API PRD Template for Developer Products

An API PRD template must include developer personas, endpoint contracts, authentication flows, versioning strategy, rate limits, error codes, and SLA commitments. Generic PRD templates omit every one of these sections. The template below is structured for REST APIs; adapt section 3 for GraphQL or gRPC as needed.

Why API PRDs need their own template

A developer product has a different primary persona (a developer, not an end user), a different success metric (integration success rate, time-to-first-successful-call), and a different failure mode (a breaking change that silently corrupts downstream integrations). None of these appear in a standard consumer-product PRD template.

The most expensive API failure is an undocumented breaking change. The second most expensive is an auth flow that takes longer than 30 minutes to complete. Both are preventable with a PRD that asks the right questions before a single endpoint is designed.

The API PRD template

1. Developer persona

Primary: Backend engineer at a SaaS company integrating [your product] into their existing workflow. Comfortable with REST APIs, OAuth 2.0, and JSON. Expects OpenAPI spec and a working Postman collection. Does not want to read prose documentation to understand what an endpoint does.

Secondary: Solo developer / indie hacker building a side project. May be less familiar with enterprise auth flows. Needs a quick-start guide that produces a working API call in under 10 minutes.

2. Objective

Example: Launch a REST API for [resource] that enables developers to [primary action] and [secondary action], with a target of under 10 minutes from API key creation to first successful authenticated request.

3. Endpoint contracts

For each endpoint, specify: method, path, authentication required, request body schema, response schema, and error responses. Do not leave schemas to engineering to define, define them in the PRD.

POST /v1/prds

Auth: Bearer token (API key). Rate limit: 100 requests/min per API key.

Request body: {"input": "string (required, max 10,000 chars)", "format": "markdown | json (optional, default: json)"}

Response 201: {"id": "string", "status": "generating | complete", "prd": {...} | null, "created_at": "ISO 8601"}

Response 400: Invalid input, {"error": "invalid_input", "message": "input exceeds 10,000 character limit"}

Response 429: Rate limit exceeded, {"error": "rate_limit_exceeded", "retry_after": 60}

4. Authentication flow

Auth method: API key (Bearer token in Authorization header). OAuth 2.0 for workspace-level access (v2, out of scope for this release).

Key creation: Self-serve via dashboard. Instant provisioning. No approval flow for standard tier.

Key scopes: read (GET endpoints), write (POST/PATCH/DELETE), admin (key management). Keys created with write scope by default.

Key rotation: User-initiated. Old key active for 24-hour grace period after rotation. Webhook notification on key rotation.

Time to first successful call target: Under 10 minutes from account creation to authenticated API response.

5. Versioning strategy

Version in URL path: /v1/ prefix. New major versions on breaking changes only.

Deprecation policy: Minimum 12-month deprecation window for any v1 endpoint. Email notification to all active API key holders 90 days before deprecation. Migration guide published at deprecation announcement.

What constitutes a breaking change: Removing an endpoint, removing a required or optional response field, changing a field's data type, changing an error code's meaning. Additive changes (new optional fields, new endpoints) are non-breaking and do not require a version bump.

6. Rate limits

Tier	Requests / minute	Requests / day	Response on exceed
Free	10	100	429 + Retry-After header
Pro	100	5,000	429 + Retry-After header
Enterprise	Custom	Custom	429 + Retry-After header

Rate limit headers returned on every response: X-RateLimit-Limit, X-RateLimit-Remaining, X-RateLimit-Reset (Unix timestamp).

7. Error codes

Document every error code before engineering builds. Undocumented error codes are the leading cause of API support tickets.

HTTP status	Error code	Meaning	Developer action
400	invalid_input	Request body fails validation	Check message field for specific validation error
401	unauthorized	Missing or invalid API key	Check Authorization header format: Bearer [key]
403	insufficient_scope	API key lacks required scope	Create a new key with write scope
404	not_found	Resource does not exist	Verify the resource ID in the path
429	rate_limit_exceeded	Rate limit hit	Wait retry_after seconds and retry
500	internal_error	Unexpected server error	Retry with exponential backoff; contact support if persistent
503	service_unavailable	Planned maintenance or capacity	Check status page; retry after Retry-After header value

8. SLA commitments

Uptime SLA: 99.9% monthly (Pro and Enterprise). Calculated as: (total minutes − downtime minutes) / total minutes.

Latency SLA: p95 response time under 500ms for synchronous endpoints. Async generation endpoints excluded from latency SLA; status polling endpoint (GET /v1/prds/{id}) included.

Status page: status.scriptonia.dev. Webhooks available for incident notifications.

9. Developer experience requirements

OpenAPI 3.1 spec published at /openapi.json and /openapi.yaml before launch.

Postman collection with pre-configured auth and example requests for all endpoints.

Quick-start guide: 5 steps, working code example in JavaScript and Python, reaches first successful API call in under 10 minutes for a developer reading for the first time.

Changelog: versioned changelog published with every API update. Format: date, affected endpoints, change type (breaking / additive / fix).