🔥 Miniflare

Miniflare is a simulator for developing and testing Cloudflare Workers.

🎉 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.

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

See https://miniflare.dev for more detailed documentation.

Features

📨 Fetch Events (with HTTP(S) server and manual dispatch)
⏰ Scheduled Events (with cron triggering and manual dispatch)
🔑 Variables and Secrets with .env Files
📚 Modules Support
📦 KV (with optional persistence)
✨ Cache (with optional persistence)
📌 Durable Objects (with optional persistence)
🌐 Workers Sites
✉️ WebSockets
🛠 Custom & Wrangler Builds Support
⚙️ WebAssembly Support
🗺 Source Map Support
🕸 Web Standards: Base64, Timers, Fetch, Encoding, URL, Streams, Crypto
📄 HTMLRewriter
👀 Automatic Reload on File Changes
💪 Written in TypeScript

Install

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] - http://127.0.0.1:8787

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]

Options:
  -h, --help              Show help                                    [boolean]
  -v, --version           Show version number                          [boolean]
  -H, --host              HTTP server host to listen on (all by default)[string]
  -p, --port              HTTP server port (8787 by default)            [number]
  -d, --debug             Log debug messages                           [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 (TYPE=GLOB)                [array]
      --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  [string]
  -w, --watch             Watch files for changes                      [boolean]
  -u, --upstream          URL of upstream origin                        [string]
  -t, --cron              Cron pattern to trigger scheduled events with  [array]
  -k, --kv                KV namespace to bind                           [array]
      --kv-persist        Path to persist KV data to (omit path for default)
      --cache-persist     Path to persist cached data to (omit path for default)
      --disable-cache     Disable caching with default/named caches    [boolean]
  -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]
  -o, --do                Durable Object to bind (NAME=CLASS)            [array]
      --do-persist        Path to persist Durable Object data to (omit path for
                          default)
  -e, --env               Path to .env file                             [string]
  -b, --binding           Bind variable/secret (KEY=VALUE)               [array]
      --wasm              WASM module to bind (NAME=PATH)                [array]
      --https             Enable self-signed HTTPS
      --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]
      --disable-updater   Disable update checker                       [boolean]

Acknowledgements

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 me understand this.