openfeature

What this skill does

# OpenFeature SDK Integration

## When to Use This Skill

| Use this skill when... | Use a sibling skill instead when... |
|---|---|
| You need the vendor-agnostic OpenFeature SDK API, hooks, and evaluation patterns | You need the GO Feature Flag (GOFF) self-hosted backend specifics — use `go-feature-flag` |
| You are choosing between providers or wiring an OpenFeature client into application code | You want to scaffold the full feature-flag stack (SDK + provider + CI) from scratch — use `configure-feature-flags` |
| Another skill needs the canonical reference for OpenFeature semantics | You want runtime detection of an existing feature-flag setup before changing anything — use `configure-feature-flags` |

Vendor-agnostic feature flag SDK providing standardized API across languages and providers. Use when implementing feature flags, A/B testing, canary releases, or progressive rollouts with any feature flag backend.

## When to Use

**Automatic activation triggers:**
- User mentions "feature flags", "feature toggles", or "feature management"
- User asks about A/B testing or canary releases
- User wants to implement progressive rollouts
- Project has OpenFeature SDK dependencies
- User mentions OpenFeature, flagd, or vendor-agnostic flags

**Related skills:**
- `go-feature-flag` - Specific GO Feature Flag provider details
- `launchdarkly` - LaunchDarkly provider integration

## Core Concepts

### Architecture

```
┌─────────────────────────────────────────────────────────────┐
│                    Application Code                          │
├─────────────────────────────────────────────────────────────┤
│                  OpenFeature SDK (API)                       │
│  ┌─────────────┬──────────────┬─────────────┬─────────────┐ │
│  │  getBool()  │  getString() │  getNumber()│  getObject()│ │
│  └─────────────┴──────────────┴─────────────┴─────────────┘ │
├─────────────────────────────────────────────────────────────┤
│                       Provider                               │
│  ┌─────────────────────────────────────────────────────────┐ │
│  │  GO Feature Flag │ flagd │ LaunchDarkly │ Split │ etc  │ │
│  └─────────────────────────────────────────────────────────┘ │
├─────────────────────────────────────────────────────────────┤
│                    Flag Source                               │
│  ┌─────────────────────────────────────────────────────────┐ │
│  │   File   │   S3   │  GitHub  │  API  │  ConfigMap      │ │
│  └─────────────────────────────────────────────────────────┘ │
└─────────────────────────────────────────────────────────────┘
```

### Key Components

1. **API** - Standardized interface for flag evaluation
2. **Provider** - Backend-specific implementation
3. **Evaluation Context** - User/request data for targeting
4. **Hooks** - Lifecycle extensions for logging, telemetry

## SDK Installation

### Node.js (Server)

```bash
# Core SDK
npm install @openfeature/server-sdk

# Providers (choose one)
npm install @openfeature/go-feature-flag-provider  # GO Feature Flag
npm install @openfeature/flagd-provider            # flagd
npm install @openfeature/in-memory-provider        # Testing
```

### Node.js (Browser/React)

```bash
# Web SDK
npm install @openfeature/web-sdk

# React integration
npm install @openfeature/react-sdk

# Web providers
npm install @openfeature/go-feature-flag-web-provider
```

### Python

```bash
uv add openfeature-sdk
uv add openfeature-provider-go-feature-flag  # GO Feature Flag provider
```

### Go

```bash
go get github.com/open-feature/go-sdk
go get github.com/open-feature/go-sdk-contrib/providers/go-feature-flag
```

### Java

```xml
<dependency>
    <groupId>dev.openfeature</groupId>
    <artifactId>sdk</artifactId>
    <version>1.7.0</version>
</dependency>
```

### Rust

```toml
[dependencies]
open-feature = "0.2"
```

## Basic Usage Patterns

### Initialization

```typescript
// TypeScript/Node.js
import { OpenFeature } from '@openfeature/server-sdk';
import { GoFeatureFlagProvider } from '@openfeature/go-feature-flag-provider';

// Initialize provider
const provider = new GoFeatureFlagProvider({
  endpoint: process.env.GOFF_RELAY_URL || 'http://localhost:1031',
});

// Set provider (awaitable for ready state)
await OpenFeature.setProviderAndWait(provider);

// Get client
const client = OpenFeature.getClient('my-app');
```

### Flag Evaluation

```typescript
// Boolean flag
const isEnabled = await client.getBooleanValue('new-feature', false);

// String flag
const buttonColor = await client.getStringValue('button-color', '#000000');

// Number flag
const maxItems = await client.getNumberValue('max-items', 10);

// Object/JSON flag
const config = await client.getObjectValue('feature-config', {});

// With evaluation context
const context = { targetingKey: userId, email: userEmail, groups: ['beta'] };
const isEnabled = await client.getBooleanValue('new-feature', false, context);
```

### Evaluation Context

```typescript
// Creating context
const context: EvaluationContext = {
  // Required: unique identifier for targeting
  targetingKey: user.id,

  // Optional: additional attributes for targeting rules
  email: user.email,
  groups: user.roles,
  plan: user.subscription,

  // Custom attributes
  country: request.geoip.country,
  browser: request.headers['user-agent'],
};

// Set global context (applies to all evaluations)
OpenFeature.setContext(context);

// Or per-evaluation context
await client.getBooleanValue('feature', false, context);
```

### Hooks

```typescript
import { Hook, HookContext, EvaluationDetails } from '@openfeature/server-sdk';

// Logging hook
const loggingHook: Hook = {
  before: (hookContext: HookContext) => {
    console.log(`Evaluating flag: ${hookContext.flagKey}`);
  },
  after: (hookContext: HookContext, details: EvaluationDetails<unknown>) => {
    console.log(`Flag ${hookContext.flagKey} = ${details.value}`);
  },
  error: (hookContext: HookContext, error: Error) => {
    console.error(`Error evaluating ${hookContext.flagKey}:`, error);
  },
};

// Register globally
OpenFeature.addHooks(loggingHook);

// Or per-client
client.addHooks(loggingHook);
```

### React Integration

```tsx
import { OpenFeatureProvider, useFlag, useBooleanFlagValue } from '@openfeature/react-sdk';
import { GoFeatureFlagWebProvider } from '@openfeature/go-feature-flag-web-provider';

// Provider setup
const provider = new GoFeatureFlagWebProvider({
  endpoint: import.meta.env.VITE_GOFF_RELAY_URL,
});

function App() {
  return (
    <OpenFeatureProvider provider={provider}>
      <MyComponent />
    </OpenFeatureProvider>
  );
}

// Using flags in components
function MyComponent() {
  // Simple boolean value
  const isEnabled = useBooleanFlagValue('new-feature', false);

  // Full flag details
  const { value, isLoading, error } = useFlag('button-color', '#000');

  if (isLoading) return <Spinner />;

  return (
    <div>
      {isEnabled && <NewFeature />}
      <Button color={value}>Click me</Button>
    </div>
  );
}
```

## Testing

### In-Memory Provider

```typescript
import { OpenFeature } from '@openfeature/server-sdk';
import { InMemoryProvider } from '@openfeature/in-memory-provider';

// Configure test flags
const testProvider = new InMemoryProvider({
  'new-feature': {
    variants: {
      on: true,
      off: false,
    },
    defaultVariant: 'off',
    disabled: false,
  },
  'button-color': {
    variants: {
      blue: '#0066CC',
      green: '#00CC66',
    },
    defaultVariant: 'blue',
    disabled: false,
  },
});

// Use in tests
beforeAll(async () => {
  await OpenFeature.setProviderAndWait(testProvider);
});

afterAll(async () => {
  await OpenFeature.close();
});
```

### Mocking in Unit Tests

```typescript
import { vi } from 'vitest';
import { OpenFeature } from '@openfeature/server-sdk';

// Mock the entire SDK
vi.mock('@openfeature/server-sdk', () => ({
  OpenFeature: {
    getClient: vi.fn().mockReturnValue({
      getBooleanValue: vi.fn().mockResolvedValue(true),