Fun, full-featured, fully-local simulator for Cloudflare Workers

Usage no npm install needed!

<script type="module">
  import miniflare from '';


πŸ”₯ Miniflare

Miniflare is a simulator for developing and testing Cloudflare Workers.

  • πŸŽ‰ Fun: develop workers easily with detailed logging, file watching and pretty error pages supporting source maps.
  • πŸ”‹ 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.

It's an alternative to wrangler dev, written in TypeScript, that runs your workers in a sandbox implementing Workers' runtime APIs.

See for more detailed documentation.


  • πŸ“¨ Fetch Events (with HTTP(S) server and manual dispatch)
  • ⏰ Scheduled Events (with cron triggering and manual dispatch)
  • πŸ”‘ Variables and Secrets with .env Files
  • πŸ“š Modules Support
  • πŸ“¦ KV (with optional persistence)
  • ✨ Cache (with optional persistence)
  • πŸ“Œ Durable Objects (with optional persistence)
  • 🌐 Workers Sites
  • βœ‰οΈ WebSockets
  • πŸ›  Custom & Wrangler Builds Support
  • βš™οΈ WebAssembly Support
  • πŸ—Ί Source Map Support
  • πŸ•Έ Web Standards: Base64, Timers, Fetch, Encoding, URL, Streams, Crypto
  • πŸ“„ HTMLRewriter
  • ⚑️ Live Reload on File Changes
  • πŸ“… Compatibility Dates/Flags Support
  • πŸ”Œ Multiple Workers Support
  • 🀹 Custom Jest Environment (with isolated per-test storage)
  • πŸ’ͺ Written in TypeScript


Miniflare is installed using npm:

$ npm install -g miniflare # either globally..
$ npm install -D miniflare # ...or as a dev dependency

Using the CLI

$ miniflare worker.js --watch --debug
[mf:dbg] Options:
[mf:dbg] - Scripts: worker.js
[mf:dbg] Reloading worker.js...
[mf:inf] Worker reloaded! (97B)
[mf:dbg] Watching .env, package.json, worker.js, wrangler.toml...
[mf:inf] Listening on :8787
[mf:inf] -

Using the API

import { Miniflare } from "miniflare";

const mf = new Miniflare({
  script: `
  addEventListener("fetch", (event) => {
    event.respondWith(new Response("Hello Miniflare!"));
const res = await mf.dispatchFetch("http://localhost:8787/");
console.log(await res.text()); // Hello Miniflare!

CLI Reference

Usage: miniflare [script] [options]

Core Options:
 -h, --help              Show help                                                   [boolean]
 -v, --version           Show version number                                         [boolean]
 -c, --wrangler-config   Path to wrangler.toml                                        [string]
     --wrangler-env      Environment in wrangler.toml to use                          [string]
     --package           Path to package.json                                         [string]
 -m, --modules           Enable modules                                              [boolean]
     --modules-rule      Modules import rule                                 [array:TYPE=GLOB]
     --compat-date       Opt into backwards-incompatible changes from                 [string]
     --compat-flag       Control specific backwards-incompatible changes               [array]
 -u, --upstream          URL of upstream origin                                       [string]
 -w, --watch             Watch files for changes                                     [boolean]
 -d, --debug             Enable debug logging                                        [boolean]
 -V, --verbose           Enable verbose logging                                      [boolean]
     --(no-)update-check Enable update checker (enabled by default)                  [boolean]
     --root              Path to resolve files relative to                            [string]
     --mount             Mount additional named workers                [array:NAME=PATH[@ENV]]
     --name              Name of service                                              [string]
     --route             Route to respond with this worker on                          [array]
     --global-async-io   Allow async I/O outside handlers                            [boolean]
     --global-timers     Allow setting timers outside handlers                       [boolean]
     --global-random     Allow secure random generation outside handlers             [boolean]

HTTP Options:
 -H, --host              Host for HTTP(S) server to listen on                         [string]
 -p, --port              Port for HTTP(S) server to listen on                         [number]
 -O, --open              Automatically open browser to URL                    [boolean/string]
     --https             Enable self-signed HTTPS (with optional cert path)   [boolean/string]
     --https-key         Path to PEM SSL key                                          [string]
     --https-cert        Path to PEM SSL cert chain                                   [string]
     --https-ca          Path to SSL trusted CA certs                                 [string]
     --https-pfx         Path to PFX/PKCS12 SSL key/cert chain                        [string]
     --https-passphrase  Passphrase to decrypt SSL files                              [string]
     --(no-)cf-fetch     Path for cached Request cf object from Cloudflare    [boolean/string]
     --live-reload       Reload HTML pages whenever worker is reloaded               [boolean]

Scheduler Options:
 -t, --cron              CRON expression for triggering scheduled events               [array]

Build Options:
 -B, --build-command     Command to build project                                     [string]
     --build-base-path   Working directory for build command                          [string]
     --build-watch-path  Directory to watch for rebuilding on changes                  [array]

KV Options:
 -k, --kv                KV namespace to bind                                          [array]
     --kv-persist        Persist KV data (to optional path)                   [boolean/string]

Durable Objects Options:
 -o, --do                Durable Object to bind                     [array:NAME=CLASS[@MOUNT]]
     --do-persist        Persist Durable Object data (to optional path)       [boolean/string]

Cache Options:
     --(no-)cache        Enable default/named caches (enabled by default)            [boolean]
     --cache-persist     Persist cached data (to optional path)               [boolean/string]

Sites Options:
 -s, --site              Path to serve Workers Site files from                        [string]
     --site-include      Glob pattern of site files to serve                           [array]
     --site-exclude      Glob pattern of site files not to serve                       [array]

Bindings Options:
 -e, --env               Path to .env file                                            [string]
 -b, --binding           Binds variable/secret to environment                [array:KEY=VALUE]
     --global            Binds variable/secret to global scope               [array:KEY=VALUE]
     --wasm              WASM module to bind                                 [array:NAME=PATH]


Miniflare was created by Brendan Coll.

Many thanks to dollarshaveclub/cloudworker and gja/cloudflare-worker-local for inspiration.

Durable Object's transactions are implemented using Optimistic Concurrency Control (OCC) as described in "On optimistic methods for concurrency control." ACM Transactions on Database Systems. Thanks to Alistair O'Brien for helping the Miniflare creator understand this.