Claude Skills
The open format is called Agent Skills and works in Claude Code, Codex, Cursor and other agents — most people know it as Claude Skills.
Every Agent Skill we could find on GitHub, deduplicated by content. 79 600 files from 1 763 authors, of which 61 947 are unique — the rest is the same skill repackaged into someone else's repository. For each one: what it weighs in tokens, whether it ships runnable scripts, and which MCP servers it needs.
Estimate a peer's clock offset from ping/pong round trips — take the peer's own processing time out before halving, weight each sample against the best round trip seen, insist the local time source is monotonic, and fall back to the uncorrected value while the estimate is not yet usable. Use when several devices must agree what time it is before they can agree where a stream is, when a group drifts apart on a congested network, or when a position correction jumps after the device adjusts its clock.
One `var xJob: Job?` field per concern, cancel-before-relaunch as an invariant at every launch site, and teardown writes wrapped so a cancellation cannot stop them halfway. Use when periodic updates arrive several times per tick, when stale results from a previous item overwrite the current one, or when a long-lived object keeps working after it was released.
Declaring a Launch Services environment dictionary (`LSEnvironment`) in a packaged macOS app's property list pins the process `PATH` to the four bare system directories, so every external process the app spawns loses everything installed elsewhere. Use before adding any environment variable to a macOS app bundle, when a helper the app shells out to reports "command not found" only for installed users, or when a feature that works from a terminal launch silently does nothing from the Dock.
Build a ranked mosaic (one big tile plus smaller ones) with an arm for every possible count, so no entry is silently dropped and no arrangement leaves an empty rectangle — plus one clip around the whole block rather than one per tile. Use when a "top five" shows four, when a grid renders a visible gap at some counts, or when an early return on an "unsupported" size looks harmless.
Put every conversion between transport payloads, domain models and persistence rows in dedicated files of pure extension functions — one direction per function, no suspending work, no logging, nothing else in the file — and keep the layer honest with a grep. Use when conversion code is spreading into data classes, data-access objects or service clients, when a field turns out to be holding a value that belongs to a different field, or when re-reading a row wipes a flag the user set.
Producing a native shared library a JVM app can actually load and ship — why a prebuilt portable bundle usually is not a loadable library at all, building on the oldest base system you support, run-path choice, which libraries to deliberately leave out of the bundle, and gating the build on a load-and-initialize smoke test. Reach for it when the bundled native works on every developer machine and fails on a clean one, or when you discover the app has been quietly using a system-wide copy instead of yours.
A top-level tab has to be registered in every navigation surface that holds its own copy of the tab list — bottom bar, rail, and a stylized bar that keeps two lists — plus the graph and the flag that gates it, or the tab exists in code and never renders. The same drift catches a status entry point carried by more than one top app bar, where the missing badge reads as "nothing is running" rather than as a bug. Covers why a tab's ordinal is an identity rather than a position, what a conditional tab needs when it disappears under the user, and why a badge dot needs a ring of the page colour. Use when a newly added tab or badge shows on one surface but not another, when selection highlights the wrong tab after reordering, or when a tab bar overflows once one more tab appears.
A child toggle gated by a parent condition must key its auto-disable effect on the parent's current value, grey out rather than hide when the gate is closed, and be gated again at the consumer — otherwise the child sticks ON with no way for the user to clear it. Use when a settings switch is stuck on, is greyed out while reading enabled, or keeps acting after its precondition is gone.
Decide whether a mid-size app needs an interactor or use-case tier at all, how a clean boundary survives without one (repository interfaces plus pure mapping functions), how to prove an absence rather than assume it, and the specific signal that says it is finally time to add the tier back. Use when the tier feels like typing with no payoff, when reviewing an architecture that has none, or when the same orchestration has been pasted into a third view model.
An empty or pass-through platform implementation in a multiplatform project means nobody wrote it, not that the platform cannot do it — check the dependency's resolved variants and the source set that declares it before telling anyone a feature is impossible there. Use when a feature "doesn't work on desktop/iOS", when a platform file returns its input unchanged or has an empty body, or before writing off a feature as a platform limit.
A now-playing artwork pager that both follows the player and drives it, without the two writing to each other in a loop — the in-progress-scroll flag covers programmatic animation as well as drags, the seek is dispatched from the settled page only, and the page-difference decision is a pure function outside the UI runtime. Use when a swipe bounces back to the page it came from, when one swipe skips two tracks, when the pager stops following the player after a fast swipe, when swiping backwards restarts the current track instead of going back one, or when a far swipe under shuffle lands on the wrong song.
Deliver a returning auth callback's token straight to session state and let the login screen close itself by observing the stored session — routing the token through navigation pushes a second login screen and the post-login close peels the wrong one. Use when a browser-based login succeeds but the user is left staring at the login screen.
A tokenizer, spellchecker or analyzer needs a multi-megabyte dictionary that would bloat every install for a feature most users leave off — fetch it once, on opt-in, into a plain directory, and make every consumer ask the filesystem "am I ready" rather than trust a flag. Use when a per-language asset inflates a package on only one target, when a half-downloaded asset must never look installed, or when a feature stays broken even after its download reports success.
Return a whole period's figures as one immutable snapshot from a single suspend call, rather than as a dozen independent flows the screen has to line up — a screen comparing two spans needs each span coherent, and separate emissions let a count from this period render beside a total from the last. Covers when a single-emission flow is a suspend function in costume, which derived figures belong on the snapshot, and why a rate needs the denominator a human means. Use when a comparison screen briefly shows mismatched numbers while reloading, when adding the tenth flow to one screen's repository, or when two places compute the same average differently.
Make one stored value mean the same thing on two unrelated audio backends by defining the band centres, the width and the range once, verifying both against a reference implementation instead of by ear, and declining the platform's built-in effect whose parameters vary per device. Use when a tone or gain setting is being added on more than one platform, or when the same saved setting sounds different on each.
An optional build-time dependency of a media engine may be missing from another platform's bundle, and the engine rejects the WHOLE chain string when one stage in it is unknown — so retry without the optional stage rather than losing the mandatory one, and return which tiers were accepted so callers never drive a stage that is not there. Use when a feature works on one platform's bundle and silently does nothing on another.
Map a sectioned API response as a list of (title, items) in the order it arrived, never by reading result[0] and result[1] into named fields — a signed-in account is recorded here as getting an extra section pushed in front, and any such shift mislabels every section after it and drops the last one with no error. Assume the set and order may also vary by locale or region, and capture two responses to find out. Use when modelling a home feed or browse screen made of shelves, or when a screen shows the right content under the wrong headings for some users only.
A palette generator that flips its state to Loading before its own suspension point reports no colour for the entire duration of every generation, and a generation cancelled part-way leaves it Loading with nothing to restart it — so any surface reading the palette directly paints its null fallback. Covers why the effect must be keyed on the bitmap alone (or on nothing at all), why a "already done" flag assigned after a suspension is not a record of done, and why the last resolved colour has to be held separately. Use when a screen tinted from artwork is sometimes right and sometimes black, when the same item tints correctly on one visit and not the next, or when a derived colour scheme silently sits on its fallback.
Splitting one file into N byte-range requests issued in parallel over a bare HTTP client, each chunk to its own temp file, merged in order, with progress reported through a channel-backed flow — plus when ranges are actually safe, how big a chunk should be, and why a failure retries one chunk rather than the file. Use when a large download is slower than the link allows, when a download restarts from zero after a hiccup, or when a progress bar sticks just short of full.
Build a browse tile whose cover art is tilted and runs off the clipped corner — the modifier order that makes the diagonal a cut rather than a pasted square, the rotated bounding-box growth that decides how much room siblings must leave, and why a non-square tile cannot size its decoration off the width. Use when a rotated image shows sliced corners, when text collides with tilted art or reflows the moment that art loads, or when a rotated child covers its neighbours instead of being clipped by its parent.
Apply per-track loudness normalisation with the platform's loudness enhancer when each track gets its own player — re-creating the effect per track because it stays attached to one audio session, skipping it while a remote-playback session is active, and clamping the gain that comes from metadata. Use when normalisation works on the first track and silently stops afterwards, when enabling it throws while nothing is playing, or when every other track in a queue comes out louder.
Model "asked, and not yet answered" as its own field, because without it a rejected request and a peer who simply has not looked at their screen are indistinguishable — both look like nothing happened. Covers the one set against many clears, clearing locally when no answer will ever come, and giving the user a way out. Use when an action appears to do nothing, when a screen can get stuck waiting forever, or when an error message has no place to appear.
Print the share of input a distribution could actually classify, computed with exactly the predicates that built the buckets, and keep that line reachable when coverage is zero. Use when a chart is built over a nullable join or a parsed text column, when the bars look plausible but the totals underneath disagree, or when the one case that most needs a disclaimer is the case that renders nothing.
Decide whether the freshly-loaded item should start, and where it should start, before you build it — then pass both into the load call, rather than loading with a hardcoded "start playing" and correcting it a moment later. Reach for it when a follower in a synchronised room bursts into sound in a session everyone else has paused, or when a newly loaded item audibly starts and then stops.
Build a periodic notifier that never misses an item when a run is delayed, and whose only way to repeat one is a kill inside a single narrow window. Covers keeping the "already handled" record in the database rather than in the worker, scanning a time window deliberately wider than the scheduling interval so a skipped run catches up, and processing oldest-first so an interrupted run loses the newest item rather than a random slice. Android only. Use when users report duplicate notifications after a device restart, when items are missed while the device is idle, or when a first run floods the user with the whole back catalogue.
One generic "load this item and start playing" function normalizes several item types into a single internal shape, routes the queue-seeding strategy off a discriminator, and gates every pre-enqueue policy at that one place. Use when playback can start from many screens and a rule (content filter, dedup, analytics, resume-without-autoplay) keeps getting forgotten on one of the paths.
Persisting and restoring the playback position cheaply — a full queue save on lifecycle edges versus a light five-second position tick that rides an existing loop, skipping the save while the queue is being rebuilt, and snapshotting values before issuing player commands that change them. Use when background playback resumes from the start of a track after the process is killed, or when a restore lands on the wrong track or position.
Keep a group of clients together by publishing the playhead with every command, correcting it for the time the command spent in flight, and seeking only when the local gap exceeds a tolerance — rather than by making everyone wait for the slowest member. Use when a synchronised session drifts audibly apart, when followers stutter continuously as they chase the source, or when each device resolves its own stream and therefore takes a different amount of time to be ready.
Derive "which preset is this" by comparing the presets against the value in force instead of storing a label beside it, so editing drops to Custom by itself and returning re-selects — and derive any per-preset field that is a function of the preset's own numbers rather than writing it out per row. Use when a preset picker keeps showing a stale name, when a preset never re-selects itself, or when a per-row constant has drifted in one row out of twenty.
Speak protobuf from shared Kotlin by annotating ordinary data classes with field numbers instead of generating a code layer — with the encoder setting that makes the bytes match a generated encoder, the equality override a byte-array field needs, and the conformance test that pins the equivalence. Use when a schema-driven protocol has to work on every target rather than only the JVM, when encoding a message with an absent nested field throws, or when round-trip tests pass while real peers reject the frames.
Build a seek control from a progress indicator plus a transparent pointer layer instead of from a slider — a hit box taller than the visual, drags consumed so an ancestor pager cannot steal a scrub, the drag's own fraction shown while interacting, a thumb drawn by you, and the separate decision of drawing an element closer without moving its layout slot. Use when the visual you need has no slider equivalent, when a scrub gets hijacked by a swipe or a sheet, when the bar jumps back mid-drag, or when a thin control is impossible to hit.
Every publisher in a shared session is edge-triggered off a change, so a participant who was already running when they took the publishing role emits nothing and the group sits in silence — publish a full snapshot on becoming the source, and again when a new member arrives. Use when a session starts empty until someone touches the transport, when a late joiner sees nothing, or when your state watchers all look correct and the group still knows nothing.
A player's "current index" is exposed to the UI but freezes on track change or highlights the wrong row once shuffle is on, because the engine's timeline order and the shuffled play order are two different index spaces. Use when the now-playing marker in a queue list is stuck, points one row off, or lights up every copy of a repeated track.
A rebuild-state flag on the queue marks "being rebuilt" versus "stable" (two operative values, whatever the enum declares), so re-entrant load requests return early and nothing snapshots the queue while it is half-built. Use when pagination fires twice for one scroll, when a restored queue comes back missing the track that was playing, or when a loading state never clears after an error.
Running a bytecode shrinker over a JVM desktop app — which optimization families must stay off and why, why obfuscation breaks the rendering and reflection layers, the keep-rule families a native-binding plus coroutines plus HTTP-client app needs, and how to feed the shrunk jars to the packager. Reach for it when the release build starts with a verification error, renders a see-through or blank surface, or fails only in the packaged installer while the development run is fine.
Read a build log by going to the bottom for the verdict and then to the FIRST error marker for the cause — never a fixed-size window from either end, because the causal message and the failure banner sit at opposite ends of the output. Use when a background build finishes and you are about to summarise it, when a log says only "task X FAILED" with no reason, or when a filter came back empty and you are about to call that a clean build.
Expose state through `asStateFlow()` rather than an upcast of the mutable holder, and turn a cold source flow hot with `stateIn(scope, WhileSubscribed(timeout), initial)` so it survives collector churn without running forever. Use when a screen re-queries its source on every rotation or navigation, when work continues after the last collector leaves, or when something outside the owner is writing state it should only be reading.
A barrier that holds a group until every member reports ready — answer it on bufferedness rather than on playing, answer only when you are actually named, name who is being waited for in the UI, and understand that one member that never answers freezes everyone. Use when a shared session stalls for all participants after one slow device joins, when playback silently never starts, or when a "loading" state has no explanation attached to it.
Build a small real-time IIR filter in pure Kotlin from the audio-EQ-cookbook formulas — low-pass, high-pass, or a bank of peaking sections — with cascaded stages for a steeper slope, independent state per channel, neutral stages that keep the state size fixed, and lazy coefficient recompute. Use when a sweepable filter is needed inside an audio callback, when a stereo filter collapses the stereo image, when the filter output is silence or NaN, or when sweeping a cutoff or dragging a band produces ticks.
Every bitmap a home-screen widget draws is copied into the RemoteViews payload handed across a process boundary, and the platform rejects an update whose bitmaps exceed a fixed budget — so decoding each image at the size it is drawn is not an optimisation, it is what keeps the widget on screen. Covers the pixel arithmetic that decides how many images fit, why the failure is invisible outside the system log, and why every surface reading the same image must agree on both its cache key and its decode size. Android only. Use when a widget shows the framework's error placeholder, when it renders on one device and not another, or when adding one more tile empties the whole widget.
Cache a large published index by parsing it into indexed rows once and re-checking it with the server's own ETag, so a routine freshness check costs a couple of hundred bytes — replaying the stored validator only while rows exist, treating a 200 that parses to nothing as a failure, and never letting a failed check refresh the timestamp. Use when a browsable catalogue is fetched from a static host, or when a cached index went empty and never refilled.
Delete a feature that duplicates a newer one — two effects on one output multiply — after auditing what else uses the handle the removed feature appeared to own, deleting the no-op stubs on the other platforms, and force-stopping before judging whether the removal worked, because an already-attached external effect outlives the change. Use when replacing a delegating integration with an in-app one, or when a removed feature still seems to be running.
One table of method shapes for a repository sitting over a local database plus a remote API — local reads as a cold flow moved onto the IO dispatcher, remote reads as a flow of a success/error envelope, writes as withContext. Use when adding methods to a repository, when reviewing one whose shapes have drifted apart, or when a screen sits on its loading state forever with nothing in the log.
An envelope family for repository results — a remote wrapper, a local wrapper with a loading state, and a payload-free variant — plus the wrap-side and collect-side helpers that stop every view model from hand-writing the same branch, where the mapping from transport model to domain model belongs, and the one thing the envelope must never swallow. Use when designing repository return types, when error handling has drifted apart between screens, or when a cancelled screen reports a failure it never had.
Ship prebuilt native libraries to a multiplatform desktop build by splitting bundling into two Gradle tasks with different homes — a dev-machine task that builds the slices, packs tarballs and prints their digests, and a CI task that only downloads and verifies against digests pinned in the build file; reach for it when CI needs a native toolchain it should not have, when a native bump quietly ships the previous binaries, or when the packaged installer launches with the native missing entirely.
The five stages a remote response passes through — transport model in a per-integration service module, a pure parser layer, a domain model, a result envelope, then collection — with the rule that each integration is its own module so one source's breakage cannot spread, and the placement rules that keep transport types out of screens. Use when adding a second remote source, when a UI file has started importing response classes, or when a screen shows a spinner forever after a response shape changed.
Gate an adaptive layout on the window's own width-versus-height, never on the platform, and flip every geometry value the gate owns in the same breath — frame sizing, content scale and scrim height. Use when a layout is right on a phone and wrong in a narrow or resized desktop window, when forcing an adaptive flag to one value breaks a different platform's screen, or when artwork swallows the whole page on a wide window.
Tell an opt-in marker from a restricted-to marker before adding suppressions — the first is enforced by the compiler and demands acknowledgement, the second demands nothing and means something different and worse; includes how to read which one an API carries straight out of the cached artifact, and why both conventions coexist in one library. Use when an `@OptIn` looks necessary but the same API compiles without it elsewhere, when the IDE offers a suppression for an annotation you have not read, or when deciding whether a library call is safe to depend on.
Give every reconnect loop exponential backoff, a ceiling, a class of failures it refuses to retry, and a lifecycle gate — then give the feature a health signal, because one that fails silently stays broken for months. Use when a background connection drains the battery, when a bad credential produces an endless reconnect, or when an integration quietly stopped working.
Set up one Room database shared across Android, JVM/desktop and iOS with an expect/actual builder per platform, a bundled SQLite driver chosen once at the injection site, and a per-architecture audit of the driver artifact. Use when adding Room to a Kotlin Multiplatform module, when one target fails at the first database connection while the others work, or when a target compiles but its generated database implementation is missing.
Keep a Room database upgradable after twenty-plus schema versions — declaring the whole graph of (from,to) edges instead of assuming users only ever hop one version, filling the gaps a generated migration cannot express, and recreating triggers idempotently in the on-open callback. Use when an upgrade from an old build reports no migration path, when a trigger exists on upgraded databases but not on fresh installs (or the reverse), or before shipping a schema change to a long-lived app.
When two nearly identical things behave differently, count the variables that still differ and run one swap-or-trade test that eliminates at least half of them, before writing any fix. Use when the same symptom has survived two or more attempted fixes, when one widget or screen or platform works and its near-twin sitting beside it does not, or when every attempt costs a slow build and somebody else's attention.
Turn a user-facing feature off for the duration of a mode with a runtime override on the component, never by writing the stored preference — a process death mid-mode would leave the user's real setting permanently changed. Use when entering a mode has to disable an existing feature, when a setting mysteriously turned itself off and stayed off, or when a mode's cleanup is the only thing standing between a user and a lost preference.
Two playback backends need opposite plumbing for the same setting — one whose per-stream consumers sample a shared field needs no push at all, one whose every new handle starts blank needs an explicit re-apply at each creation site. Use when a setting reaches the current track but not the next one, when it survives on one platform and not the other, or when a level set on several handles keeps reverting.
Inside a layout scope, a scope-extension composable of the same name wins over the top-level one — silently, since both compile — so a call written for the plain version gets the scoped version's defaults and layout behaviour; covers fully qualifying to force the top-level one, `this@Scope.` to force the scoped one, and why outer scopes still apply from inside a nested layout. Use when an appear/disappear animation expands or collapses its parent instead of fading in place, when a composable behaves differently after being moved into a column or row, or when a call resolves to an overload you did not choose.
Split one screen into a shell that owns every cross-look concern and a content layer that only renders, connected by two holders — a state snapshot and an actions bag — so adding a second look costs one branch instead of a parameter-list edit; covers why the holders are stable-but-not-immutable, what must stay in the shell, and what must not. Use when a screen has grown a second visual style, when a style switch resets the scroll position or the artwork page, when adding a look means editing a fifty-argument signature, or when a "shared" helper starts needing a per-style `if`.
Filtering a paging stream only ever searches the pages already loaded, so whether an item is findable depends on how far the user happened to scroll — the search must query the store and render as a sibling overlay, leaving the paged reader and its drag-reorder, in-place removal and scroll position untouched. Covers the debounce and minimum-length gate, why the escaping belongs one layer above the query, and the one case where filtering in memory is correct. Use when search misses items that are definitely there, when results change after scrolling, or before threading a second data source through a paged list.
Adding a "show pronunciation" or transliteration feature across many non-Latin scripts in a Kotlin Multiplatform module — without pulling in ICU — needs a per-script dispatch built on Unicode block ranges rather than a locale, one line at a time rather than one song at a time, and a hard line between scripts that reduce to a table and the one or two that need a real dictionary. Use when a transliteration result is guessed for the wrong language, an unsupported platform fails outright instead of falling back, or a line that mixes two scripts (an original lyric plus an English aside) picks the wrong one.
A small @Stable holder for multi-select in a Compose list — keyed by stable id rather than list position, with every mutation funnelled through one private method so a hard cap on the selection size cannot be bypassed, plus the toggle/clear/select-all semantics that make the two gestures read differently. Use when building bulk actions over a list, when selections drift onto the wrong rows after a reorder or a page load, or when a cap holds for tapping rows but not for select-all.
Why a raw-query DAO method runs on a read-only connection, so database compaction fails there with "attempt to write a readonly database" while a checkpoint on the same connection succeeds and hides the problem. Reach for it when a bulk delete frees no disk space, or when a raw statement reports a readonly database you clearly opened for writing.
Claude Skills — questions
Answers built from the skills we actually parsed.