How to document REST API endpoints

Clear API documentation helps developers understand your endpoints quickly and integrate them into their systems. A good REST API guide should be easy to scan, consistent, and practical.

Why REST API documentation matters

• Reduces back-and-forth communication between developers and support teams
• Speeds up integration for internal and external consumers
• Improves reliability by clarifying required fields and explaining errors in detail

What to include for each endpoint

For every endpoint, include these core sections:

1. Endpoint summary - What the endpoint does for a user
2. Method and URL - For example, GET /api/v1/users/{id}
3. Authentication - API key, OAuth token, or no auth required
4. Request parameters:
   • Path parameters
   • Query parameters
   • Headers
5. Request body - Required and optional fields with data types
6. Response examples - Success and failure responses
7. Status codes: Meaning of codes such as 200, 400, 401, 404, 500.
8. Error model: Standard error format with sample payload.

Documenting CRUD operations

REST APIs revolve around CRUD operations. Document each operation with a clear method, endpoint path, request details, and response details.

Create (POST)

• Purpose: Create a new resource in the database.
• Method and path: POST /api/v1/users
• What to document:
  • Required and optional request body fields
  • Validation rules (format, range, uniqueness)
  • Success response (201 Created) with created resource
  • Request failures (400 Bad Request, 409 Conflict)

Read (GET)

• Purpose: Fetch one resource or a list of resources.
• Method and path:
  • Single: GET /api/v1/users/{id}
  • Collection: GET /api/v1/users
• What to document:
  • Path parameters and query parameters (page, limit, sort, filter)
  • Pagination structure (total, page, pageSize, items)
  • Success response (200 OK)
  • Not found behavior (404 Not Found)

Update (PUT or PATCH)

• Purpose: Modify existing resources.
• Method and path:
  • Full update: PUT /api/v1/users/{id}
  • Partial update: PATCH /api/v1/users/{id}
• What to document:
  • Difference between PUT (replace) and PATCH (partial change) -
  • Concurrency controls (for example ETag or version fields, if used)
  • Success response (200 OK or 204 No Content)
  • Validation and conflict errors (400, 409)

Delete (DELETE)

• Purpose: Remove or deactivate a resource.
• Method and path: DELETE /api/v1/users/{id}
• What to document:
  • Whether delete is hard delete or soft delete
  • Success response (204 No Content commonly)
  • Idempotent behavior (repeated delete request outcome)
  • Not found behavior (404 Not Found) and authorization errors (403 Forbidden)

Quick CRUD reference

Example endpoint documentation

Get user by ID

• Method: GET
• URL: /api/v1/users/{id}
• Authentication: Bearer token required

Path parameters

Request example

curl -X GET "https://api.example.com/api/v1/users/123" \
  -H "Authorization: Bearer <token>"

Success response (200)

{
  "id": "123",
  "name": "Ranjeet Kumar",
  "email": "ranjeet@example.com",
  "status": "active"
}

Error response (404)

{
  "error": {
    "code": "USER_NOT_FOUND",
    "message": "No user found with id 123"
  }
}

Child topic: Documenting POST endpoints

When documenting POST endpoints, focus on input validation, required fields, and possible creation errors.

Read the child topic for a complete walkthrough and example:

• How to document POST endpoints

Child topic: Documenting GET endpoints

When documenting GET endpoints, focus on path/query parameters, filtering, sorting, and pagination behavior.

Read the child topic for a complete walkthrough and example:

• How to document GET endpoints

Child topic: Documenting UPDATE endpoints

When documenting PUT and PATCH endpoints, clearly define replace vs partial update behavior and conflict handling.

Read the child topic for a complete walkthrough and example:

• How to document UPDATE endpoints

Child topic: Documenting DELETE endpoints

When documenting DELETE endpoints, explain hard delete vs soft delete, idempotency, and authorization rules.

Read the child topic for a complete walkthrough and example:

• How to document DELETE endpoints

Best practices for writing API docs

• Use consistent terminology and field names across all endpoints.
• Add realistic examples that developers can copy and test.
• Document validation rules (length, format, allowed values).
• Keep docs versioned with the API (v1, v2, and so on).
• Update documentation in the same pull request as code changes.

Suggested documentation workflow

1. Define a documentation template for all endpoints.
2. Write docs during development, not after release.
3. Review docs in code review for completeness.
4. Publish changelogs for breaking and non-breaking updates.