firebase

Q: How do I install firebase?

Run npx skills add https://github.com/alinaqi/maggy --skill firebase in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/firebase/ (personal) or .claude/skills/firebase/ (project).

by alinaqiBackend & APIs

Firebase Firestore, Auth, Storage, real-time listeners, security rules

Installs: 299
Last 24h: —
Trending rank: —
Security: Not audited

Install

Works with every agent the skills CLI supports.

npx skills add https://github.com/alinaqi/maggy --skill firebase

01
Install
Run the command in your project. The CLI asks which agents to install for.
02
Describe the task
Ask your agent for something this skill covers. It loads firebase automatically when relevant.
03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.

SKILL.md

The instructions your agent reads when the skill is triggered.

Firebase Skill

Firebase/Firestore patterns for web and mobile applications with real-time data, offline support, and security rules.

Sources: Firebase Docs | Firestore Best Practices | Security Rules

Core Principle

Denormalize with purpose, secure with rules, scale horizontally.

Firestore is a document database - embrace denormalization for read efficiency. Security rules are your server-side validation. Design for your access patterns.

Firebase Stack

Service	Purpose
Firestore	NoSQL document database with real-time sync
Authentication	User auth, OAuth, anonymous sessions
Storage	File uploads with security rules
Functions	Serverless backend (Node.js)
Hosting	Static site + CDN
Extensions	Pre-built solutions (Stripe, Algolia, etc.)

Project Setup

Install Firebase CLI

# Install globally
npm install -g firebase-tools

# Login
firebase login

# Initialize in project
firebase init

Initialize with Emulators

firebase init emulators

# Start local development
firebase emulators:start

Project Structure

project/
├── firebase.json           # Firebase config
├── firestore.rules         # Security rules
├── firestore.indexes.json  # Composite indexes
├── storage.rules           # Storage security rules
└── functions/              # Cloud Functions
    ├── src/
    ├── package.json
    └── tsconfig.json

Firestore Data Modeling

Document Structure

// Good: Flat documents with all needed data
interface Post {
  id: string;
  title: string;
  content: string;
  authorId: string;
  authorName: string;      // Denormalized for display
  authorAvatar: string;    // Denormalized
  tags: string[];
  likeCount: number;       // Aggregated counter
  createdAt: Timestamp;
  updatedAt: Timestamp;
}

// Collection: posts/{postId}

When to Use Subcollections

// Use subcollections for:
// 1. Unbounded lists (comments, messages)
// 2. Data with different access patterns
// 3. Data that grows independently

// posts/{postId}/comments/{commentId}
interface Comment {
  id: string;
  text: string;
  authorId: string;
  authorName: string;
  createdAt: Timestamp;
}

Data Model Patterns

// Pattern 1: Embedded data (bounded, always needed)
interface User {
  id: string;
  email: string;
  profile: {
    displayName: string;
    bio: string;
    avatar: string;
  };
  settings: {
    notifications: boolean;
    theme: 'light' | 'dark';
  };
}

// Pattern 2: Reference with denormalization
interface Order {
  id: string;
  userId: string;
  userEmail: string;  // Denormalized for display
  items: OrderItem[]; // Embedded (bounded)
  total: number;
  status: 'pending' | 'paid' | 'shipped';
}

// Pattern 3: Aggregation documents
// Keep counters in parent document
interface Channel {
  id: string;
  name: string;
  memberCount: number;  // Updated via Cloud Function
  messageCount: number;
}

TypeScript SDK (Modular v9+)

Initialize Firebase

// lib/firebase.ts
import { initializeApp, getApps } from 'firebase/app';
import { getFirestore, connectFirestoreEmulator } from 'firebase/firestore';
import { getAuth, connectAuthEmulator } from 'firebase/auth';
import { getStorage, connectStorageEmulator } from 'firebase/storage';

const firebaseConfig = {
  apiKey: process.env.NEXT_PUBLIC_FIREBASE_API_KEY,
  authDomain: process.env.NEXT_PUBLIC_FIREBASE_AUTH_DOMAIN,
  projectId: process.env.NEXT_PUBLIC_FIREBASE_PROJECT_ID,
  storageBucket: process.env.NEXT_PUBLIC_FIREBASE_STORAGE_BUCKET,
  messagingSenderId: process.env.NEXT_PUBLIC_FIREBASE_MESSAGING_SENDER_ID,
  appId: process.env.NEXT_PUBLIC_FIREBASE_APP_ID
};

// Initialize only once
const app = getApps().length === 0 ? initializeApp(firebaseConfig) : getApps()[0];

export const db = getFirestore(app);
export const auth = getAuth(app);
export const storage = getStorage(app);

// Connect to emulators in development
if (process.env.NODE_ENV === 'development') {
  connectFirestoreEmulator(db, 'localhost', 8080);
  connectAuthEmulator(auth, 'http://localhost:9099');
  connectStorageEmulator(storage, 'localhost', 9199);
}

CRUD Operations

import {
  collection,
  doc,
  getDoc,
  getDocs,
  addDoc,
  setDoc,
  updateDoc,
  deleteDoc,
  query,
  where,
  orderBy,
  limit,
  startAfter,
  serverTimestamp,
  Timestamp
} from 'firebase/firestore';
import { db } from './firebase';

// Create
async function createPost(data: Omit<Post, 'id' | 'createdAt' | 'updatedAt'>) {
  const docRef = await addDoc(collection(db, 'posts'), {
    ...data,
    createdAt: serverTimestamp(),
    updatedAt: serverTimestamp()
  });
  return docRef.id;
}

// Read single document
async function getPost(postId: string): Promise<Post | null> {
  const docSnap = await getDoc(doc(db, 'posts', postId));
  if (!docSnap.exists()) return null;
  return { id: docSnap.id, ...docSnap.data() } as Post;
}

// Query with filters
async function getPostsByAuthor(authorId: string, pageSize = 10) {
  const q = query(
    collection(db, 'posts'),
    where('authorId', '==', authorId),
    orderBy('createdAt', 'desc'),
    limit(pageSize)
  );
  const snapshot = await getDocs(q);
  return snapshot.docs.map(doc => ({ id: doc.id, ...doc.data() } as Post));
}

// Pagination
async function getNextPage(lastDoc: Post, pageSize = 10) {
  const q = query(
    collection(db, 'posts'),
    orderBy('createdAt', 'desc'),
    startAfter(lastDoc.createdAt),
    limit(pageSize)
  );
  const snapshot = await getDocs(q);
  return snapshot.docs.map(doc => ({ id: doc.id, ...doc.data() } as Post));
}

// Update
async function updatePost(postId: string, data: Partial<Post>) {
  await updateDoc(doc(db, 'posts', postId), {
    ...data,
    updatedAt: serverTimestamp()
  });
}

// Delete
async function deletePost(postId: string) {
  await deleteDoc(doc(db, 'posts', postId));
}

Real-time Listeners

import { onSnapshot, QuerySnapshot, DocumentSnapshot } from 'firebase/firestore';

// Listen to single document
function subscribeToPost(
  postId: string,
  onData: (post: Post | null) => void,
  onError: (error: Error) => void
) {
  return onSnapshot(
    doc(db, 'posts', postId),
    (snapshot: DocumentSnapshot) => {
      if (!snapshot.exists()) {
        onData(null);
        return;
      }
      onData({ id: snapshot.id, ...snapshot.data() } as Post);
    },
    onError
  );
}

// Listen to collection with query
function subscribeToPosts(
  authorId: string,
  onData: (posts: Post[]) => void,
  onError: (error: Error) => void
) {
  const q = query(
    collection(db, 'posts'),
    where('authorId', '==', authorId),
    orderBy('createdAt', 'desc')
  );

  return onSnapshot(
    q,
    (snapshot: QuerySnapshot) => {
      const posts = snapshot.docs.map(doc => ({
        id: doc.id,
        ...doc.data()
      } as Post));
      onData(posts);
    },
    onError
  );
}

// React hook example
function usePost(postId: string) {
  const [post, setPost] = useState<Post | null>(null);
  const [loading, setLoading] = useState(true);
  const [error, setError] = useState<Error | null>(null);

  useEffect(() => {
    const unsubscribe = subscribeToPost(
      postId,
      (data) => {
        setPost(data);
        setLoading(false);
      },
      (err) => {
        setError(err);
        setLoading(false);
      }
    );
    return unsubscribe;
  }, [postId]);

  return { post, loading, error };
}

Offline Persistence (Web)

import { enableIndexedDbPersistence, enableMultiTabIndexedDbPersistence } from 'firebase/firestore';

// Enable offline persistence (call once at startup)
async function enableOffline() {
  try {
    // Single tab
    await enableIndexedDbPersistence(db);

    // OR multi-tab (recommended)
    await enableMultiTabIndexedDbPersistence(db);
  } catch (err: any) {
    if (err.code === 'failed-precondition') {
      // Multiple tabs open, only works in one
      console.warn('Persistence only available in one tab');
    } else if (err.code === 'unimplemented') {
      // Browser doesn't support
      console.warn('Persistence not supported');
    }
  }
}

// Check if data is from cache
onSnapshot(docRef, (snapshot) => {
  const source = snapshot.metadata.fromCache ? 'cache' : 'server';
  console.log(`Data from ${source}`);

  if (snapshot.metadata.hasPendingWrites) {
    console.log('Local changes pending sync');
  }
});

Security Rules

Basic Rules Structure

// firestore.rules
rules_version = '2';
service cloud.firestore {
  match /databases/{database}/documents {

    // Helper functions
    function isAuthenticated() {
      return request.auth != null;
    }

    function isOwner(userId) {
      return request.auth.uid == userId;
    }

    function isAdmin() {
      return request.auth.token.admin == true;
    }

    // Posts collection
    match /posts/{postId} {
      // Anyone can read published posts
      allow read: if resource.data.status == 'published';

      // Only authenticated users can create
      allow create: if isAuthenticated()
        && request.resource.data.authorId == request.auth.uid
        && request.resource.data.keys().hasAll(['title', 'content', 'authorId']);

      // Only author can update
      allow update: if isOwner(resource.data.authorId)
        && request.resource.data.authorId == resource.data.authorId; // Can't change author

      // Only author or admin can delete
      allow delete: if isOwner(resource.data.authorId) || isAdmin();

      // Comments subcollection
      match /comments/{commentId} {
        allow read: if true;
        allow create: if isAuthenticated();
        allow update, delete: if isOwner(resource.data.authorId);
      }
    }

    // User profiles
    match /users/{userId} {
      allow read: if true;
      allow create: if isAuthenticated() && isOwner(userId);
      allow update: if isOwner(userId);
      allow delete: if false; // Never allow delete
    }

    // Private user data
    match /users/{userId}/private/{document=**} {
      allow read, write: if isOwner(userId);
    }
  }
}

Data Validation in Rules

match /posts/{postId} {
  function isValidPost() {
    let data = request.resource.data;
    return data.title is string
      && data.title.size() >= 3
      && data.title.size() <= 100
      && data.content is string
      && data.content.size() <= 50000
      && data.tags is list
      && data.tags.size() <= 5;
  }

  allow create: if isAuthenticated() && isValidPost();
  allow update: if isOwner(resource.data.authorId) && isValidPost();
}

Test Rules Locally

# Install emulators
firebase emulators:start

# Run rules tests
npm test

// tests/firestore.rules.test.ts
import { assertFails, assertSucceeds, initializeTestEnvironment } from '@firebase/rules-unit-testing';

describe('Firestore Rules', () => {
  let testEnv: RulesTestEnvironment;

  beforeAll(async () => {
    testEnv = await initializeTestEnvironment({
      projectId: 'test-project',
      firestore: { rules: fs.readFileSync('firestore.rules', 'utf8') }
    });
  });

  test('unauthenticated users cannot write', async () => {
    const unauthedDb = testEnv.unauthenticatedContext().firestore();
    await assertFails(
      setDoc(doc(unauthedDb, 'posts/test'), { title: 'Test' })
    );
  });

  test('users can only update own posts', async () => {
    const aliceDb = testEnv.authenticatedContext('alice').firestore();
    const bobDb = testEnv.authenticatedContext('bob').firestore();

    // Create as Alice
    await assertSucceeds(
      setDoc(doc(aliceDb, 'posts/test'), { title: 'Test', authorId: 'alice' })
    );

    // Bob cannot update
    await assertFails(
      updateDoc(doc(bobDb, 'posts/test'), { title: 'Hacked' })
    );
  });
});

Authentication

Email/Password Auth

import {
  createUserWithEmailAndPassword,
  signInWithEmailAndPassword,
  signOut,
  onAuthStateChanged,
  User
} from 'firebase/auth';
import { auth } from './firebase';

// Sign up
async function signUp(email: string, password: string) {
  const credential = await createUserWithEmailAndPassword(auth, email, password);
  return credential.user;
}

// Sign in
async function signIn(email: string, password: string) {
  const credential = await signInWithEmailAndPassword(auth, email, password);
  return credential.user;
}

// Sign out
async function logout() {
  await signOut(auth);
}

// Auth state listener
function onAuthChange(callback: (user: User | null) => void) {
  return onAuthStateChanged(auth, callback);
}

OAuth Providers

import {
  GoogleAuthProvider,
  signInWithPopup,
  signInWithRedirect
} from 'firebase/auth';

const googleProvider = new GoogleAuthProvider();

async function signInWithGoogle() {
  try {
    const result = await signInWithPopup(auth, googleProvider);
    return result.user;
  } catch (error) {
    // Handle errors
    throw error;
  }
}

Cloud Functions

Basic HTTP Function

// functions/src/index.ts
import { onRequest } from 'firebase-functions/v2/https';
import { onDocumentCreated } from 'firebase-functions/v2/firestore';
import { initializeApp } from 'firebase-admin/app';
import { getFirestore } from 'firebase-admin/firestore';

initializeApp();
const db = getFirestore();

// HTTP endpoint
export const helloWorld = onRequest((request, response) => {
  response.json({ message: 'Hello from Firebase!' });
});

// Firestore trigger
export const onPostCreated = onDocumentCreated('posts/{postId}', async (event) => {
  const snapshot = event.data;
  if (!snapshot) return;

  const post = snapshot.data();

  // Update author's post count
  await db.doc(`users/${post.authorId}`).update({
    postCount: FieldValue.increment(1)
  });
});

Callable Functions

// Backend
import { onCall, HttpsError } from 'firebase-functions/v2/https';

export const createPost = onCall(async (request) => {
  // Auth check
  if (!request.auth) {
    throw new HttpsError('unauthenticated', 'Must be logged in');
  }

  const { title, content } = request.data;

  // Validation
  if (!title || title.length < 3) {
    throw new HttpsError('invalid-argument', 'Title must be at least 3 characters');
  }

  // Create post
  const postRef = await db.collection('posts').add({
    title,
    content,
    authorId: request.auth.uid,
    createdAt: FieldValue.serverTimestamp()
  });

  return { postId: postRef.id };
});

// Frontend
import { getFunctions, httpsCallable } from 'firebase/functions';

const functions = getFunctions();
const createPostFn = httpsCallable(functions, 'createPost');

async function createPost(title: string, content: string) {
  const result = await createPostFn({ title, content });
  return result.data as { postId: string };
}

Batch Operations & Transactions

Batch Writes

import { writeBatch, doc } from 'firebase/firestore';

async function batchUpdate(updates: { id: string; data: any }[]) {
  const batch = writeBatch(db);

  updates.forEach(({ id, data }) => {
    batch.update(doc(db, 'posts', id), data);
  });

  await batch.commit(); // Atomic
}

Transactions

import { runTransaction, doc, increment } from 'firebase/firestore';

async function likePost(postId: string, userId: string) {
  await runTransaction(db, async (transaction) => {
    const postRef = doc(db, 'posts', postId);
    const likeRef = doc(db, 'posts', postId, 'likes', userId);

    const postSnap = await transaction.get(postRef);
    if (!postSnap.exists()) throw new Error('Post not found');

    const likeSnap = await transaction.get(likeRef);
    if (likeSnap.exists()) throw new Error('Already liked');

    transaction.set(likeRef, { createdAt: serverTimestamp() });
    transaction.update(postRef, { likeCount: increment(1) });
  });
}

Indexes

Composite Indexes

// firestore.indexes.json
{
  "indexes": [
    {
      "collectionGroup": "posts",
      "queryScope": "COLLECTION",
      "fields": [
        { "fieldPath": "authorId", "order": "ASCENDING" },
        { "fieldPath": "createdAt", "order": "DESCENDING" }
      ]
    },
    {
      "collectionGroup": "posts",
      "queryScope": "COLLECTION",
      "fields": [
        { "fieldPath": "tags", "arrayConfig": "CONTAINS" },
        { "fieldPath": "createdAt", "order": "DESCENDING" }
      ]
    }
  ]
}

# Deploy indexes
firebase deploy --only firestore:indexes

CLI Quick Reference

# Project setup
firebase login                       # Authenticate
firebase init                        # Initialize project
firebase projects:list               # List projects

# Emulators
firebase emulators:start             # Start all emulators
firebase emulators:start --only firestore,auth  # Specific emulators

# Deploy
firebase deploy                      # Deploy everything
firebase deploy --only firestore     # Deploy rules + indexes
firebase deploy --only functions     # Deploy functions
firebase deploy --only hosting       # Deploy hosting

# Functions
cd functions && npm run build        # Build TypeScript
firebase functions:log               # View logs

Anti-Patterns

No security rules - Always write rules, never use test mode in production
Deep nesting - Keep documents flat, max 2-3 levels
Large documents - Max 1MB, split if larger
Unbounded arrays - Use subcollections for lists that grow
No offline handling - Enable persistence for mobile/PWA
Reading all fields - Use field masks or Firestore Lite
Ignoring indexes - Check console for missing index errors
No emulator testing - Always test rules before deploy

FAQ

What does the firebase skill do?

Firebase Firestore, Auth, Storage, real-time listeners, security rules

How do I install firebase?

Run npx skills add https://github.com/alinaqi/maggy --skill firebase in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/firebase/ (personal) or .claude/skills/firebase/ (project).

Which AI agents can use firebase?

Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.

Is firebase safe to install?

No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.

Who maintains firebase?

It is published by alinaqi in alinaqi/maggy. It has 299 recorded installs.

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firebase

Install

Install

Describe the task

Review the result

SKILL.md

Firebase Skill

Core Principle

Firebase Stack

Project Setup

Install Firebase CLI

Initialize with Emulators

Project Structure

Firestore Data Modeling

Document Structure

When to Use Subcollections

Data Model Patterns

TypeScript SDK (Modular v9+)

Initialize Firebase

CRUD Operations

Real-time Listeners

Offline Persistence (Web)

Security Rules

Basic Rules Structure

Data Validation in Rules

Test Rules Locally

Authentication

Email/Password Auth

OAuth Providers

Cloud Functions

Basic HTTP Function

Callable Functions

Batch Operations & Transactions

Batch Writes

Transactions

Indexes

Composite Indexes

CLI Quick Reference

Anti-Patterns

FAQ

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