This skill provides a complete guide for getting started with Cloud Firestore Standard Edition, including provisioning, securing, and integrating it into your application.

## Provisioning

To set up Cloud Firestore in your Firebase project and local environment, use the Firebase CLI:

```bash
npx -y firebase-tools@latest firestore:databases:create --location=<location>
```

Initialize your project for Firestore:
```bash
npx -y firebase-tools@latest init firestore
```

This generates `firestore.rules` and `firestore.indexes.json` files.

## Security Rules

Firestore Security Rules protect your data by controlling read and write access.

Basic security rules structure:

```javascript
rules_version = '2';
service cloud.firestore {
  match /databases/{database}/documents {
    match /users/{userId} {
      allow read, write: if request.auth != null && request.auth.uid == userId;
    }

    match /public/{document=**} {
      allow read: if true;
      allow write: if request.auth != null;
    }
  }
}
```

Deploy rules:
```bash
npx -y firebase-tools@latest deploy --only firestore:rules
```

## SDK Usage (Web Modular)

```typescript
import { initializeApp } from 'firebase/app';
import { getFirestore, collection, doc, getDoc, setDoc, addDoc, query, where, getDocs } from 'firebase/firestore';

const db = getFirestore(app);

// Read a document
const docRef = doc(db, 'users', userId);
const docSnap = await getDoc(docRef);
if (docSnap.exists()) {
  console.log(docSnap.data());
}

// Write a document
await setDoc(doc(db, 'users', userId), { name: 'Alice' });

// Add a document (auto-ID)
const ref = await addDoc(collection(db, 'messages'), { text: 'Hello' });

// Query documents
const q = query(collection(db, 'users'), where('age', '>=', 18));
const snapshot = await getDocs(q);
snapshot.forEach(doc => console.log(doc.data()));
```

## Indexes

Firestore requires composite indexes for queries that filter or sort on multiple fields.

- **Single-field indexes**: Created automatically for each field
- **Composite indexes**: Must be created manually for multi-field queries
- **Exemptions**: Can exclude fields from indexing to reduce storage costs

Deploy indexes:
```bash
npx -y firebase-tools@latest deploy --only firestore:indexes
```

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