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Workers Best Practices

Reviews and authors Cloudflare Workers code against production best practices. Load when writing new Workers, reviewing Worker code, configuring wrangler.jsonc, or checking for common Workers anti-patterns (streaming, floating promises, global state, secrets, bindings, observability). Biases towards retrieval from Cloudflare docs over pre-trained knowledge.

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SKILL.md

workers-best-practices

Your knowledge of Cloudflare Workers APIs, types, and configuration may be outdated. Prefer retrieval over pre-training for any Workers code task — writing or reviewing.

Retrieval Sources

Fetch the latest versions before writing or reviewing Workers code. Do not rely on baked-in knowledge for API signatures, config fields, or binding shapes.

Source	How to retrieve	Use for
Workers best practices	Fetch `https://developers.cloudflare.com/workers/best-practices/workers-best-practices/`

3 files · 31 KB7 KB

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Version history

Rule	Summary
Compatibility date	Set `compatibility_date` to today on new projects; update periodically on existing ones
nodejs_compat	Enable the `nodejs_compat` flag — many libraries depend on Node.js built-ins
wrangler types	Run `wrangler types` to generate `Env` — never hand-write binding interfaces
Secrets	Use `wrangler secret put`, never hardcode secrets in config or source
wrangler.jsonc	Use JSONC config for non-secret settings — newer features are JSON-only

Rule	Summary
Streaming	Stream large/unknown payloads — never `await response.text()` on unbounded data
waitUntil	Use `ctx.waitUntil()` for post-response work; do not destructure `ctx`

Rule	Summary
Bindings over REST	Use in-process bindings (KV, R2, D1, Queues) — not the Cloudflare REST API
Queues & Workflows	Move async/background work off the critical path
Service bindings	Use service bindings for Worker-to-Worker calls — not public HTTP
Hyperdrive	Always use Hyperdrive for external PostgreSQL/MySQL connections

Rule	Summary
No global request state	Never store request-scoped data in module-level variables
Floating promises	Every Promise must be `await`ed, `return`ed, `void`ed, or passed to `ctx.waitUntil()`

Rule	Summary
Web Crypto	Use `crypto.randomUUID()` / `crypto.getRandomValues()` — never `Math.random()` for security
No passThroughOnException	Use explicit try/catch with structured error responses

Workers Best Practices

Retrieval Sources

FIRST: Fetch Latest References

Reference Documentation

Rules Quick Reference

Configuration

Request & Response Handling

Architecture

Observability

Code Patterns

Security

Anti-Patterns to Flag

Review Workflow

Scope

Principles

Anti-pattern	Why it matters
`await response.text()` on unbounded data	Memory exhaustion — 128 MB limit
Hardcoded secrets in source or config	Credential leak via version control
`Math.random()` for tokens/IDs	Predictable, not cryptographically secure
Bare `fetch()` without `await` or `waitUntil`	Floating promise — dropped result, swallowed error
Module-level mutable variables for request state	Cross-request data leaks, stale state, I/O errors
Cloudflare REST API from inside a Worker	Unnecessary network hop, auth overhead, added latency
`ctx.passThroughOnException()` as error handling	Hides bugs, makes debugging impossible
Hand-written `Env` interface	Drifts from actual wrangler config bindings
Direct string comparison for secret values	Timing side-channel — use `crypto.subtle.timingSafeEqual`
Destructuring `ctx` (`const { waitUntil } = ctx`)	Loses `this` binding — throws "Illegal invocation" at runtime
`any` on `Env` or handler params	Defeats type safety for all binding access
`as unknown as T` double-cast	Hides real type incompatibilities — fix the design
`implements` on platform base classes (instead of `extends`)	Legacy — loses `this.ctx`, `this.env`. Applies to DurableObject, WorkerEntrypoint, Workflow
`env.X` inside platform base class	Should be `this.env.X` in classes extending DurableObject, WorkerEntrypoint, etc.