A guide to designing REST and GraphQL APIs. APIs are interfaces that let software systems exchange data; REST and GraphQL are two common ways to structure them.

Use it when creating or reviewing API contracts, including routes, request and response data, login rules, filtering, pagination, and versioning.

It helps prevent unclear endpoints, inconsistent data formats, weak input checks, and confusing authentication or version changes.

api-design — Skill for Claude Code by tranhieutt

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent

npx skills add tranhieutt/software_development_department --skill api-design

Clone the repo

git clone --depth 1 https://github.com/tranhieutt/software_development_department

Made for: Claude Code.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/skills/tranhieutt/software_development_department/api-design/github.svg)](https://agentmods.dev/skills/tranhieutt/software_development_department/api-design)

Your own site

<a href="https://agentmods.dev/skills/tranhieutt/software_development_department/api-design"><img src="https://agentmods.dev/badge/skills/tranhieutt/software_development_department/api-design/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/skills/tranhieutt/software_development_department/api-design"><img src="https://agentmods.dev/badge/skills/tranhieutt/software_development_department/api-design.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 53 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 920 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5.1	$0.00053	$0.00920
Opus 5.5	$0.00021	$0.00368
Sonnet 5.5	$0.00011	$0.00184
Haiku 4.5	$0.00005	$0.00092

Measured 1mo ago against content hash 38a7a3d289bb, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

api-design scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.claude/skills/api-design/SKILL.md · 101 lines

How it starts

The opening of the file, as written. The whole thing — 101 lines — stays where its author put it; the contents beside it link to each section on GitHub.

When this skill is invoked:

Read the target API spec or route files in full.

For API design in an existing domain, SHOULD also inspect docs/technical/API.md, related design/specs/*, related design/contracts/* if present, and recent relevant ledger entries via /trace-history. This is advisory unless the change is an ADR, coordination-rule change, high-risk retry, or protocol removal.
Identify the API type (REST, GraphQL, WebSocket) and apply appropriate standards.
Evaluate REST design quality (if REST):
- Resources use nouns, not verbs (/users, not /getUsers)
- Correct HTTP methods (GET=read, POST=create, PUT/PATCH=update, DELETE=remove)
- Consistent plural resource naming (/users, /orders)
- Nested resources have max 2-3 levels of depth
- Query parameters used for filtering, sorting, pagination (not in path)
Evaluate request/response schemas:
- All inputs are validated and typed
- Responses are consistent in structure (envelope format if used)
- Pagination is consistent (cursor or page-based, not mixed)
- Timestamps in ISO 8601 (UTC)
- Money values in smallest currency unit (cents), not floats
Evaluate authentication & authorization:
- Every endpoint has explicit auth requirement documented
- Authorization is checked server-side, not just on the client
- Sensitive data not leaked in error messages
Evaluate error responses:
- Consistent error format (RFC 7807 Problem Details recommended)
- HTTP status codes used correctly (400 for client errors, 500 for server)
- Error messages are user-safe (no stack traces, SQL errors)
Evaluate versioning & backward compatibility:
- Breaking changes require a version bump
- Deprecation policy documented
- Clients can negotiate API version
Output the review:

## API Design Review: [API/Endpoint Name]

### REST Design: [CLEAN / ISSUES FOUND]
[List specific issues with examples]

### Schema Quality: [CLEAN / ISSUES FOUND]
[List schema inconsistencies or problems]

### Auth & Security: [SECURE / ISSUES FOUND]
[List authentication and authorization issues]

### Error Handling: [CONSISTENT / ISSUES FOUND]
[List error response problems]

### Versioning: [HANDLED / UNADDRESSED]
[Notes on breaking change risk]

### Positive Observations
[What is well-designed]

### Required Changes
[Must-fix items before shipping]

### Suggestions
[Nice-to-have improvements]

### Verdict: [APPROVED / APPROVED WITH SUGGESTIONS / CHANGES REQUIRED]

Protocol

Question: Auto-starts from argument (path to API spec or route files); no clarification needed
Options: Skip — single review path
Decision: Skip — verdict is advisory
Draft: Full review report shown in conversation only
Approval: Skip — read-only; no files written

Read the full file on GitHub · 101 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

1mo ago First seen · 101 lines · 53 tokens per session scan A 38a7a3d289bb

Subscribe to this mod's changes

api-design is a skill published in the GitHub repository tranhieutt/software_development_department (73 stars, last pushed 5mo ago), licensed MIT. It adds 53 tokens to every session and 920 once invoked, about $0.0002 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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Proactive architecture review — explore codebase structure, generate a self-contained HTML report with Mermaid diagrams and candidate improvements, then grill the findings. Use when planning a large refactor, onboarding to an unfamiliar codebase, or before a major architectural change.

datit309/supergraph · 52 tokens

api-design

Getting it into your agent

Wrote this? Show the measurements

What it costs to keep this loaded

Grade A, and why

Nothing flagged

How it starts

Protocol

What this file has done since we first saw it

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