Agent skill

API Design

Design or review REST/GraphQL APIs when endpoints or contracts change.

Install API Design

skills CLI

$ npx skills add KbWen/agentic-os --skill api-design -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI

$ gh skill install KbWen/agentic-os api-design --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy

$ git clone --depth 1 https://github.com/KbWen/agentic-os.git skills-src && mkdir -p .claude/skills && cp -r skills-src/.agents/skills/api-design .claude/skills/api-design && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Paste into Claude Code

Install the "api-design" agent skill from https://github.com/KbWen/agentic-os/tree/main/.agents/skills/api-design into .claude/skills/api-design/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "api-design", then confirm the skill loads.

Claude Code copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

$skill-installer

$skill-installer install https://github.com/KbWen/agentic-os/tree/main/.agents/skills/api-design

Type this inside Codex. $skill-installer <name> installs a curated skill from openai/skills. The installer writes to $CODEX_HOME/skills (default ~/.codex/skills). Restart Codex if the skill does not show up.

skills CLI

$ npx skills add KbWen/agentic-os --skill api-design -a codex

Project install goes to .agents/skills/; add -g for ~/.codex/skills/.

GitHub CLI

$ gh skill install KbWen/agentic-os api-design --agent codex

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/KbWen/agentic-os.git skills-src && mkdir -p .agents/skills && cp -r skills-src/.agents/skills/api-design .agents/skills/api-design && rm -rf skills-src

Use ~/.agents/skills/ instead of .agents/skills for a personal install.

Codex skills documentation · loads skills from .agents/skills/

Paste into Codex

Install the "api-design" agent skill from https://github.com/KbWen/agentic-os/tree/main/.agents/skills/api-design into .agents/skills/api-design/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "api-design", then confirm the skill loads.

Codex copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

skills CLI

$ npx skills add KbWen/agentic-os --skill api-design -a cursor

Project install goes to .agents/skills/; add -g for ~/.cursor/skills/.

GitHub CLI

$ gh skill install KbWen/agentic-os api-design --agent cursor

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/KbWen/agentic-os.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/.agents/skills/api-design .cursor/skills/api-design && rm -rf skills-src

Use ~/.cursor/skills/ instead of .cursor/skills for a personal install.

Cursor skills documentation · loads skills from .cursor/skills/, .agents/skills/, .claude/skills/, .codex/skills/

Paste into Cursor

Install the "api-design" agent skill from https://github.com/KbWen/agentic-os/tree/main/.agents/skills/api-design into .cursor/skills/api-design/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "api-design", then confirm the skill loads.

Cursor copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

gemini skills install

$ gemini skills install https://github.com/KbWen/agentic-os.git --path .agents/skills/api-design

--scope user (default) or --scope workspace; --path is the subfolder of the repo that holds the skill; --consent skips the security confirmation prompt.

skills CLI

$ npx skills add KbWen/agentic-os --skill api-design -a gemini-cli

Project install goes to .agents/skills/; add -g for ~/.gemini/skills/.

GitHub CLI

$ gh skill install KbWen/agentic-os api-design --agent gemini-cli

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/KbWen/agentic-os.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/.agents/skills/api-design .gemini/skills/api-design && rm -rf skills-src

Use ~/.gemini/skills/ instead of .gemini/skills for a personal install, then run /skills reload.

Gemini CLI skills documentation · loads skills from .gemini/skills/, .agents/skills/

Paste into Gemini CLI

Install the "api-design" agent skill from https://github.com/KbWen/agentic-os/tree/main/.agents/skills/api-design into .gemini/skills/api-design/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "api-design", then confirm the skill loads.

Gemini CLI copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

GitHub CLI

$ gh skill install KbWen/agentic-os api-design

Installs for Copilot at project scope by default; add --scope user for a personal install. Preview a skill first with gh skill preview. Needs GitHub CLI 2.90.0 or later (public preview).

skills CLI

$ npx skills add KbWen/agentic-os --skill api-design -a github-copilot

Project install goes to .agents/skills/; add -g for ~/.copilot/skills/.

Manual copy

$ git clone --depth 1 https://github.com/KbWen/agentic-os.git skills-src && mkdir -p .github/skills && cp -r skills-src/.agents/skills/api-design .github/skills/api-design && rm -rf skills-src

Use ~/.copilot/skills/ instead of .github/skills for a personal install. Commit .github/skills so cloud agent and code review can use it.

GitHub Copilot skills documentation · loads skills from .github/skills/, .claude/skills/, .agents/skills/

Paste into GitHub Copilot

Install the "api-design" agent skill from https://github.com/KbWen/agentic-os/tree/main/.agents/skills/api-design into .github/skills/api-design/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "api-design", then confirm the skill loads.

GitHub Copilot copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

skills CLI

$ npx skills add KbWen/agentic-os --skill api-design -a opencode

OpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.

GitHub CLI

$ gh skill install KbWen/agentic-os api-design --agent opencode

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/KbWen/agentic-os.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/.agents/skills/api-design .opencode/skills/api-design && rm -rf skills-src

Use ~/.config/opencode/skills/ instead of .opencode/skills for a personal install.

OpenCode skills documentation · loads skills from .opencode/skills/, .claude/skills/, .agents/skills/

Paste into OpenCode

Install the "api-design" agent skill from https://github.com/KbWen/agentic-os/tree/main/.agents/skills/api-design into .opencode/skills/api-design/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "api-design", then confirm the skill loads.

OpenCode copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

Facts

Skill name: api-design
GitHub stars: 206
Token cost: ~1k tokens
SKILL.md length: 422 words
Files: 2
Skills in repo: 12
Repo updated: Oct 6, 2026
First seen: Oct 7, 2026
Licence: MIT

At a glance

Design or review REST/GraphQL APIs when endpoints or contracts change.

Tasks that involve API design
SKILL.md covers When to Apply, Conventions, Checklist and Heading-Scoped Read Note, plus 2 more sections
Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md
Tasks that involve GraphQL

What it does

API Design is an agent skill from KbWen/agentic-os. Design or review REST/GraphQL APIs when endpoints or contracts change.

Its SKILL.md is about 1k tokens, which your agent loads only when the skill is triggered. The skill folder holds 2 other files (for example `agents/openai.yaml`).

It sits in Backend & APIs, covering API design and GraphQL. The repository describes itself as: Governance framework for AI coding agents. It runs them through a five-step workflow (plan, build, review, test, ship) where no step counts as done without evidence. Drop-in… The licence is MIT.

When your agent uses it

Tasks that involve API design
Tasks that involve GraphQL

Example prompts

“/api-design”

What it can do on your machine

Read from SKILL.md and the folder at commit 81a4034. It shows what the files ask for, not the result of running them.

Tool permissions
Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.
From allowed-tools in the SKILL.md frontmatter.
Runs code
No scripts in the folder and no shell commands in SKILL.md (its code samples are json).
From the folder's file list and the shell code blocks in SKILL.md.
Network
No URLs in SKILL.md.
From URLs in SKILL.md, links to its own repository left out.
Credentials
Names no API keys, tokens, secrets or passwords.
From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

API Design loads about 1k tokens when it runs. Until then it costs about 20 tokens; SKILL.md has 422 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it: ~20
When it runs · the whole SKILL.md, loaded when a task matches: ~1k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check passed

The automated check found no risky patterns in SKILL.md.

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from KbWen/agentic-os at commit 81a4034, republished under its MIT licence (© KbWen). 422 words, ~1,017 tokens.

Download SKILL.mdSave it as .claude/skills/api-design/SKILL.md (or your agent's skills folder). This skill also uses 1 other file; get the full folder from GitHub.

name: api-design
description: Design or review REST/GraphQL APIs when endpoints or contracts change.

<!-- This is a SCAFFOLD skill -->

API Design

When to Apply

Classification: feature, architecture-change, hotfix (if touching API endpoints)
Phase: /implement (design & build), /review (compliance check), /test (contract verification)
Trigger: Task involves creating, modifying, or deprecating API endpoints

Conventions

Customize after /app-init: Replace these generic conventions with your project's ADR decisions.

Endpoint Naming

Use nouns for resources, not verbs: GET /users not GET /getUsers
Plural resource names: /users, /orders, /products
Nested resources for relationships: /users/:id/orders
Use kebab-case for multi-word paths: /order-items

HTTP Methods

Action	Method	Success Status	Idempotent
List	GET	200	Yes
Get one	GET	200	Yes
Create	POST	201	No
Full update	PUT	200	Yes
Partial update	PATCH	200	No
Delete	DELETE	204	Yes

Error Response Format

json

{
  "error": {
    "code": "VALIDATION_ERROR",
    "message": "Email is required",
    "details": {
      "field": "email",
      "constraint": "required"
    }
  }
}

Standard Error Codes

HTTP Status	When	Error Code Pattern
400	Invalid input	VALIDATION_ERROR, INVALID_FORMAT
401	Not authenticated	UNAUTHORIZED
403	Not permitted	FORBIDDEN
404	Resource not found	NOT_FOUND
409	Conflict (duplicate)	CONFLICT, DUPLICATE
422	Business rule violation	UNPROCESSABLE
429	Rate limited	RATE_LIMITED
500	Server error	INTERNAL_ERROR

Pagination

json

{
  "data": [...],
  "pagination": {
    "total": 100,
    "page": 1,
    "per_page": 20,
    "has_next": true
  }
}

Versioning

URL path versioning: /api/v1/users
Breaking changes require new version
Deprecation: add Sunset header with date, keep old version for N months

Input Validation

Validate at the controller/route level BEFORE business logic
Return ALL validation errors at once (batch), not one at a time
Sanitize strings: trim whitespace, escape HTML where applicable
Enforce max lengths on all string fields

Show full SKILL.md (205 more words)Show less

Checklist

During /implement:

Every endpoint has input validation
Every endpoint returns consistent error format
Every endpoint has proper auth check (or explicit public annotation)
Pagination for list endpoints
Rate limiting consideration (at least documented in spec)
No sensitive data in URL parameters (use body or headers)
Request/response examples in spec match implementation

During /review:

No N+1 query patterns in list endpoints
Proper HTTP status codes (not everything is 200)
Idempotency for PUT/DELETE
Error messages don't leak internal details (stack traces, SQL, paths)
CORS configured per ADR policy

Heading-Scoped Read Note

For phase-entry loading, read only:

When to Apply
Checklist

Load Conventions, Anti-Patterns, and References on full read or cache miss only.

Anti-Patterns

God endpoint: One endpoint that does everything based on query params. Split into specific endpoints.
Verb in URL: POST /createUser → POST /users
Inconsistent naming: Mixing /user and /products (singular vs plural)
Swallowing errors: Catching exceptions and returning 200 with { success: false }
Leaking internals: Returning DB column names directly as API fields without mapping
Missing 404: Returning empty 200 instead of 404 when resource doesn't exist
Unbounded lists: List endpoints without pagination or default limits

References

Project ADR: docs/adr/ADR-002-project-architecture.md § API Design
Security guardrails: .agent/rules/security_guardrails.md (A01: Access Control, A03: Injection)
Spec template: .agentcortex/templates/spec-app-feature.md § API Contract

Files

SKILL.md and 1 other file in .agents/skills/api-design of KbWen/agentic-os.

SKILL.md
agents/openai.yaml

Open the folder on GitHubat commit 81a4034

Compare with similar skills

API Design next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

API Design compared with similar skills
Skill	Stars	Used in	Tokens	Auto-check	Licence	Repo updated
API Design this skillKbWen/agentic-os	206	—	~1k	Automated safety check: Pass	MIT	yesterday
API DesignerJeffallan/claude-skills	12k	2 repos	~2k	Automated safety check: Pass	MIT	4 days ago
Nodejs Backend Patternsever-works/ever-works	158	17 repos	~4k	Automated safety check: Pass	AGPL-3.0	2 days ago
API And Interface Designdzhalaevd/Donatello	135	9 repos	~2.6k	Automated safety check: Pass	Apache-2.0	4 days ago
API Design Principlesjh941213/my-cc-harness	126	19 repos	~3.4k	Automated safety check: Pass	None	2 mo ago
Designing APIsCloudAI-X/claude-workflow-v2	1.4k	2 repos	~1.2k	Automated safety check: Pass	MIT	yesterday

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Questions about API Design

What does API Design do?

Design or review REST/GraphQL APIs when endpoints or contracts change. API Design is an agent skill from KbWen/agentic-os. Design or review REST/GraphQL APIs when endpoints or contracts change.

When should I use API Design?

API Design fits situations like: tasks that involve API design; tasks that involve GraphQL.

How do I install API Design in Claude Code?

Run `npx skills add KbWen/agentic-os --skill api-design -a claude-code`. Or copy the skill folder (.agents/skills/api-design in KbWen/agentic-os) into .claude/skills/api-design in your project. Claude Code loads it when a task matches its description.

How do I install API Design in Codex?

Run `npx skills add KbWen/agentic-os --skill api-design -a codex`. Or copy the skill folder (.agents/skills/api-design in KbWen/agentic-os) into .agents/skills/api-design in your project. Codex loads it when a task matches its description.

Can I use API Design in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add KbWen/agentic-os --skill api-design -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/api-design, .gemini/skills/api-design, .github/skills/api-design and .opencode/skills/api-design in your project.

What does API Design need to run?

SKILL.md names no scripts, command-line tools or credentials: API Design is instructions for the agent only.

Does API Design access the network?

SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.

Is API Design safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.

What licence does API Design use?

API Design is published under the MIT licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does API Design use?

About 1k tokens (SKILL.md is roughly 4.1k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.

What are the alternatives to API Design?

Skills that share tags, products or a category with API Design: API Designer (Jeffallan/claude-skills, 12k stars), Nodejs Backend Patterns (ever-works/ever-works, 158 stars), API And Interface Design (dzhalaevd/Donatello, 135 stars) and API Design Principles (jh941213/my-cc-harness, 126 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains API Design?

KbWen (a GitHub user) maintains it in KbWen/agentic-os, which has 206 GitHub stars. The repository holds 12 skills in this directory. The repository was last updated on October 6, 2026.

Source: KbWen/agentic-os on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.

Install API Design

Facts

At a glance

What it does

When your agent uses it

Example prompts

What it can do on your machine

Tool permissions

Runs code

Network

Credentials

Context cost

Safety

SKILL.md

API Design

When to Apply

Conventions

Endpoint Naming

HTTP Methods

Error Response Format

Standard Error Codes

Pagination

Versioning

Input Validation

Checklist

Heading-Scoped Read Note

Anti-Patterns

References

Files

Compare with similar skills

Similar skills

More from KbWen/agentic-os

Related

Questions about API Design