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These docs are for Miniflare 2 which is no longer supported apart from critical security updates.
Please see the migration guide to upgrade to Miniflare 3, and the updated API docs.

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๐Ÿ’ป Using the CLI

The CLI is the easiest way to get started with Miniflare. It lets you start a local HTTP server that serves requests using your worker.


Miniflare is installed using npm:

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

You can also install and invoke the CLI using npx:

$ npx miniflare


If worker.js contains the following worker script:

addEventListener("fetch", (event) => {
event.respondWith(new Response("Hello Miniflare!"));

...running the following command will start a local HTTP server listening on port 8787 that responds with Hello Miniflare! to all requests:

$ miniflare worker.js
[mf:inf] Worker reloaded! (97B)
[mf:inf] Listening on :8787
[mf:inf] -

Note that the uncompressed size of the worker, 97B, is logged. Cloudflare requires all workers are under 1MiB once compressed. Miniflare will warn you when your uncompressed size exceeds 1MiB.

Watching and Debugging

Add --watch/-w and --debug/-d flags to reload the worker whenever worker.js changes and log debug information (including processed options) respectively:

$ miniflare worker.js --watch --debug
[mf:dbg] Options:
[mf:dbg] - Script Path: worker.js
[mf:dbg] Enabled Compatibility Flags: <none>
[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] -

Configuration Autoloading

Note that .env, package.json and wrangler.toml files are also being watched. These files are always loaded automatically and configure your worker's environment in addition to the CLI flags. See the Wrangler Configuration reference below for more details, but as an example, with the following wrangler.toml file and worker.js files:

KEY = "value"
addEventListener("fetch", (event) => {
event.respondWith(new Response(KEY));

...the local HTTP server would respond with value to all requests. The Guide goes into more detail on configuring specific features. To load a different wrangler.toml file, use the --wrangler-config/-c flag:

$ miniflare worker.js --wrangler-config wrangler.other.toml

To change the directory these default files are resolved relative to, use the --root flag:

$ miniflare api/worker.js --root api
# Miniflare will look for api/.env, api/package.json and api/wrangler.toml

Script Requirement

The only required option is the script to run. This can either be passed as a command line argument as we've been doing so far, in a wrangler.toml file or in a package.json file. The command line argument takes priority, then the script in wrangler.toml, then the main or module field in package.json (depending on whether modules support is enabled):

dir = "" # Defaults to "dist"
main = "./worker.js"
"main": "worker.js", // "service-worker" format
"module": "worker.mjs" // "modules" format

Request#cf Object

For a more accurate development experience, Miniflare automatically fetches the cf object for incoming requests (containing IP and location data) from a trusted Cloudflare endpoint, caching it for 30 days. You can disable this behaviour, falling back to a default cf object, using the --no-cf-fetch flag:

$ miniflare worker.js --no-cf-fetch

HTTPS Server

By default, Miniflare starts an HTTP server. To start an HTTPS server instead, set the https option. To use an automatically generated self-signed certificate, use the --https flag. This certificate is cached and will be valid for 30 days. The certificate will be renewed if it expires in less than 2 days:

$ miniflare worker.js --https # Cache certificate in ./.mf/cert
$ miniflare worker.js --https ./cert_cache # Cache in ./cert_cache instead

To use an existing certificate instead, use the --https-key, --https-cert, --https-ca and --https-pfx flags to set the paths to it. If these are encrypted, use the --https-passphrase flag to set the passphrase:

$ miniflare worker.js --https-key ./key.pem --https-cert ./cert.pem

Opening the Browser

Add the --open/-O flag to automatically open your default browser to the worker, once the HTTP server has started:

$ miniflare worker.js --open # Opens http://localhost:8787
$ miniflare worker.js --open # Opens


Add the --repl flag to start an interactive REPL session. This behaves exactly like the Node.js REPL, except you have access to Workers Runtime APIs instead. Any other Miniflare flag can be used too, with .env, package.json and wrangler.toml files automatically loaded. Specifying a script is optional when --repl is enabled, but may be required if you're using Durable Objects. If you're using an ES module format worker, bindings will be accessible via the env global variable.

The REPL can be configured using environment variables similar to Node.js:

  • MINIFLARE_REPL_HISTORY: path to save REPL history to. Setting this to an empty string disables persistent REPL history. Defaults to ~/.mf_repl_history.
  • MINIFLARE_REPL_HISTORY_SIZE: number of history lines to save if persistent REPL history is enabled. Defaults to 1000.
  • MINIFLARE_REPL_MODE: either sloppy or strict. Defaults to sloppy allowing non-strict code to run.
$ miniflare --repl --kv TEST_NAMESPACE
> await new HTMLRewriter().on("p", {
... element(e) {
..... e.setInnerContent("new");
..... }
... }).transform(new Response("<p>old</p>")).text()
> await env.TEST_NAMESPACE.put("key", "value")
> await env.TEST_NAMESPACE.get("key")

Update Checker

The CLI includes an automatic update checker that looks for new versions of Miniflare once a day. As Cloudflare are always improving and tweaking workers, you should aim to install these promptly for improved compatibility with the real Workers environment. You can disable this with the --no-update-check flag.



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]
--usage-model Usage model (bundled by default) [string]
-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]
--repl Enable interactive REPL [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 [boolean]
--actual-time Always return correct time from Date methods [boolean]
--inaccurate-cpu Log inaccurate CPU time measurements [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 [boolean/string]
optional cert path)
--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 [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]
R2 Options:
-r, --r2 R2 bucket to bind [array]
--r2-persist Persist R2 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 [boolean/string]
optional path)
--(no-)do-alarms Enable Durable Object alarms (enabled by [boolean]
Cache Options:
--(no-)cache Enable default/named caches (enabled by [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]
--text-blob Text blob to bind [array:NAME=PATH]
--data-blob Data blob to bind [array:NAME=PATH]
-S, --service Mounted service to bind [array:NAME=MOUNT[@ENV]]

Wrangler Configuration

Miniflare uses the default Wrangler configuration keys for most of its features. For Miniflare specific options, the keys are in the special [miniflare] section.

name = "worker" # --name
compatibility_date = "2021-11-12" # --compat-date
compatibility_flags = [ # --compat-flag
kv_namespaces = [ # --kv
{ binding = "TEST_NAMESPACE", id = "", preview_id = "" }
r2_buckets = [ # --r2
{ binding = "BUCKET", bucket_name = "" }
bindings = [ # --do
{ name = "OBJECT", class_name = "Object" }
[vars] # --binding
KEY = "value"
bucket = "./public" # --site
include = ["upload_dir"] # --site-include
exclude = ["ignore_dir"] # --site-exclude
crons = ["30 * * * *"] # --cron
command = "npm run build" # --build-command
cwd = "build_cwd" # --build-base-path
watch_dir = "build_watch_dir" # --build-watch-path
format = "modules" # --modules
dir = "worker"
main = "./index.mjs" # [script]
[[build.upload.rules]] # --modules-rule
type = "ESModule"
globs = ["**/*.js"]
[wasm_modules] # --wasm
MODULE = "module.wasm"
[text_blobs] # --text-blob
TEXT = "text.txt"
[data_blobs] # --data-blob
DATA = "data.bin"
host = "" # --host
port = 1337 # --port
upstream = "" # --upstream
watch = true # --watch
live_reload = true # --live-reload
env_path = ".env.test" # --env
kv_persist = true # --kv-persist
r2_persist = true # --r2-persist
cache_persist = "./cache" # --cache-persist
cache = false # --no-cache
durable_objects_persist = true # --do-persist
durable_objects_alarms = false # --no-do-alarms
update_check = false # --no-update-check
cf_fetch = "./cf.json" # --cf-fetch ./cf.json
cf_fetch = false # --no-cf-fetch
https = true # --https
https = "./cert_cache" # --https ./cert_cache
actual_time = true # --actual-time
global_async_io = true # --global-async-io
global_timers = true # --global-timers
global_random = true # --global-random
actual_time = true # --actual-time
inaccurate_cpu = true # --inaccurate-cpu
key = "./key.pem" # --https-key
cert = "./cert.pem" # --https-cert
ca = "./ca.pem" # --https-ca
pfx = "./pfx.pfx" # --https-pfx
passphrase = "pfx passphrase" # --https-passphrase
[miniflare.globals] # --global
KEY = "value"
[miniflare.mounts] # --mount
api = "./api"