# Specification: REST API

**ID**: SPEC-203
**Version**: 1.0
**Date**: 2025-10-24
**Status**: Active
**Author**: API Team

## Overview

This specification defines the RESTful API endpoints, request/response formats, and error handling for the application.

## Background

The application exposes a REST API for client applications to interact with backend services.

## Requirements

### Endpoint Design

**REQ-001**: The system shall follow REST principles for all API endpoints.

**REQ-002**: The system shall version API endpoints using the URL path (e.g., `/api/v1/users`).

**REQ-003**: The system shall return appropriate HTTP status codes for all responses.

### Authentication

**REQ-004**: The system shall require a valid session token in the Authorization header for protected endpoints. [Related to SPEC-200/REQ-009]

**REQ-005**: IF a request to a protected endpoint lacks a valid token, THEN the system shall return HTTP 401 Unauthorized.

### Request Handling

**REQ-006**: The system shall accept JSON request bodies for POST, PUT, and PATCH operations.

**REQ-007**: WHEN a request contains invalid JSON, the system shall return HTTP 400 Bad Request with a descriptive error message.

### Response Format

**REQ-008**: The system shall return JSON responses for all endpoints.

**REQ-009**: The system shall include a `data` field containing the response payload in successful responses.

**REQ-010**: The system shall include an `error` field containing error details in error responses.

### Performance

**NFR-001**: The system shall respond to API requests within 200 milliseconds for the 95th percentile.

**NFR-002**: The system shall support at least 1000 requests per second per instance.

### Error Handling

**REQ-011**: The system shall return structured error responses with error codes and messages.

**REQ-012**: The system shall log all error responses for debugging purposes.

## API Conventions

### Response Format
```json
{
  "data": {...},
  "meta": {
    "timestamp": "2025-10-24T12:00:00Z",
    "version": "v1"
  }
}
```

### Error Format
```json
{
  "error": {
    "code": "INVALID_INPUT",
    "message": "Email address is required",
    "field": "email"
  }
}
```

## Related Specifications

- SPEC-200: User Authentication System
- SPEC-204: Database Schema

## Revision History

- 2025-10-24: Initial version
