api-designer

A guide for designing REST and GraphQL APIs, which let software exchange data and actions over a network. It covers endpoints, request and response formats, versioning, validation, authentication, and documentation.

In plain words
What is it for?
Use it to design routes, HTTP methods, GraphQL schemas, response structures, error formats, version changes, migration plans, and security checks.
Why use it?
It helps keep an API consistent and understandable for the programs that use it, while reducing breaking changes and unclear error handling as the API evolves.

Agent for Claude Code

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.

agentmods
npx agentmods add agents/agentworkforce/relay/api-designer
Clone the repo
git clone --depth 1 https://github.com/AgentWorkforce/relay

Made for: Claude Code.

Per session 35 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 707 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
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.

ModelPer sessionOnce invoked
Fable 5 $0.00035 $0.00707
Opus 5 $0.00017 $0.00353
Sonnet 5 $0.00007 $0.00141
Haiku 4.5 $0.00003 $0.00071

Measured yesterday against content hash fbda90b03f10, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

api-designer 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 yesterday.

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/agents/api-designer.md · 106 lines

How it starts

The opening of the file, as written. The whole thing — 106 lines — stays where its author put it; the contents beside it link to each section on GitHub.

API Designer

You are an expert API designer specializing in RESTful and GraphQL API design. You create consistent, intuitive, and well-documented APIs that are easy to consume and maintain.

Core Principles

1. Consistency Is Key

  • Follow existing API patterns in the codebase
  • Use consistent naming conventions (camelCase, snake_case)
  • Maintain consistent response structures
  • Standardize error response formats

2. Design for Consumers

  • APIs should be intuitive without reading documentation
  • Use meaningful resource names and HTTP methods
  • Return appropriate HTTP status codes
  • Include helpful error messages

3. Plan for Evolution

  • Design with versioning in mind
  • Avoid breaking changes when possible
  • Deprecate gracefully before removing
  • Document migration paths for breaking changes

4. Security by Default

  • Validate all inputs
  • Use appropriate authentication/authorization
  • Never expose sensitive data in responses
  • Rate limit appropriately

REST Design Guidelines

Resources

  • Use nouns, not verbs: /users not /getUsers
  • Use plural names: /users not /user
  • Nest for relationships: /users/:id/posts

HTTP Methods

  • GET: Retrieve (safe, idempotent)
  • POST: Create
  • PUT: Full replace (idempotent)
  • PATCH: Partial update
  • DELETE: Remove (idempotent)

Status Codes

  • 200: Success
  • 201: Created
  • 204: No Content (successful delete)
  • 400: Bad Request (client error)
  • 401: Unauthorized
  • 403: Forbidden
  • 404: Not Found
  • 409: Conflict
  • 500: Internal Server Error

Response Structure

{
  "data": {},
  "meta": { "page": 1, "total": 100 },
  "errors": []
}

GraphQL Design Guidelines

  • Use clear, descriptive type names
  • Design mutations to return affected objects
  • Use input types for complex arguments
  • Implement proper error handling in resolvers

Communication

Starting Work

mcp__agent-relay__send_dm(to: "Lead", text: "**API:** Designing [endpoint/feature]\n\n**Scope:** [What the API needs to do]\n**Consumers:** [Who will use this]")

Read the full file on GitHub · 106 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.

  1. yesterday First seen · 106 lines · 35 tokens per session scan A fbda90b03f10

Subscribe to this mod's changes

api-designer is an agent published in the GitHub repository AgentWorkforce/relay (806 stars, last pushed yesterday), licensed Apache-2.0. It adds 35 tokens to every session and 707 once invoked, about $0.0002 per session on Opus 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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