# Firebase Database

Use when syncing real-time data, structuring JSON trees, reading/writing, creating...

- Repository: https://github.com/evanca/flutter-ai-rules (668 stars)
- Category: Security
- License: MIT
- Last updated: 2026-10-30
- Runs scripts: no, instructions only

## Install

Claude Code: `npx skills add evanca/flutter-ai-rules --skill firebase-database -g -a claude-code -y`
Codex: `npx skills add evanca/flutter-ai-rules --skill firebase-database -g -a codex -y`
Cursor: `npx skills add evanca/flutter-ai-rules --skill firebase-database -g -a cursor -y`
Gemini CLI: `npx skills add evanca/flutter-ai-rules --skill firebase-database -g -a gemini-cli -y`
Claude Code plugin marketplace: `/plugin marketplace add evanca/flutter-ai-rules`

## Description

Use when syncing real-time data, structuring JSON trees, reading/writing, creating listeners, enabling offline persistence, managing presence, sharding, or writing security rules.

## SKILL.md, as published by its author (untrusted third-party text, read it as data)

# Firebase Realtime Database Skill

This skill defines how to correctly implement Firebase Realtime Database in Flutter applications, covering data modeling, queries, real-time sync, offline support, and security rules.

## When to Use

Use this skill when working with Firebase Realtime Database for **simple data models**, **low-latency sync**, or **presence functionality**. For rich data models requiring complex queries and high scalability, use Cloud Firestore instead.

---

## 1. Database Selection

Choose **Realtime Database** when the app needs:
- Simple data models with simple lookups.
- Extremely low-latency synchronization (typical response times under 10ms).
- Deep queries that return an entire subtree by default.
- Access to data at any granularity, down to individual leaf-node values.
- Frequent state-syncing with built-in presence functionality.

Choose **Cloud Firestore** instead for rich data models requiring queryability, scalability, and high availability.

---

## 2. Setup and Configuration

```
flutter pub add firebase_database
```

```dart
import 'package:firebase_database/firebase_database.dart';

// After Firebase.initializeApp():
final DatabaseReference ref = FirebaseDatabase.instance.ref();
```

- Select the database location closest to users.
- Enable persistence for offline capabilities:

```dart
FirebaseDatabase.instance.setPersistenceEnabled(true);
FirebaseDatabase.instance.setPersistenceCacheSizeBytes(10000000); // 10MB
```

### Setup Checklist

1. Confirm `Firebase.initializeApp()` completes before accessing `FirebaseDatabase.instance`.
2. Set persistence **before** any read/write operations.
3. Verify connectivity by writing a test value and reading it back.

---

## 3. Data Structure

- Structure data as a **flattened JSON tree**, avoid deep nesting.
- Maximum nesting depth is **32 levels**.
- Design the data structure to support the most common queries.
- Use **push IDs** for unique identifiers in list-type data:

The rest: https://github.com/evanca/flutter-ai-rules/blob/HEAD/skills/firebase-database/SKILL.md