---

name: cloudflare-workers description: Optimize code for Cloudflare Workers free plan with 10ms CPU limit. Use when writing API routes, server code, middleware, or discussing performance optimization.

Cloudflare Workers Optimization

Constraints

• 10ms CPU limit on free plan (not wall-clock time)
• No heavy computation in request handlers
• No blocking operations

Patterns

Prefer Streaming

Copy// Good: Stream response
return new Response(readableStream, {
  headers: { 'Content-Type': 'application/octet-stream' },
});

// Bad: Buffer entire response
const data = await fetchAllData();
return new Response(JSON.stringify(data));

Delegate to Client

Move these to browser when safe:

• Image manipulation (canvas API)
• Complex calculations
• Data transformations
• Sorting/filtering large datasets

Efficient Algorithms

• Use early returns
• Avoid nested loops on large datasets
• Use Map/Set for O(1) lookups
• Paginate database queries

Async Patterns

Copy// Good: Parallel fetches
const [user, settings] = await Promise.all([getUser(id), getSettings(id)]);

// Bad: Sequential fetches
const user = await getUser(id);
const settings = await getSettings(id);

Response Caching

Copyreturn new Response(body, {
  headers: {
    'Cache-Control': 'public, max-age=3600',
    'CDN-Cache-Control': 'max-age=86400',
  },
});

Anti-patterns

• Synchronous crypto operations
• Large JSON parsing in hot paths
• Regex on untrusted input without limits
• Deep object cloning