Firebase Mocker

A TypeScript-based emulator of the Firebase services. It provides separate servers. The Firebase Admin SDK connects to these local servers when the corresponding emulator environment variables are set.

• Firestore (gRPC)
• Firebase Auth (HTTP)

Overview

Firebase Mocker can run:

1. Firestore emulator — A gRPC server that implements the Firestore service contract. The Admin SDK talks to it when FIRESTORE_EMULATOR_HOST is set. Use it for local development, integration tests, and CI without real Firestore credentials.

2. Firebase Auth emulator — An HTTP server that implements the Identity Toolkit REST API. The Admin SDK Auth API (e.g. getUserByEmail, createUser, deleteUser) uses it when FIREBASE_AUTH_EMULATOR_HOST is set. Use it to test auth flows without hitting production Firebase Auth.

You can start one or both servers in the same process (e.g. in your test setup). Each server is independent: start only what your tests or app need.

Installation

Install as a devDependency in your project (recommended for tests and local development):

npm install -D firebase-mocker

Or add to your project's package.json:

{
  "devDependencies": {
    "firebase-mocker": "^1.0.0"
  }
}

Then run npm install.

Development setup

npm install
npm run build

Configuration

Configuration is passed when starting each server. You can pass different options to startFirestoreServer() and startAuthServer().

Firestore server options

When calling startFirestoreServer(config):

• port — gRPC server port (default 3333)
• host — Bind address (e.g. 'localhost', or '0.0.0.0' for all interfaces)
• projectId — Project ID (must match the one used in your Firebase Admin app)

Firebase Auth server options

When calling startAuthServer(config):

• port — HTTP server port (default 9099)
• host — Bind address (default 'localhost')
• projectId — Project ID (optional)

Common options

For logs, use addConfig({ logs: { ... } }) before starting servers:

• verboseGrpcLogs — Log every gRPC call (default false). Set true for debugging.
• verboseAuthLogs — Log Auth API requests (default false).
• onUnimplemented — When an RPC is not implemented: 'warn' (default) writes a clear message to stderr and returns UNIMPLEMENTED; 'throw' throws so the process fails. Example: addConfig({ logs: { onUnimplemented: 'throw' } }) for strict CI.

Usage

Start only the servers you need. Each method sets the corresponding environment variable so the Firebase Admin SDK uses that emulator.

1. Firestore server only

Start the Firestore gRPC emulator. The Admin SDK will use it for admin.firestore() when FIRESTORE_EMULATOR_HOST is set (done automatically by startFirestoreServer()).

import { firebaseMocker } from 'firebase-mocker';
import * as admin from 'firebase-admin';

// Start the Firestore emulator (sets FIRESTORE_EMULATOR_HOST)
const firestoreServer = await firebaseMocker.startFirestoreServer({
  port: 3333,
  host: 'localhost',
  projectId: 'my-project',
});

// Initialize Firebase Admin — it will use the emulator
admin.initializeApp({ projectId: 'my-project' });
const db = admin.firestore();

// Use Firestore as usual; all calls go to the emulator via gRPC
const ref = db.collection('users').doc('user1');
await ref.set({ name: 'Jane', email: 'jane@example.com' });
const snap = await ref.get();
console.log(snap.data());

// When done (e.g. after tests)
await firebaseMocker.stopFirestoreServer();

• Before initializing the Admin SDK, call startFirestoreServer() so FIRESTORE_EMULATOR_HOST is set.
• Use the returned FirestoreServer for getStorage() (test helpers); use firebaseMocker.stopFirestoreServer() to shut down.

2. Firebase Auth server only

Start the Auth HTTP emulator. The Admin SDK will use it for admin.auth() when FIREBASE_AUTH_EMULATOR_HOST is set (done automatically by startAuthServer()).

import { firebaseMocker } from 'firebase-mocker';
import * as admin from 'firebase-admin';

// Start the Auth emulator (sets FIREBASE_AUTH_EMULATOR_HOST)
const authServer = await firebaseMocker.startAuthServer({
  port: 9099,
  host: 'localhost',
  projectId: 'my-project',
});

// Initialize Firebase Admin — Auth API will use the emulator
admin.initializeApp({ projectId: 'my-project' });
const auth = admin.auth();

// Use Auth as usual (createUser, getUserByEmail, deleteUser, etc.)
const user = await auth.createUser({ email: 'jane@example.com', password: 'secret' });
console.log(user.uid);

// When done
await firebaseMocker.stopAuthServer();

• Before initializing the Admin SDK, call startAuthServer() so FIREBASE_AUTH_EMULATOR_HOST is set.
• Use authServer.getStorage() to access the in-memory user store (e.g. to assert created users in tests).
• Use firebaseMocker.stopAuthServer() to stop the server (the package keeps a reference to the last started Auth server).

3. Both servers (Firestore + Auth)

You can run both emulators in the same process (e.g. in test setup). Start both before initializing the Admin SDK.

import { firebaseMocker } from 'firebase-mocker';
import * as admin from 'firebase-admin';

// Start both emulators; pass each server its options (stored under "firestore" and "firebase-auth" internally)
const firestoreServer = await firebaseMocker.startFirestoreServer({
  port: 3333,
  host: 'localhost',
  projectId: 'my-project',
});
const authServer = await firebaseMocker.startAuthServer({
  port: 9099,
  host: 'localhost',
  projectId: 'my-project',
});

// Now both admin.firestore() and admin.auth() use the emulators
admin.initializeApp({ projectId: 'my-project' });
const db = admin.firestore();
const auth = admin.auth();

// ... use db and auth ...

// Teardown: stop both via firebaseMocker
await firebaseMocker.stopFirestoreServer();
await firebaseMocker.stopAuthServer();

Implemented APIs

Firestore (gRPC)

The Firestore emulator implements these gRPC methods:

Method	Supported	Used by Firebase Admin SDK for
GetDocument	Yes	Single document fetch (doc(id).get())
ListDocuments	Yes	List documents in a collection
RunQuery	Yes	Queries (collection.get(), where(), orderBy())
RunAggregationQuery	Yes	Aggregation queries, e.g. count().get() (COUNT supported; sum/avg return 0)
CreateDocument	Yes	Create document with server-generated ID
UpdateDocument	Yes	Update existing document
DeleteDocument	Yes	Delete document
Commit	Yes	Writes: set(), add(), update(), delete()
BatchGetDocuments	Yes	Batched reads, e.g. doc(id).get()
Listen	Yes	Real-time listeners (streaming)
Write	Yes	Write stream (used by client SDK)
ListCollectionIds	Yes	List subcollection IDs under a document (doc.ref.listCollections())
BatchWrite	No	Returns UNIMPLEMENTED; see onUnimplemented in Configuration
BeginTransaction	No	Returns UNIMPLEMENTED
Rollback	No	Returns UNIMPLEMENTED

When an unsupported RPC is called, the emulator logs a clear warning to stderr (or throws if logs.onUnimplemented is 'throw'). See Configuration for onUnimplemented.

RunQuery: order, limit, pagination and related behaviour

Within RunQuery (queries like collection.where(...).orderBy(...).limit(n).get()), the following are implemented or not:

Feature	Implemented	Notes
orderBy	Yes	Multiple sort fields, ASC/DESC; supports __name__ (document ID).
limit	Yes	Max number of documents; supports numeric and protobuf { value: n } form.
offset	Yes	Number of documents to skip before returning results.
where (field filter)	Yes	Single-field conditions (EQUAL, LESS_THAN, etc.).
where (composite filter)	Yes	AND/OR of multiple filters.
where (unary filter)	Yes	IS_NULL, IS_NAN, etc.
start_at / startAt (Cursor)	No	Cursor-based “start at” (SDK: startAt() / startAfter()). Not applied; all matching docs are considered from the beginning.
end_at / endAt (Cursor)	No	Cursor-based “end at” (SDK: endAt() / endBefore()). Not applied; results are not trimmed by cursor.

So offset + limit pagination works; cursor-based pagination (start_at/end_at) is not implemented.

Firebase Auth (HTTP)

The Auth emulator exposes the Identity Toolkit REST API under /identitytoolkit.googleapis.com/v1/projects/:projectId/.... The Firebase Admin SDK uses it when FIREBASE_AUTH_EMULATOR_HOST is set. The server stores users in memory; use the returned AuthServer.getStorage() for test helpers.

API endpoint	Supported	Used by Firebase Admin SDK for
accounts:lookup	Yes	getUser(uid), getUserByEmail(email), getUserByPhoneNumber(phone)
accounts (POST)	Yes	createUser({ email, password, ... })
accounts:delete	Yes	deleteUser(uid)
accounts:update	Yes	updateUser(uid, { ... })
Other Identity Toolkit endpoints	No	Return 404 (e.g. custom token sign-in, email link, etc.)

Technical notes

• Firestore protocol: gRPC only. The Firestore server uses the same proto definitions as the official client (@google-cloud/firestore). No REST API for Firestore.
• Auth protocol: HTTP (REST). The Auth server implements the Identity Toolkit API that the Firebase Admin Auth client calls when FIREBASE_AUTH_EMULATOR_HOST is set.
• IPv6 (Firestore): The Firestore server binds to [::]:port so it accepts both IPv4 and IPv6 (Firebase Admin SDK may use IPv6).
• Proto source: The server loads definitions from proto/v1.json (bundled in this package). That file is a copy of @google-cloud/firestore/build/protos/v1.json. To update it (e.g. after upgrading firebase-admin), run: cp node_modules/@google-cloud/firestore/build/protos/v1.json proto/v1.json from the firebase-mocker package root.
• Implementation alignment: When adding or changing RPCs, compare with the definitions in @google-cloud/firestore/build/protos/.
• Field naming: Response messages use a mix of snake_case and camelCase depending on the RPC (CommitResponse/WriteResult use snake_case; BatchGetDocumentsResponse/Document use camelCase). Do not change them without testing both document creation and reads.
• Null values: In gRPC Value messages, null must be encoded as nullValue: 0, not nullValue: null, or the Firebase Admin SDK may throw when decoding.

Status

Firestore emulator — Implemented and in use:

• Basic CRUD (get, set, update, delete) via Commit, GetDocument, BatchGetDocuments, CreateDocument, UpdateDocument, DeleteDocument
• Queries with filters, orderBy, limit, offset (RunQuery); composite and unary filters supported
• Batch get (doc(id).get())
• Real-time listeners (Listen) and Write stream
• Aggregation queries (RunAggregationQuery; COUNT supported)
• ListCollectionIds (doc.ref.listCollections())

Firebase Auth emulator — Implemented: lookup, createUser, deleteUser, updateUser (Identity Toolkit API in memory).

Possible future work:

• Transactions (BeginTransaction, Rollback), BatchWrite
• Cursor-based pagination (startAt/endAt) in RunQuery
• Persistence to disk
• Security rules emulation

License

MIT