Miniflare

Last updated Oct 18, 2026 Use Wrangler for most projects

This documentation describes the Miniflare API, which is only relevant for advanced use cases. Most users should use Wrangler to build, run, and deploy their Workers.

Miniflare is a simulator for developing and testing Cloudflare Workers ↗︎. It is written in TypeScript and uses a local workerd process to implement Workers runtime APIs.

Miniflare is not a hardened sandbox

Do not use Miniflare to run untrusted or potentially malicious Worker code directly on your machine. Run the entire development process inside an appropriate secure sandbox, such as a virtual machine.

Miniflare starts a local workerd ↗︎ process. This warning applies to default local execution with wrangler dev, vite dev, vite preview, direct Miniflare use, and Miniflare-based testing tools. Setting remote: true on a binding changes which resource your code accesses, but your Worker code still executes locally. By contrast, legacy wrangler dev --remote executes your Worker code on Cloudflare.

Miniflare is not a security boundary for untrusted code. Although workerd attempts to restrict Worker code to configured resources, an implementation bug could allow code to escape those restrictions. The hosted Workers platform applies additional layers of defense in depth that Miniflare does not provide locally.

  • 🎉 Fun: develop Workers easily with detailed logging, file watching and pretty error pages supporting source maps.
  • 🔋 Full-featured: supports most Workers features, including KV, Durable Objects, WebSockets, modules and more.
  • ⚡ Fully-local: test and develop Workers without an Internet connection. Reload code on change quickly.

Get Started GitHub NPM

These docs primarily cover Miniflare specific things. For more information on runtime APIs, refer to the Cloudflare Workers docs.

If you find something that doesn't behave as it does in the production Workers environment (and this difference isn't documented), or something's wrong in these docs, please open a GitHub issue ↗︎.

  • Get Started: Install and configure the Miniflare API to dispatch events and test Cloudflare Workers locally.
  • Writing tests: Write integration tests against Workers using Miniflare.
  • Core: Core Miniflare features for testing Cloudflare Workers, including fetch events and compatibility settings.
  • Developing: Development tools for Miniflare, including debugger support and live reload for Cloudflare Workers.
  • Migrations: Review migration guides for specific versions of Miniflare.
  • Storage: Configure and manage local storage simulators in Miniflare for Workers bindings like KV, R2, and D1.

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description: Configure compatibility dates and flags in Miniflare to match Cloudflare Workers runtime behavior. title: Compatibility Dates image: https://developers.cloudflare.com/workers/testing/miniflare/core/compatibility/og.png?v=67f291bf4d98026d

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