# Firenook: A faster drop-in for the Firebase emulators

> Firenook runs the Firebase emulators with your firebase.json, SDKs and ports: 40× faster writes, 10× less memory, no Java, and data that survives restarts.

[0.2.0 What’s new](https://firenook.dev/changelog/0.2.0)

Keep your `firebase.json`, SDKs and ports, and change one word in your script. No Java to install, and your data survives restarts.

`npm install --save-dev firenook`

[Get started](https://firenook.dev/docs/get-started/install)

- 40×

  faster writes 5.1 ms against 208.2 ms, median

- 10×

  less memory 2.11 GiB against 22.57 GiB at peak

- 0.59 s

  to restart with your data against 30.8 s

Firenook’s own screen, recorded from 0.2.0 on a demo shop: it starts with the 1.2 million documents, 64,000 users and 5,400 files it kept from its last run, takes two orders, and shows a webhook that fails, with its stack trace.

## Change one word

Same flags, same ports, same export format. Your project stays as it is, and firebase-tools stays for deploying.

package.json

```
-  "emulators": "firebase emulators:start --import ./data"
+  "emulators": "firenook emulators:start --import ./data"
```

- ### firebase.json and .firebaserc

  Read the way the Firebase CLI reads them.

- ### Rules, indexes, Functions

  Your code and config stay as they are.

- ### Your SDKs

  connectFirestoreEmulator, FIRESTORE_EMULATOR_HOST and the rest connect unchanged.

- ### Your data

  Imports and exports the official format, both ways.

## Eight emulators, on the ports you already use

Your SDKs connect to them as they connect to Google’s: the same hosts, the same ports, the same environment variables.

### [Firestore](https://firenook.dev/firestore-emulator)

8080

Native and web SDKs, realtime listeners, Security Rules, named databases, and the official import and export.

_Firestore after the run: the orders collection with two documents, the first open_

### [Authentication](https://firenook.dev/compatibility#auth)

9099

Every operation of the official Auth emulator: password, email link, phone, MFA, passkeys, tenants and blocking functions.

_Authentication after the run: three users_

### [Cloud Storage](https://firenook.dev/compatibility#storage)

9199

The Firebase and Cloud Storage APIs, with Security Rules evaluated natively, `firestore.get()` included.

_Cloud Storage after the run: three product pictures in the products folder_

### [Cloud Functions](https://firenook.dev/compatibility#functions)

5001

HTTP, callable and streaming functions, and every trigger: Firestore, Storage, Auth, Pub/Sub, Eventarc, schedules and task queues. Code reloads on save.

_Cloud Functions after the run: five calls, the newest a webhook that failed with a 500_

### [Pub/Sub](https://firenook.dev/pubsub-emulator)

8085

Every RPC over gRPC and HTTP/JSON: push, ordering, filters, dead-letter topics, seek, snapshots and schemas.

nightlyReport, every day 02:00: next run 2026-10-24 02:00 UTC

### [Cloud Tasks](https://firenook.dev/compatibility#tasks)

9499

Queues for onTaskDispatched, with the official retry and rate-limit behaviour.

### [Eventarc](https://firenook.dev/compatibility#eventarc)

9299

Custom events delivered to onCustomEventPublished, and the Firebase services’ own.

### [Extensions](https://firenook.dev/compatibility#extensions)

5001

Extensions from local, vendored or registry sources, offline once vendored.

The orders, users, files and calls above are from a run of the demo project, as Firenook returned them. Realtime Database, Hosting, App Hosting and Data Connect are not emulated; a `firebase.json` that configures them still starts, with a warning. [What each service covers](https://firenook.dev/compatibility).

## Measured on a real application

Two hours of a production app’s traffic against each emulator in turn, every operation timed by the client.

### Memory at peak

10× less

- Official

  22.6 GiB

- Firenook

  2.11 GiB

### Write, median

40× faster

- Official

  208 ms

- Firenook

  5.1 ms

### Listener update, median

19× faster

- Official

  209 ms

- Firenook

  11 ms

### Restart with data kept

52× sooner

- Official

  30.8 s

- Firenook

  0.59 s

### orderBy, limit 20

8× faster

- Official

  96.3 ms

- Firenook

  12.0 ms

### CPU over two hours

61% less

- Official

  1,586 s

- Firenook

  616 s

The app holds 211,205 Firestore documents and 6.7 GB in Storage; both emulators ran on one server. Firenook answered 25 of 26 query shapes faster and tied on the last. [How it was measured](https://firenook.dev/benchmarks).

## Your data stays where you left it

Add `--keep-data` and Firestore, Auth and Storage come back with all your data in about half a second, even with millions of documents. No export at every stop, no import at every start.

A crash loses at most the last second of writes, where the official emulator loses everything since its last export. A stop always closes the data cleanly.

`npx firenook emulators:start --keep-data`

Official emulator

Stop: export, 50–57 s Start: import, 21.6–23.6 s

Firenook

Stop, 0.04–0.30 s Start, 0.54–0.57 s

Stopping with the data saved, then starting again with it, on one time scale. The dim blocks are the spread between the fastest and the slowest runs.

```
$ npx firenook emulators:exec "node --test checkout.test.mjs"
firenook: Starting emulators: auth, functions, firestore, pubsub, storage
firenook functions: Loaded functions definitions from source: checkout, sendReceipt, stripeWebhook, nightlyReport.
All emulators ready
✔ checkout takes an order (173.227708ms)
ℹ pass 1
ℹ fail 0
firenook suite stopped cleanly
```

exit 0 **1.39 s** from start to stop, the test included

A run of the demo project’s test through firenook emulators:exec on firenook 0.2.0, with some lines left out.

## Run your tests against it

`emulators:exec` starts the suite, runs your command once everything is ready, with the emulator variables set, then stops and passes on the exit code.

CI gets plain lines, the same ones the official emulator prints, and there is no Java to set up first. Firenook needs only Node 24.

`npx firenook emulators:exec "npm test"`

## The console the Firebase emulators should have had

Google’s Emulator UI has no page for your Functions, Pub/Sub, Cloud Tasks or Eventarc, only a log. Firenook’s console covers every service it runs, live, on the Emulator UI’s port.

Every call, with what triggered it, its outcome, its duration and its logs.

![The console’s function calls: every call with its time, function, trigger, summary, outcome and duration, one of them a 500](https://firenook.dev/_astro/invocations-dark.CWGnqWbs_Z9SmY8.webp)

Light and dark, works offline, sends nothing anywhere. Bookmarks to the official UI’s pages open the matching console page. [Every page of the console](https://firenook.dev/console).

## Give your agent the emulator, not production

`firenook mcp` gives a coding agent 54 tools over the running suite. It reads the log and each function call with its error, asks the Security Rules why a request is denied, and works with your data. Nothing leaves your machine.

`npx firenook mcp add`

Sets it up for Claude Code, Cursor and VS Code in the project’s own files. Other agents run `npx firenook mcp`. [How agents use it](https://firenook.dev/mcp).

1. You

   The Stripe webhook answers 500 on my machine. Why?

2. **functions_list_calls** outcome: "failed"

   - failed

     500 stripeWebhook http POST /, 1.15 ms at 13:06:19

3. **functions_get_call** id: "e72ca3-25"

   - error

     Error: No signatures found matching the expected signature for payload

   - at

     functions/index.js:24:11

   - headers

     host, connection, content-type, accept, accept-language, sec-fetch-mode, user-agent, accept-encoding, content-length

   - body

     {"type":"checkout.session.completed"}

4. **rules_evaluate** service: "storage", method: "create", path: "products/mug.svg"

   - verdict

     deny as unauthenticated

   - line 9

     allow read, write: if false;

The question is an example. The tool calls and their answers are from a run of the demo project on firenook 0.2.0, as Firenook gave them.

- Firestore

  Read, query, count, write and delete documents

- Authentication

  Manage users, read sign-in codes, mint ID tokens, set claims

- Storage

  List, read, upload, copy, move and delete files

- Functions and logs

  Invoke a function, read each call and the log, replay a call after a fix

- Security Rules

  Ask why a request is denied, test a draft, list denials

- Pub/Sub, Tasks, Eventarc

  Publish, peek, run tasks and schedules now, replay events

## Questions

Something else? [Ask on GitHub](https://github.com/firenook-dev/firenook/issues), or read [the docs](https://firenook.dev/docs).

Do I still need firebase-tools?

Yes, for deploying and everything else the Firebase CLI does. Firenook replaces only the emulators: install it next to firebase-tools and run your emulators with it.

Does Firenook need Java?

No. Its services are native code in one npm package, with an engine for macOS, Linux and Windows, and nothing else is downloaded at install or start. Node 22, 24 or 26 runs your Functions, as it does in production.

Can I go back to the official emulator?

Yes. Firenook imports and exports the official format. While Firenook runs, export with npx firenook emulators:export ./export, then start the official emulator with --import ./export.

Which services does it emulate?

Firestore, Authentication, Cloud Storage, Cloud Functions, Extensions, Pub/Sub, Cloud Tasks and Eventarc. Realtime Database, Hosting, App Hosting and Data Connect are not emulated; a firebase.json that configures them still starts, with a warning.

Is it ready for my team?

0.2.0 is the first release for public use. Every release passes conformance replays against the official emulator and packed installs on all five platforms, and Firenook passed a two-hour benchmark against the official emulator on a real application. Commit your lockfile and upgrade on purpose.

Is it free?

Yes. Firenook is open source under the Apache License 2.0.

Is Firenook made by Google?

No. Firenook is an independent open-source project, not affiliated with or endorsed by Google. Firebase is a trademark of Google LLC.

## Switch in three steps

One package, nothing else to install: Node 22, 24 or 26 on macOS, Linux with glibc 2.28 or newer, or Windows x64. Starting a new project instead? `npx firenook init` sets one up.

1. ### Install it next to firebase-tools

   Keep firebase-tools for deploying: Firenook has no deploy or login command.

   `npm install --save-dev firenook`

2. ### Check your project

   This reads firebase.json the way the Firebase CLI does, and changes nothing.

   `npx firenook init --adopt --dry-run`

3. ### Swap the command

   Same flags and ports, so your app connects as before and your data imports as it is.

   `npx firenook emulators:start`

[Read the getting started guide](https://firenook.dev/docs/get-started/install) [Firenook on GitHub](https://github.com/firenook-dev/firenook)