Cloudflare D1 Skill for Claude

Cloudflare D1 Database

Status: Production Ready ✅ | Last Verified: 2025-01-15

Table of Contents

• What Is D1?
• Quick Start
• Critical Rules
• D1 API Methods
• Top 5 Use Cases
• Migrations Best Practices
• Common Patterns
• SQLite Type Affinity
• Top 5 Errors Prevented

What Is D1?

Cloudflare D1 is serverless SQLite on the edge:

• SQL database without servers
• Global distribution
• Zero cold starts
• Standard SQLite syntax
• Read replication for global performance

🆕 New in 2025

D1 received major updates throughout 2025:

Performance (January 2025)

• 40-60% latency reduction globally (P50 query times)
• Optimized SQLite engine for edge execution
• Reduced cold start impact for databases <100 MB

Reliability (September 2025)

• Automatic query retries: Read queries retry up to 2x on transient failures
• Transparent to application code (logged in wrangler tail)

Scalability (April 2025)

• Read Replication (Public Beta): Deploy read replicas globally
• Up to 2x read throughput for read-heavy workloads
• Sessions API for read-write separation

Compliance (November 2025)

• Data Localization: Specify EU/US jurisdiction for GDPR/data sovereignty
• Configure via --jurisdiction flag or wrangler.jsonc

⚠️ Breaking Change (February 10, 2025)

• Free tier hard limits enforced: 10 DBs, 500 MB each, 50 queries/invocation
• Exceeding limits = 429 errors (previously warnings only)
• Action: Review usage with wrangler d1 list and upgrade if needed

Full details: Load references/2025-features.md

Quick Start (5 Minutes)

1. Create Database

bunx wrangler d1 create my-database

Save the database_id from output!

2. Configure Binding

Add to wrangler.jsonc:

{
  "name": "my-worker",
  "main": "src/index.ts",
  "compatibility_date": "2025-10-11",
  "d1_databases": [
    {
      "binding": "DB",                    // env.DB
      "database_name": "my-database",
      "database_id": "<UUID>",
      "preview_database_id": "local-db"
    }
  ]
}

3. Create Migration

bunx wrangler d1 migrations create my-database create_users

Edit migrations/0001_create_users.sql:

CREATE TABLE IF NOT EXISTS users (
  user_id INTEGER PRIMARY KEY AUTOINCREMENT,
  email TEXT NOT NULL UNIQUE,
  username TEXT NOT NULL,
  created_at INTEGER NOT NULL
);

CREATE INDEX IF NOT EXISTS idx_users_email ON users(email);

PRAGMA optimize;

4. Apply Migration

# Local
bunx wrangler d1 migrations apply my-database --local

# Production
bunx wrangler d1 migrations apply my-database --remote

5. Query from Worker

import { Hono } from 'hono';

type Bindings = {
  DB: D1Database;
};

const app = new Hono<{ Bindings: Bindings }>();

app.get('/users/:email', async (c) => {
  const { results } = await c.env.DB.prepare(
    'SELECT * FROM users WHERE email = ?'
  )
    .bind(c.req.param('email'))
    .all();

  return c.json(results);
});

export default app;

Load references/setup-guide.md for complete walkthrough.

Critical Rules

Always Do ✅

• Use prepared statements with .bind() (never string concatenation)
• Create indexes for WHERE/JOIN/ORDER BY columns
• Use migrations for schema changes (never manual SQL)
• Batch queries for multiple operations (.batch())
• Run PRAGMA optimize after schema changes
• Handle errors explicitly (try/catch)
• Use INTEGER for timestamps (Date.now())
• Test locally before deploying migrations
• Use read replicas for global read performance

10. Validate input before SQL queries

Never Do ❌

• Never concatenate user input into SQL
• Never commit database_id to public repos
• Never skip migrations for schema changes
• Never use VARCHAR (use TEXT instead)
• Never skip indexes for filtered columns
• Never ignore SQLite type affinity rules
• Never use SELECT * without LIMIT
• Never run migrations without testing locally
• Never exceed 1MB per row

10. Never use DATETIME (use INTEGER for timestamps)

D1 API Methods

prepare() - Execute Queries

// Single result
const { results } = await env.DB.prepare(
  'SELECT * FROM users WHERE email = ?'
)
  .bind(email)
  .all();

// First result only
const user = await env.DB.prepare(
  'SELECT * FROM users WHERE user_id = ?'
)
  .bind(userId)
  .first();

// Raw results (faster)
const { results } = await env.DB.prepare(
  'SELECT username FROM users'
)
  .raw();  // Returns arrays instead of objects

batch() - Multiple Queries

const results = await env.DB.batch([
  env.DB.prepare('INSERT INTO users (email, username, created_at) VALUES (?, ?, ?)')
    .bind('[email protected]', 'user1', Date.now()),
  env.DB.prepare('INSERT INTO users (email, username, created_at) VALUES (?, ?, ?)')
    .bind('[email protected]', 'user2', Date.now()),
  env.DB.prepare('SELECT COUNT(*) as count FROM users')
]);

console.log('Users count:', results[2].results[0].count);

All queries execute in single transaction (all succeed or all fail).

exec() - Run SQL String

// For migrations/setup only
await env.DB.exec(`
  CREATE TABLE IF NOT EXISTS users (
    user_id INTEGER PRIMARY KEY,
    email TEXT NOT NULL
  );
  CREATE INDEX idx_email ON users(email);
`);

NEVER use for queries with user input!

Load references/query-patterns.md for complete API reference.

Top 5 Use Cases

Use Case 1: User CRUD

// Create
app.post('/users', async (c) => {
  const { email, username } = await c.req.json();

  const { results } = await c.env.DB.prepare(
    'INSERT INTO users (email, username, created_at) VALUES (?, ?, ?) RETURNING *'
  )
    .bind(email, username, Date.now())
    .all();

  return c.json(results[0]);
});

// Read
app.get('/users/:id', async (c) => {
  const user = await c.env.DB.prepare(
    'SELECT * FROM users WHERE user_id = ?'
  )
    .bind(c.req.param('id'))
    .first();

  if (!user) {
    return c.json({ error: 'Not found' }, 404);
  }

  return c.json(user);
});

// Update
app.patch('/users/:id', async (c) => {
  const { username } = await c.req.json();

  await c.env.DB.prepare(
    'UPDATE users SET username = ?, updated_at = ? WHERE user_id = ?'
  )
    .bind(username, Date.now(), c.req.param('id'))
    .run();

  return c.json({ success: true });
});

// Delete
app.delete('/users/:id', async (c) => {
  await c.env.DB.prepare(
    'DELETE FROM users WHERE user_id = ?'
  )
    .bind(c.req.param('id'))
    .run();

  return c.json({ success: true });
});

Use Case 2: Batch Operations

app.post('/users/bulk', async (c) => {
  const users = await c.req.json();  // Array of users

  const statements = users.map(user =>
    c.env.DB.prepare(
      'INSERT INTO users (email, username, created_at) VALUES (?, ?, ?)'
    ).bind(user.email, user.username, Date.now())
  );

  const results = await c.env.DB.batch(statements);

  return c.json({ inserted: results.length });
});

Use Case 3: Read Replication (Global Reads)

// Configure read replica (any region)
const session = c.env.DB.withSession({
  preferredRegion: 'auto'  // or 'weur', 'wnam', 'enam', 'apac'
});

// Read from nearest replica
const { results } = await session.prepare(
  'SELECT * FROM users WHERE email = ?'
)
  .bind(email)
  .all();

// Check which region served request
console.log('Served by:', results[0].served_by_region);

Load references/read-replication.md for complete guide.

Use Case 4: Transactions with Batch

// Transfer credits between users (atomic)
const results = await c.env.DB.batch([
  c.env.DB.prepare(
    'UPDATE users SET credits = credits - ? WHERE user_id = ?'
  ).bind(amount, fromUserId),
  c.env.DB.prepare(
    'UPDATE users SET credits = credits + ? WHERE user_id = ?'
  ).bind(amount, toUserId),
  c.env.DB.prepare(
    'INSERT INTO transactions (from_user, to_user, amount, created_at) VALUES (?, ?, ?, ?)'
  ).bind(fromUserId, toUserId, amount, Date.now())
]);

// All succeed or all fail (transaction)

Use Case 5: Pagination

app.get('/users', async (c) => {
  const page = parseInt(c.req.query('page') || '1');
  const limit = 20;
  const offset = (page - 1) * limit;

  const { results } = await c.env.DB.prepare(
    'SELECT * FROM users ORDER BY created_at DESC LIMIT ? OFFSET ?'
  )
    .bind(limit, offset)
    .all();

  return c.json({
    users: results,
    page,
    limit
  });
});

Migrations Best Practices

1. Always Use Migrations

bunx wrangler d1 migrations create my-database add_users_avatar

2. Make Migrations Idempotent

-- ✅ GOOD: Idempotent
CREATE TABLE IF NOT EXISTS users (...);
CREATE INDEX IF NOT EXISTS idx_email ON users(email);
DROP TABLE IF EXISTS old_table;

-- ❌ BAD: Fails on re-run
CREATE TABLE users (...);
CREATE INDEX idx_email ON users(email);

3. Test Locally First

bunx wrangler d1 migrations apply my-database --local
bunx wrangler d1 execute my-database --local --command "SELECT * FROM users"

4. Add PRAGMA optimize

-- End of migration
PRAGMA optimize;

Load templates/schema-example.sql for complete schema template.

When to Load References

Load references/setup-guide.md when:

• First-time D1 setup
• Creating first database
• Configuring bindings
• Applying first migration

Load references/query-patterns.md when:

• Need complete API reference
• Complex query patterns
• Batch operations
• Error handling

Load references/read-replication.md when:

• Setting up global reads
• Need low latency worldwide
• Understanding Sessions API
• Sequential consistency required

Load references/best-practices.md when:

• Optimizing query performance
• Schema design decisions
• Index strategies
• Production deployment checklist

Load references/limits.md when:

• Encountering 429 errors or quota warnings
• Planning capacity for free vs paid tiers
• Understanding database/query limits
• Migrating to paid plan

Load references/metrics-analytics.md when:

• Investigating performance issues
• Setting up monitoring and alerts
• Using wrangler d1 insights command
• Analyzing query efficiency

Load references/2025-features.md when:

• Upgrading from v2.x to v3.x
• Enabling new features (auto-retry, jurisdiction, replication)
• Understanding breaking changes (Feb 10, 2025 enforcement)
• Migrating before deadlines

Interactive Tools

Agents (Autonomous diagnostics):

• agents/d1-debugger.md: 9-phase diagnostic (config, migrations, queries, bindings, errors, limits, performance, Time Travel)
• agents/d1-query-optimizer.md: Performance analysis (slow queries, missing indexes, optimization recommendations)

Commands (Interactive wizards):

• commands/cloudflare-d1:setup.md: Interactive first-time setup wizard
• commands/d1-create-migration.md: Guided migration creation with validation

Using Bundled Resources

References (references/)

• setup-guide.md - Complete setup walkthrough
• query-patterns.md - Complete API reference with examples
• read-replication.md - Global read replicas setup
• best-practices.md - Performance and optimization

Templates (templates/)

• schema-example.sql - Complete schema with indexes
• d1-worker-queries.ts - All query patterns in Workers
• cloudflare-d1:setup-migration.sh - Complete setup script

Common Patterns

Error Handling

try {
  const { results } = await env.DB.prepare(
    'SELECT * FROM users WHERE email = ?'
  )
    .bind(email)
    .all();

  return c.json(results);
} catch (error) {
  console.error('D1 Error:', error);
  return c.json({ error: 'Database error' }, 500);
}

Raw Mode (Performance)

// Returns arrays instead of objects (faster)
const { results } = await env.DB.prepare(
  'SELECT user_id, email FROM users'
)
  .raw();

// results = [[1, '[email protected]'], [2, '[email protected]']]

COUNT Queries

const count = await env.DB.prepare(
  'SELECT COUNT(*) as count FROM users'
)
  .first('count');  // Get single column value

console.log('Total users:', count);

SQLite Type Affinity

D1 uses SQLite type affinity:

| Declared Type | Affinity |

|---------------|----------|

| INTEGER, INT | INTEGER |

| TEXT, VARCHAR, CHAR | TEXT |

| REAL, FLOAT, DOUBLE | REAL |

| BLOB | BLOB |

| (no type) | BLOB |

Best practices:

• Use INTEGER for numbers
• Use TEXT for strings (not VARCHAR)
• Use INTEGER for timestamps (Date.now())
• Use BLOB for binary data

Top 5 Errors Prevented

• SQL Injection: Use .bind(), never string concatenation
• Missing Indexes: Create indexes for WHERE/JOIN columns
• Migration Failures: Test locally first
• Type Confusion: Use INTEGER for timestamps
• Batch Size: Limit batch to <500 statements

Load references/best-practices.md for complete error prevention.

Secure Installation

When installing D1 driver packages, follow supply chain security best practices:

• Block post-install scripts — npm config set ignore-scripts true (or Bun: disabled by default)
• Cooldown period — Wait 7 days for new package versions to be vetted by the community
• Audit before installing — Run socket package score npm <pkg> or use socket npm install <pkg> to check packages

Load the dependency-upgrade skill for full security configuration including Socket CLI integration, cooldown setup, lockfile validation, and CI enforcement.

Official Documentation

• D1 Overview: https://developers.cloudflare.com/d1/
• Get Started: https://developers.cloudflare.com/d1/get-started/
• Client API: https://developers.cloudflare.com/d1/build-with-d1/d1-client-api/
• Read Replication: https://developers.cloudflare.com/d1/reference/read-replication/

Questions? Issues?

• Check references/setup-guide.md for setup
• Review references/query-patterns.md for API reference
• See references/read-replication.md for global reads
• Load references/best-practices.md for optimization