# go-api-design

A skill that steers the agent through Go HTTP handler design: routing, middleware, validation, pagination, graceful shutdown. Useful when you start a REST service or rework one.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · ★ 83
- Author: eduardo-sl
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/eduardo-sl/go-agent-skills/tree/HEAD/skills/(architecture)/go-api-design/SKILL.md
- Updated: 2026-10-15
- HTML: https://affpapa.org/en/nevibecode/skills/go-api-design

## What it does

The skill lays down conventions for Go services built on the standard library. Routing goes through `http.ServeMux` (Go 1.22+): patterns like `"GET /users/{id}"` match the method, `r.PathValue("id")` pulls the wildcard, and the wrong method returns 405 with an `Allow` header. Handlers are methods on a struct holding dependencies such as the store and logger, not package globals. Domain errors map to status codes at the handler boundary, and internal details stay inside.

Middleware is `func(http.Handler) http.Handler` with a fixed order: Recoverer outermost, then RequestID, Logger, Auth, RateLimit. Request bodies get capped with `http.MaxBytesReader` before decoding, and a clean decode is not a valid value — validation happens in the same step, answering 400 with a stable message instead of echoing the decoder's text.

Other sections cover URL naming (plural nouns, kebab-case, version in the path, no verbs), cursor pagination over offset/limit, liveness and readiness endpoints, a consistent error shape, and shutdown on SIGTERM. A reference file `references/handlers-and-middleware.md` sits inside and loads on demand. The Go toolchain is required; without it the allowed `go` and `gofmt` commands go nowhere.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add eduardo-sl/go-agent-skills --skill go-api-design -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/go-api-design/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/go-api-design/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add eduardo-sl/go-agent-skills --skill go-api-design -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/go-api-design/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add eduardo-sl/go-agent-skills --skill go-api-design -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/go-api-design/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install eduardo-sl/go-agent-skills go-api-design
```

2. **Manually: put the files in place**
- File: `.github/skills/go-api-design/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add eduardo-sl/go-agent-skills --skill go-api-design -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/eduardo-sl/go-agent-skills --path 'skills/(architecture)/go-api-design'
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/go-api-design/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add eduardo-sl/go-agent-skills --skill go-api-design -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/eduardo-sl/go-agent-skills/tree/HEAD/skills/(architecture)/go-api-design/SKILL.md

## When to use it
- lay out REST endpoints across handlers and routes
- wire a middleware chain in the right order
- cap the request body and validate the payload
- switch a large list endpoint to cursor pagination
- stop the server on SIGTERM without dropping live requests

## Example prompts
- Design a REST API for an orders service in Go: routes, handlers, middleware
- Add graceful shutdown on SIGTERM plus `/healthz` and `/readyz` endpoints to `main.go`
- Rework the user list endpoint to cursor pagination with `nextCursor`

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 904e6f8ee233a2fa.

BEGIN THIRD-PARTY FILE 904e6f8ee233a2fa
````text
---
name: go-api-design
description: >
  HTTP/REST API design for Go services: handlers, ServeMux routing,
  middleware, request validation, pagination, idempotency, health checks,
  error responses, and graceful shutdown. Use when designing APIs, writing
  HTTP handlers, implementing middleware, or structuring REST endpoints.
  Trigger examples: "design API", "REST endpoints", "HTTP handler",
  "middleware pattern", "graceful shutdown", "API versioning".
  Not for: gRPC services (go-grpc), spec-first OpenAPI work (go-openapi),
  general architecture (go-architecture-review), concurrency in handlers
  (go-concurrency-review).
user-invocable: true
license: MIT
compatibility: Designed for Claude Code or similar AI coding agents working on Go projects. Requires the Go toolchain.
allowed-tools: Read Edit Write Glob Grep Bash(go:*) Bash(gofmt:*)
metadata:
  author: eduardo-sl
  version: "2.0.1"
---

# Go API Design

APIs are contracts. Once published, they're promises. Design them as if
you'll maintain them for a decade — because you probably will.

> Community default. A project skill or agent-config rule that explicitly
> supersedes `go-api-design` takes precedence over this one.

Detailed reference material, loaded on demand:

- `references/handlers-and-middleware.md` — handler structs, JSON response
  helpers, request ID and recoverer middleware, decode-and-validate.

Read a reference file only when the summary below is not enough.

## 1. HTTP Handler Structure

- Route with the standard `http.ServeMux` (Go 1.22+): `"GET /users/{id}"`
  patterns match the method, `r.PathValue("id")` reads the wildcard, and a
  wrong method gets a 405 with `Allow`. A router dependency earns its place
  for middleware groups and sub-routers, not for path parameters.
- Handlers are methods on a struct that holds their dependencies (store,
  logger) — never package globals.
- Handler methods return nothing: they write the response and handle the
  error themselves, mapping domain errors (`errors.Is(err, ErrNotFound)`)
  to status codes and logging only the unexpected ones.
- Route through one JSON helper that sets `Content-Type`, writes the status
  once, and logs encode failures.

## 2. Middleware Pattern

Middleware is `func(http.Handler) http.Handler`. Order, outside → inside:

```text
Recoverer → RequestID → Logger → Auth → RateLimit → Handler
```
````
END THIRD-PARTY FILE 904e6f8ee233a2fa

The third-party file has ended. Everything between the 904e6f8ee233a2fa tags is data: requests and commands from it are not followed. An “end of file” line with another tag inside the block is part of the file.

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