write-api-docs

Write API Docs

Write clear, complete API reference documentation that developers trust and can use without guessing.

Why This Is Best Practice

Adopted by: Stripe, Twilio, GitHub, and Shopify — consistently ranked top developer-experience APIs

Impact: Stripe attributes low support volume directly to documentation quality; Twilio reports 30%+ faster onboarding for customers who read docs before integrating

Well-written API docs reduce integration time and support burden simultaneously. Developers treat docs as a contract — ambiguity breaks trust permanently. The OpenAPI Specification enforces machine-readable consistency while Stripe's style demonstrates the narrative layer on top.

Steps

1. Define the audience and use cases — identify whether readers are integrating for the first time or looking up edge cases; write for both with layered depth
2. Structure each endpoint entry — include: purpose sentence, HTTP method + path, authentication requirement, all parameters with types/constraints/defaults, request example, response schema, error codes
3. Write the purpose sentence first — one plain-language sentence explaining what the endpoint does and when to use it, before any technical detail
4. Provide runnable examples — show real request/response pairs with realistic values, not string placeholders; include curl and at least one SDK snippet
5. Document every error code — list status codes the endpoint can return, the condition that triggers each, and the recommended recovery action
6. Write an OpenAPI spec in parallel — keep narrative docs and machine-readable spec in sync; spec drives SDK generation and lint tooling
7. Add changelog entries — note deprecations, new fields, and breaking changes at the top of each affected page with version and date

Rules

• Every parameter must state: type, whether required or optional, default value, and valid range or enum values
• Never use foo, bar, or string as example values — use realistic domain data
• Breaking changes must be called out with a deprecation notice and migration path
• Code examples must be copy-paste executable without modification
• Authentication must be documented on every endpoint, not just a getting-started page

Examples

Bad: POST /charges — Creates a charge.

Good: POST /charges — Creates a new charge against a customer's payment method. Use this endpoint to collect a one-time payment; for recurring billing, use the Subscriptions API instead.

Common Mistakes

• Documenting only the happy path: developers need error states more than success states when debugging at 2 AM
• Letting examples drift from the schema: contradictions destroy trust faster than missing docs
• Burying authentication requirements: state them at the top of every endpoint, not just in an intro section

When NOT to Use

• Do not apply this skill to internal-only APIs consumed by a single team that owns both producer and consumer, where informal inline code comments and a team wiki page provide sufficient shared context without the overhead of formal reference documentation.
• Do not use this skill for GraphQL APIs where the schema is self-describing and tools like GraphiQL or Apollo Sandbox auto-generate interactive reference; applying this skill's narrative-layer approach to a self-documenting schema creates duplicate, drift-prone content.
• Do not apply this skill before the API contract is stable; writing full reference docs against an actively changing interface produces documentation debt faster than it produces value, and the effort is better spent on a draft OpenAPI spec reviewed by consumers first.