API Documentation: Writing for Developers
Good API documentation is the difference between an API that developers adopt quickly and one that causes frustration, misuse, and frequent support requests. Documentation is a product — it requires the same care as the API itself. This applies equally to internal and external APIs.
What Good API Documentation Includes
- Getting started guide: How to authenticate and make your first API call in under 5 minutes. Developers evaluate APIs by how quickly they can reach a working example.
- Reference documentation: Complete endpoint reference — URL, method, parameters, request body schema, response schema, error codes. Auto-generated from OpenAPI spec where possible.
- Code examples: Working examples in the languages your consumers use. Examples should be copy-paste runnable.
- Authentication guide: How to obtain and use credentials. Common authentication errors and how to resolve them.
- Rate limiting documentation: Limits, how they're communicated in headers, and recommended handling strategies.
- Changelog: What changed between versions — especially breaking changes and deprecation notices.
OpenAPI / Swagger
OpenAPI Specification (formerly Swagger) is the standard for describing REST APIs in a machine-readable format. An OpenAPI spec enables: auto-generated interactive documentation (Swagger UI, Redoc), client SDK generation in multiple languages, automated contract testing, and API gateway configuration. Write your spec first — it disciplines API design and provides documentation automatically.
Documentation Maintenance
Documentation that is out of sync with the actual API is worse than no documentation — it erodes trust and causes wasted debugging time. Automate documentation generation from code where possible. Include documentation updates in the definition of done for every API change.