API Gleam

REST/JSON API Patterns (Gleam + Wisp)

Design patterns and conventions for building consistent, maintainable REST APIs in Gleam.

Stack Context

Core Principles

• REST nouns, not verbs — routes use plural nouns and sub-resources
• Canonical error shape — every error response uses {"error": "Kind", "message": "text"}
• Centralized error handling — never build ad-hoc JSON error responses in handlers
• Consistent serialization — shared helpers for timestamps, metadata, optional fields
• Middleware as closures — auth → rate limit → handler, each layer wraps the next

When to Apply

Reference these patterns when:

• Designing new API routes or renaming existing ones
• Returning error responses from handlers or middleware
• Implementing paginated list endpoints
• Serializing domain types to JSON
• Consolidating multiple GET or POST endpoints
• Handling validation errors vs decode errors
• Setting up SPA routing alongside API routes
• Composing middleware (auth, rate limiting, usage tracking)

Reference Categories by Priority

Token Efficiency

Follow references/token-efficiency.md rules. When reviewing or writing API code:

1. Grep for specific patterns (e.g., error_response.handle, wisp.require_json, hal.page) instead of reading all handler files
2. Use git diff --name-only to scope reviews to changed handler/router files only
3. Read targeted line ranges around Grep matches, not entire controllers

How to Use

Read individual reference files in references/ for detailed explanations and Gleam examples. Each reference contains:

• Brief explanation of the pattern and why it matters
• Incorrect example showing the anti-pattern
• Correct example showing the recommended approach
• When to apply and edge cases

Available References

Route Design (route-):

• references/route-naming.md

Error Handling (error-, validation-):

• references/error-responses.md
• references/validation-errors.md

Serialization (json-):

• references/json-serialization.md

Pagination (pagination-):

• references/pagination-hal.md

Request Dispatch (dispatch-):

• references/query-dispatch.md
• references/body-dispatch.md

Router Patterns (router-):

• references/spa-routing.md
• references/middleware-composition.md

Decision Tree

"I need to..."

• ...name a new route → route-naming.md
• ...return an error from a handler → error-responses.md
• ...distinguish 400 vs 422 → validation-errors.md
• ...add pagination to a list endpoint → pagination-hal.md
• ...serialize timestamps or metadata → json-serialization.md
• ...merge multiple GET endpoints → query-dispatch.md
• ...dispatch POST by body type → body-dispatch.md
• ...serve SPA alongside API → spa-routing.md
• ...compose auth + rate limiting → middleware-composition.md

9 reference files across 6 categories

References

• https://hexdocs.pm/wisp/
• https://hexdocs.pm/mist/
• https://hexdocs.pm/gleam_json/