convert a whole number from one base to another between binary, octal, decimal and hexadecimal. Uses BigInt so values of any size convert exactly. Returns the value in the requested base plus all four bases. Source: https://hopi.co.uk/number-base-converter/
hopi_number_to_words
Convert a number into written English words. Set currency to true to write it as UK pounds and pence (cheque style, ending 'only'). Supports up to 999,999,999,999 with decimals to two places. Source: https://hopi.co.uk/number-to-words/
hopi_oven_temperature_converter
Convert an oven temperature. Scale 'c' is conventional Celsius, 'fan' is fan/convection Celsius, 'f' is Fahrenheit, 'gas' is UK gas mark (1 to 9). Returns conventional Celsius, fan Celsius, Fahrenheit and the nearest gas mark. Source: https://hopi.co.uk/oven-temperature-converter/
hopi_overtime_pay_calculator
Work out gross overtime pay from a base hourly rate and hours worked at three multipliers: standard (1x), time and a half (1.5x) and double time (2x). At least one hours figure is required. Returns pay at each rate, the total and total hours. Gross pay in GBP, before tax and NI. Source: https://hopi.co.uk/overtime-pay-calculator/
hopi_password_strength_checker
Estimate how strong a password is: an entropy estimate in bits, a rough offline crack time (assuming ten billion guesses a second), a 0 to 4 score with a verdict, and warnings about weak patterns such as dictionary words, sequences and repeats. Source: https://hopi.co.uk/password-strength-checker/
hopi_percentage_calculator
Work out percentages three ways. Mode 'of': what is P percent of a number. Mode 'what': what percentage the part is of the whole. Mode 'change': the percentage change from a starting value to an end value. Source: https://hopi.co.uk/percentage-calculator/
hopi_percentage_change_calculator
Work out the percentage change from a starting value to an end value, using the starting value as the base. A positive result is an increase, a negative result is a decrease. Source: https://hopi.co.uk/percentage-change-calculator/
hopi_percentage_decrease_calculator
Decrease a number by a percentage and see the new value and the amount taken off. For example, 250 decreased by 15 percent. Source: https://hopi.co.uk/percentage-decrease-calculator/
hopi_percentage_difference_calculator
Work out the percentage difference between two values using the average-based formula: the absolute gap divided by the average of the two, times 100. The result is symmetric, so the order of the two values does not matter. Source: https://hopi.co.uk/percentage-difference-calculator/
hopi_percentage_increase_calculator
Increase a number by a percentage and see the new value and the amount added. For example, 250 increased by 15 percent. Source: https://hopi.co.uk/percentage-increase-calculator/
hopi_position_size_calculator
Work out how large a position to take so that hitting the stop-loss loses only a chosen percentage of the account. Enter account size, risk percentage, entry price and stop-loss price. Returns units to buy, position value, amount at risk and stop distance. Figures are treated as GBP. Source: https://hopi.co.uk/position-size-calculator/
hopi_power_converter
Convert power from one unit to another. Units: w (watts), kw (kilowatts), hp (mechanical horsepower), ps (metric horsepower, PS). Source: https://hopi.co.uk/power-converter/
hopi_pressure_converter
Convert pressure from one unit to another. Units: bar, psi (pounds per square inch), kpa (kilopascals), atm (atmospheres). Source: https://hopi.co.uk/pressure-converter/
hopi_prime_factorisation_calculator
Check whether a whole number (2 to 1,000,000,000,000,000) is prime, break it into its prime factors in power form, count its divisors, and list them. Uses trial division. Source: https://hopi.co.uk/prime-factorisation-calculator/
hopi_pro_rata_salary_calculator
Work out a pro rata salary for part-time hours by scaling a full-time salary by the ratio of your hours to full-time hours. Returns the pro rata yearly, monthly and weekly pay and the fraction of full-time. Amounts in GBP, gross before tax. Source: https://hopi.co.uk/pro-rata-salary-calculator/
hopi_product_feed_generator
Turn product rows into a platform-valid product feed: Meta (Facebook and Instagram) RSS 2.0, Google Merchant RSS 2.0, Atom 1.0 or generic RSS 2.0, using the g: namespace where the platform expects it. Each row is validated (required fields, price as 12.99 GBP, availability and condition values, http links, unique ids); rows that fail are skipped and listed. Returns the XML, counts and errors. Source: https://hopi.co.uk/product-feed-generator/
hopi_random_colour_generator
Generate a random colour and return its hex, RGB and HSL values. Each of the red, green and blue channels gets an independent value from 0 to 255. Source: https://hopi.co.uk/random-colour-generator/
hopi_random_coordinates
Generate random geographic coordinates that are uniform by surface area across the globe (points are not bunched at the poles). Returns latitude and longitude in decimal degrees. Source: https://hopi.co.uk/random-coordinates/
hopi_random_letter_generator
Generate random letters from the alphabet, optionally limited to vowels or consonants. Returns the letters as a list. Source: https://hopi.co.uk/random-letter-generator/
hopi_random_number_generator
Generate one or more random whole numbers within a range (inclusive), optionally with no repeats. Returns the numbers as a list. Source: https://hopi.co.uk/random-number-generator/
hopi_random_team_generator
Shuffle a list of names and deal them evenly into a set number of teams. Returns each team's members. Source: https://hopi.co.uk/random-team-generator/
hopi_random_word_generator
Generate random everyday English nouns, with no repeats. Returns the words as a list. Source: https://hopi.co.uk/random-word-generator/
hopi_ratio_calculator
Work with ratios. Mode 'simplify': reduce a ratio a : b to its lowest terms, and give the 1 : n form and the decimal a / b. Mode 'solve': find the missing value x in the equivalent ratio a : b = c : x using cross multiplication. All inputs must be positive. Source: https://hopi.co.uk/ratio-calculator/
hopi_reading_time_calculator
Estimate how long a block of text takes to read. Returns a silent reading time (225 words per minute) and a read-aloud time (130 words per minute), along with the word count. Source: https://hopi.co.uk/reading-time-calculator/
hopi_redundancy_pay_calculator
Work out UK statutory redundancy pay for redundancies on or after 6 April 2026, using the gov.uk count-back method: for each full year of service (up to 20), 1.5 weeks if worked aged 41+, 1 week aged 22 to 40, and 0.5 weeks under 22. Weekly pay is capped at £751 and the total at £22,530. At least 2 full years of service are needed. Amounts in GBP. Source: https://hopi.co.uk/redundancy-pay-calculator/
hopi_remove_duplicate_lines
Remove duplicate lines from a block of text, keeping the first occurrence of each line in its original order. Can optionally ignore letter case when deciding what counts as a duplicate. Returns the deduplicated text plus how many lines were kept and removed. Source: https://hopi.co.uk/remove-duplicate-lines/
hopi_remove_extra_spaces
Tidy up spacing in text: collapse runs of spaces, tabs and non-breaking spaces down to a single space and trim each line. Can optionally also remove blank lines. Line breaks between lines are kept. Source: https://hopi.co.uk/remove-extra-spaces/
hopi_remove_line_breaks
Remove line breaks from text. In 'spaces' mode every line is joined into one with single spaces. In 'paragraphs' mode blank lines are treated as paragraph breaks, so text is joined within each paragraph while the blank line between paragraphs is preserved. Source: https://hopi.co.uk/remove-line-breaks/
hopi_reverse_text
Reverse text in one of three ways. 'characters' reverses the entire text character by character. 'words' reverses the order of words on each line. 'each' keeps the word order but reverses the letters within each word. Source: https://hopi.co.uk/reverse-text/
hopi_rgb_to_hex
Convert red, green and blue values (each a whole number from 0 to 255) to an uppercase hex colour code. Source: https://hopi.co.uk/rgb-to-hex/
hopi_ring_size_converter
Convert a ring size between UK, US and millimetre scales. Mode 'uk' takes a UK letter F to Z (add 1/2 for half sizes, e.g. 'N' or 'N 1/2'). Mode 'us' takes a US number 2.75 to 12.75. Mode 'mm' takes an inside circumference in mm (about 44 to 69). Returns UK size, US size, circumference and inside diameter. Source: https://hopi.co.uk/ring-size-converter/
hopi_robots_txt_generator
Build a robots.txt file from allow and disallow rules grouped by user agent, with an optional sitemap line. You can pass a preset ('allow' all, 'block' all, 'wordpress') or your own rules array. Source: https://hopi.co.uk/robots-txt-generator/
hopi_roman_numerals_converter
Convert between numbers and Roman numerals, both directions, for whole numbers from 1 to 3999. Give a number (e.g. 2026) to get its numeral, or a Roman numeral (e.g. MMXXVI) to get the number. The direction is detected automatically from the input. Source: https://hopi.co.uk/roman-numerals-converter/
hopi_rounding_calculator
Round a number to a chosen number of decimal places or significant figures, with halves always rounded up (away from zero). Mode 'dp': decimal places, 0 to 12. Mode 'sf': significant figures, 1 to 15. Source: https://hopi.co.uk/rounding-calculator/
hopi_running_pace_calculator
Work out running pace, finish time or distance, in kilometres or miles. Mode 'pace' needs distance and timeSeconds; mode 'time' needs distance and paceSeconds (seconds per unit); mode 'distance' needs timeSeconds and paceSeconds. Distance is in the chosen unit. Returns pace per km and per mile, speed in km/h and mph, distance and total time. Source: https://hopi.co.uk/running-pace-calculator/
hopi_satoshi_converter
Convert satoshis to BTC, mBTC and bits, or convert BTC to satoshis, mBTC and bits. Uses exact whole-satoshi integer maths. 1 BTC is 100,000,000 satoshis. Source: https://hopi.co.uk/satoshi-converter/
hopi_savings_goal_calculator
Plan a savings goal, compounded monthly. Mode 'time' works out how long a monthly deposit takes to reach a target. Mode 'monthly' works out the monthly saving needed to reach a target within a number of years. Both take an optional starting balance and an annual interest rate. Amounts in GBP. Source: https://hopi.co.uk/savings-goal-calculator/
hopi_schema_markup_generator
Build valid JSON-LD structured data using schema.org. Supports FAQ pages, articles, local businesses and breadcrumb lists. Returns the JSON-LD object and a ready-to-paste script snippet. Source: https://hopi.co.uk/schema-markup-generator/
hopi_scientific_calculator
Evaluate a maths expression following the standard order of operations (BODMAS). Supports + - * / ^ (power), ! (factorial), % (as divide by 100), brackets, the constants pi and e, and the functions sin, cos, tan, asin, acos, atan, ln, log (base 10) and sqrt. Set angleMode to 'deg' (default) or 'rad' for trigonometry. Source: https://hopi.co.uk/scientific-calculator/
hopi_secret_santa_generator
Draw Secret Santa gift pairings from a list of names. Every person gives to exactly one other person, and nobody is assigned to themselves (a derangement). Returns the giver to receiver pairs. Source: https://hopi.co.uk/secret-santa-generator/
hopi_shoe_size_converter
Convert a UK shoe size to approximate EU and US sizes. Set sex to 'men' (UK 5 to 13) or 'women' (UK 2 to 9). UK size must be in whole or half steps. Source: https://hopi.co.uk/shoe-size-converter/
hopi_sleep_calculator
Suggest sleep times using 90-minute cycles plus 15 minutes to fall asleep. Mode 'wake' takes a wake time and returns the best bedtimes (wake - 15 - cycles x 90 minutes). Mode 'bedtime' takes a bedtime and returns the best wake times (bedtime + 15 + cycles x 90 minutes). Both return options for 6, 5, 4 and 3 cycles. Times are 'HH:MM' 24-hour. Source: https://hopi.co.uk/sleep-calculator/
hopi_slot_machine_picker
Spin a slot machine reel of names or options and pick one at random. Every item has an equal chance. Returns the chosen item. Source: https://hopi.co.uk/slot-machine-picker/
hopi_slug_generator
Turn any title or text into a clean URL slug: lowercase, accents stripped, and every run of spaces, punctuation and symbols collapsed to a single hyphen, with hyphens trimmed from the ends. Source: https://hopi.co.uk/slug-generator/
hopi_small_text_generator
Convert text into decorative Unicode styles. 'superscript' uses tiny raised characters, 'smallcaps' uses small capital letters, and 'fullwidth' uses wide monospaced characters. Any character with no styled equivalent is left unchanged. Source: https://hopi.co.uk/small-text-generator/
hopi_special_characters
List special characters and symbols grouped by category: arrows, stars and hearts, maths, currency, punctuation, legal marks and accents. Optionally filter to a single group. Returns the characters ready to copy. Source: https://hopi.co.uk/special-characters/
hopi_speed_converter
Convert a speed from one unit to another. Units: mph (miles per hour), kmh (kilometres per hour), ms (metres per second), kn (knots), mach (Mach, at 340.29 m/s). Source: https://hopi.co.uk/speed-converter/
hopi_spin_the_bottle
Spin the bottle and pick one player at random from those in the circle. Every player has an equal chance. Returns the chosen player. Source: https://hopi.co.uk/spin-the-bottle/
hopi_sql_formatter
Format a SQL query: uppercase the keywords, put each clause on its own line and indent conditions, while leaving quoted strings, identifiers, numbers and comments untouched. Only whitespace and keyword case change. Source: https://hopi.co.uk/sql-formatter/
hopi_staking_calculator
Turn a quoted staking rate into a final balance and rewards earned. For an APR rate, choose daily or monthly compounding; for an APY rate, compounding is already included. Returns the final balance, rewards earned and the effective APY. Figures are treated as GBP. Source: https://hopi.co.uk/staking-calculator/
hopi_stamp_duty_calculator
Work out Stamp Duty Land Tax (SDLT) on a property purchase in England and Northern Ireland. Buyer types: 'ftb' first-time buyer (relief up to £500,000, standard rates above), 'home' moving home (main residence), 'additional' second home or buy-to-let (higher rates, only from £40,000). Returns the tax due and the effective rate. Amounts in GBP. Scotland (LBTT) and Wales (LTT) have their own rates. Source: https://hopi.co.uk/stamp-duty-calculator/
hopi_standard_deviation_calculator
Work out the sample and population standard deviation, sample and population variance, mean and count from a list of numbers. Provide the numbers separated by spaces, commas, semicolons or new lines. Sample figures need at least two values. Source: https://hopi.co.uk/standard-deviation-calculator/
hopi_star_sign_calculator
Find the western zodiac star sign for a date of birth. Dates use the YYYY-MM-DD format (only the month and day matter). Returns the sign, its symbol, date range and element. Source: https://hopi.co.uk/star-sign-calculator/
hopi_student_loan_calculator
Work out UK student loan repayments from an annual salary using 2026/27 thresholds. Plans: 'p1' Plan 1 (9% above £26,900), 'p2' Plan 2 (9% above £29,385), 'p4' Plan 4 (9% above £33,795), 'p5' Plan 5 (9% above £25,000), 'pg' Postgraduate Loan (6% above £21,000). An undergraduate plan can optionally add a Postgraduate Loan on top. Returns yearly and monthly repayments. Amounts in GBP. Source: https://hopi.co.uk/student-loan-calculator/
hopi_take_home_pay_calculator
Work out UK take-home pay from an annual gross salary for the 2026/27 tax year in England, Wales and Northern Ireland, using code 1257L income tax bands (20/40/45%) with personal allowance taper above £100,000, plus employee National Insurance. Returns net pay per year, month and week, and the tax and NI deducted. Amounts in GBP. Source: https://hopi.co.uk/take-home-pay-calculator/
hopi_tarot_reader
Draw a tarot spread from all 78 Rider-Waite-Smith cards, dealt without replacement using cryptographic randomness. Spreads: daily (1 card), past-present-future (3), situation (3: situation, obstacle, advice), decision (5), relationship (6), career (5), celtic (10, Celtic Cross). Returns each position with its card, orientation and keywords, plus counts of Major Arcana and reversed cards. For reflection and fun, not prediction. Source: https://hopi.co.uk/tarot-reader/
hopi_tdee_calculator
Estimate daily calories (TDEE) and BMR using the Mifflin-St Jeor equation. BMR = 10 x kg + 6.25 x cm - 5 x age + (5 for male, -161 for female). TDEE = BMR x activity factor (sedentary 1.2, light 1.375, moderate 1.55, active 1.725, very_active 1.9). Use units 'metric' (heightCm, weightKg) or 'imperial' (heightInches, weightPounds). Also returns mild-loss (-250), loss (-500) and gain (+500) calorie goals. Source: https://hopi.co.uk/tdee-calculator/
hopi_test_card_number_generator
Generate Luhn-valid TEST card numbers for QA and development, or validate a card number. Test numbers pass the Luhn checksum and match a real brand format but are NOT real accounts, are linked to no one, and cannot be charged. Generate mode returns numbers for a brand (Visa, Mastercard, American Express, Discover); validate mode returns whether a number passes Luhn and its detected brand. Runs on Hopi's server; nothing is stored and no bank is contacted. Source: https://hopi.co.uk/test-card-number-generator/
hopi_text_repeater
Repeat a piece of text a chosen number of times, joined by an optional separator, with optional line numbering. Count is capped at 10000 repeats and the output is capped at 100000 characters. Returns the repeated text plus its character and line counts. Source: https://hopi.co.uk/text-repeater/
hopi_text_splitter
Split a long block of text into smaller blocks. In 'length' mode it splits into chunks up to a maximum character size, breaking at spaces where possible, and can add 1/n numbering to each block. In 'delimiter' mode it splits wherever a delimiter appears (use \n for newline, \t for tab). Returns the list of blocks. Source: https://hopi.co.uk/text-splitter/
hopi_time_calculator
Add or subtract two durations, each given as hours and minutes. Returns the total as an H:MM clock value, as decimal hours, and as total minutes. Results can be negative when subtracting. Source: https://hopi.co.uk/time-calculator/
hopi_time_zone_converter
Convert a wall-clock date and time from one time zone to another, using the server's IANA time zone data (so daylight saving is handled). Date uses YYYY-MM-DD and time uses 24-hour HH:MM. Zones are IANA identifiers such as Europe/London or America/New_York. Returns the converted time, the day difference, and both UTC offsets. Source: https://hopi.co.uk/time-zone-converter/
hopi_tip_calculator
Work out a tip on a bill and optionally split the total between people. Returns the tip amount, the total, and the amount per person. Source: https://hopi.co.uk/tip-calculator/
hopi_triangle_calculator
Solve a right-angle triangle from any two given values, at least one of which must be a side. Sides: a (opposite), b (adjacent), c (hypotenuse). angleA is angle A in degrees, between 0 and 90 (the third angle is the 90 degree right angle). Returns all three sides, both non-right angles, the area and the perimeter. Source: https://hopi.co.uk/triangle-calculator/
hopi_ucas_points_calculator
Add up UCAS tariff points from A-level grades using the current tariff: A* 56, A 48, B 40, C 32, D 24, E 16. Give the number of grades at each level. Returns the total points and the number of grades counted. Source: https://hopi.co.uk/ucas-points-calculator/
hopi_unicode_inspector
Inspect text as Unicode. Returns the number of code points (iterated so emoji and other astral characters count as one), the UTF-16 length, the UTF-8 byte count, and per-character details: the character, its code point as U+XXXX, its decimal value, its UTF-8 bytes as hex, its HTML entity and a JavaScript escape. The character list is capped at 2000 entries. Source: https://hopi.co.uk/unicode-inspector/
hopi_unit_price_calculator
Compare the unit price of two or more items to find the best value. Each item has a price in GBP, a quantity and a unit ('g', 'kg', 'ml', 'l' or 'each'). Weights are compared per kg, volumes per litre, and counts each. Returns the unit price of every item and which is cheapest. Source: https://hopi.co.uk/unit-price-calculator/
hopi_unix_timestamp_converter
Convert between Unix epoch timestamps and readable dates. Pass a timestamp to get the UTC and local date (seconds or milliseconds detected automatically), or pass a date (and optional time, interpreted in local time) to get the timestamp in seconds and milliseconds. Source: https://hopi.co.uk/unix-timestamp-converter/
hopi_upside_down_text
Flip text upside down using Unicode look-alike characters and reverse its order, so it reads as if rotated 180 degrees. Characters with no upside-down equivalent are kept as they are (but still reversed in position). Source: https://hopi.co.uk/upside-down-text/
hopi_url_encoder
Percent-encode or decode text for URLs. Component mode encodes every reserved character (right for a single query value); whole-URL mode leaves structural characters like / ? & alone (right for a complete address). Source: https://hopi.co.uk/url-encoder/
hopi_url_parser
Parse a URL into its parts: protocol, host, port, path, fragment, origin and every decoded query parameter. If no scheme is given, https:// is assumed for a bare domain. Source: https://hopi.co.uk/url-parser/
hopi_user_agent_parser
Parse a user agent string into its parts: browser and version, rendering engine, operating system and version, device type (mobile, tablet or desktop) and whether it looks like a bot or crawler. Uses an ordered pattern table (Edge before Chrome, Chrome before Safari). User agent strings can be spoofed, so results are best-effort, not proof. Source: https://hopi.co.uk/user-agent-parser/
hopi_username_generator
Invent memorable usernames by pairing a random adjective with a random noun, optionally with a two-digit number on the end. Returns a list of unique usernames. Source: https://hopi.co.uk/username-generator/
hopi_utm_link_generator
Add UTM campaign parameters (utm_source, utm_medium, utm_campaign, utm_term, utm_content) to a URL without breaking existing query parameters. Warns on mixed case and notes any missing core parameters. Only http and https URLs are accepted. Source: https://hopi.co.uk/utm-link-generator/
hopi_uuid_generator
Generate 1 to 100 random version 4 UUIDs using a cryptographically secure random source. Never uses Math.random. Source: https://hopi.co.uk/uuid-generator/
hopi_vat_calculator
Add UK VAT to a net amount, or remove VAT from a gross (VAT-inclusive) amount. Default rate is the UK standard 20 percent. Returns the net, VAT and gross figures. Source: https://hopi.co.uk/vat-calculator/
hopi_vigenere_cipher
Encode or decode text with the classic Vigenere cipher using a keyword. Each letter is shifted by the matching keyword letter (A is 0 to Z is 25), the keyword repeating across the message. Only A to Z letters are changed and case is preserved; numbers, spaces and punctuation pass through unchanged and do not advance the keyword. The keyword uses only its letters. Decoding reverses the shift. Source: https://hopi.co.uk/vigenere-cipher/
hopi_volume_converter
Convert a volume from one unit to another. Units: ml (millilitres), l (litres), ukpt (UK pints), ukgal (UK gallons), usgal (US gallons), ukfloz (UK fluid ounces), usfloz (US fluid ounces), m3 (cubic metres). Source: https://hopi.co.uk/volume-converter/
hopi_water_intake_calculator
Estimate a rough daily fluid target from body weight, using 30 to 35 ml per kg, plus an activity add (sedentary 0, light 250, moderate 500, active 750, very_active 1000 ml) and 500 ml more for hot conditions. Use units 'metric' (weightKg) or 'imperial' (weightStone and weightPounds). Returns a low-to-high range in litres, millilitres and 250 ml glasses. Source: https://hopi.co.uk/water-intake-calculator/
hopi_week_number
Find the ISO 8601 week number for a date. Dates use the YYYY-MM-DD format and default to today. ISO weeks run Monday to Sunday and week 1 holds the year's first Thursday. Returns the week number, ISO year, and the Monday and Sunday of that week. Source: https://hopi.co.uk/week-number/
hopi_weight_converter
Convert a weight from one unit to another. Units: g (grams), kg (kilograms), oz (ounces), lb (pounds), st (stone). Source: https://hopi.co.uk/weight-converter/
hopi_wheel_spinner
Spin a wheel of names or options and pick one at random. Every item has an equal chance. Returns the chosen item. Source: https://hopi.co.uk/wheel-spinner/
hopi_word_counter
Analyse a block of text and return the word count, character count (with and without spaces), sentence count, paragraph count and an estimated reading time at 225 words per minute. Source: https://hopi.co.uk/word-counter/
hopi_word_frequency_counter
Count how often each word appears in a block of text, sorted from most to least frequent. Returns the total word count, the number of unique words, and the top 20 words with their counts and percentages. Common stop words (the, and, of, ...) can optionally be ignored. Source: https://hopi.co.uk/word-frequency-counter/
hopi_working_days_calculator
Count the working days (Monday to Friday) between two dates, inclusive of both ends, optionally excluding England and Wales bank holidays. Dates use the YYYY-MM-DD format. Bank holiday data covers 2026 and 2027 only, so outside those years just weekends are excluded. Source: https://hopi.co.uk/working-days-calculator/
hopi_would_you_rather_generator
Draw original, family-friendly would-you-rather pairs, open icebreaker questions or rapid-fire this-or-that pairs, optionally filtered by category. Would-you-rather categories: silly, food, travel, work, deep, kids. Icebreaker categories: work, party, deep, kids. This-or-that has no categories. Returns distinct items drawn at random. Source: https://hopi.co.uk/would-you-rather-generator/
hopi_yes_no_wheel
Get a random yes or no decision, with an optional maybe. Returns the answer. Source: https://hopi.co.uk/yes-no-wheel/
hopi_zero_width_text_hider
Hide a secret message inside ordinary text using invisible zero-width Unicode characters, reveal a message hidden that way, or clean zero-width characters out of text. Mode 'hide' takes cover and secret (optional spread to distribute the invisible run between words) and returns the output text plus the number of invisible characters added (UTF-8 bytes x 4 + 1 end marker). Mode 'reveal' takes text and returns the decoded message, or an error if nothing is hidden. Mode 'clean' takes text and strips U+200B, U+200C, U+200D, U+2060, U+FEFF, U+180E and U+00AD, reporting how many were removed. This is hiding, not encryption. Source: https://hopi.co.uk/zero-width-text-hider/
Endpoints
| URL | Transport | State | Latency | Checked |
|---|---|---|---|---|
| https://mcp.hopi.co.uk/mcp | streamable-http | answering | 86 ms | 3 min ago |
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Hopi — questions
Answers built from our own checks of this server.
What can Hopi do?
It exposes 195 tools, read directly from the server on our last check. Among them: hopi_add_working_days, hopi_age_calculator, hopi_alcohol_unit_calculator, hopi_alphabetical_order, hopi_angle_converter, hopi_area_converter and 189 more. The full list with descriptions is on this page — we take it from the server itself via tools/list, not from a README.
How MCP servers expose tools in the first place →
Is Hopi working right now?
We send a real MCP handshake every 15 minutes. Over the last 24 hours 87 of 91 checks got a reply (95.6%), average response time 219 ms. The bar chart above shows every period we have measured.
How do I connect Hopi?
Copy the ready config from this page — we generate it for Claude Code, Claude Desktop, Codex, Cursor and VS Code, each with the file path that client actually reads. It is a remote server, so there is nothing to install — the client connects to the address.
Does Hopi need an API key?
No. Hopi completed a full MCP handshake with us as an anonymous client and listed its tools without asking for anything. All 195 of them are readable on this page. This is what we observed, not what the docs claim.
How fast is Hopi?
It answers our handshake in 219 ms on average, which is faster than 66% of all working MCP servers we measure. The comparison comes from our own checks across the whole registry, every 15 minutes.