> ## Documentation Index
> Fetch the complete documentation index at: https://docs.solute.so/llms.txt
> Use this file to discover all available pages before exploring further.

# Backend API Introduction

> Overview of the Solute SDK backend API

## Backend API

The Solute SDK requires a backend API to receive events and serve feature flags. This section documents the API endpoints that your backend must implement.

## Base URL

```
https://api.solute.dev
```

## Authentication

All requests must include the API key in the `X-Api-Key` header:

```
X-Api-Key: your_api_key_here
```

## Required Endpoints

Your backend must implement at least these two endpoints:

* **POST /api/events** - Receive batched events from the SDK
* **GET /api/feature-flags** - Serve feature flags for a user

## Optional Endpoints

These endpoints are optional but recommended:

* **POST /api/identify** - Update user traits (can also be sent via `/api/events`)
* **POST /api/group** - Associate users with groups
* **POST /api/alias** - Merge user identities

## Rate Limiting

Recommended rate limits:

* Event ingestion: 1000 requests/minute per API key
* Feature flags: 100 requests/minute per API key
* Identify/Group/Alias: 500 requests/minute per API key

Return `429 Too Many Requests` when limits are exceeded.

## Error Responses

All endpoints should return errors in this format:

```json theme={null}
{
  "error": {
    "code": "INVALID_API_KEY",
    "message": "Invalid or missing API key",
    "details": {}
  },
  "statusCode": 401
}
```

### Common Error Codes

* `INVALID_API_KEY` - Invalid or missing API key
* `VALIDATION_ERROR` - Request body validation failed
* `RATE_LIMIT_EXCEEDED` - Too many requests
* `INTERNAL_ERROR` - Server error
* `NOT_FOUND` - Resource not found

## Next Steps

<CardGroup cols={2}>
  <Card title="Authentication" icon="key" href="/backend-api/authentication" />

  <Card title="Events Endpoint" icon="chart-line" href="/backend-api/events" />

  <Card title="Feature Flags Endpoint" icon="flask" href="/backend-api/feature-flags" />
</CardGroup>