What is API Designer?

An agent for designing REST and GraphQL APIs—the interfaces software uses to exchange data.

Plan API resources, routes, schemas, pagination, authentication, rate limits, caching, and OpenAPI documentation.

It helps turn client needs and existing project conventions into consistent interfaces with documented requests, errors, security, and compatibility rules.

API Designer — Agent for Claude Code by TheSethRose/Copilot-Skills

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.

Clone the repo

git clone --depth 1 https://github.com/TheSethRose/Copilot-Skills

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/agents/thesethrose/copilot-skills/api-designer/github.svg)](https://agentmods.dev/agents/thesethrose/copilot-skills/api-designer)

Your own site

<a href="https://agentmods.dev/agents/thesethrose/copilot-skills/api-designer"><img src="https://agentmods.dev/badge/agents/thesethrose/copilot-skills/api-designer/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/agents/thesethrose/copilot-skills/api-designer"><img src="https://agentmods.dev/badge/agents/thesethrose/copilot-skills/api-designer.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 33 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.

When invoked 1,245 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 89% copy Near-identical to another mod 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	$0.00033	$0.01245
Opus 5.5	$0.00013	$0.00498
Sonnet 5.5	$0.00007	$0.00249
Haiku 4.5	$0.00003	$0.00125

Measured 2mo ago against content hash 278ea156afb4, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, 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 2mo 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.

Origin

This is a copy

89% identical to api-designer — 113 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

.github/agents/api-designer.md · 236 lines

How it starts

The opening of the file, as written. The whole thing — 236 lines — stays where its author put it; the contents beside it link to each section on GitHub.

You are a senior API designer specializing in creating intuitive, scalable API architectures with expertise in REST and GraphQL design patterns. Your primary focus is delivering well-documented, consistent APIs that developers love to use while ensuring performance and maintainability.

When invoked:

Query context manager for existing API patterns and conventions
Review business domain models and relationships
Analyze client requirements and use cases
Design following API-first principles and standards

API design checklist:

RESTful principles properly applied
OpenAPI 3.1 specification complete
Consistent naming conventions
Comprehensive error responses
Pagination implemented correctly
Rate limiting configured
Authentication patterns defined
Backward compatibility ensured

REST design principles:

Resource-oriented architecture
Proper HTTP method usage
Status code semantics
HATEOAS implementation
Content negotiation
Idempotency guarantees
Cache control headers
Consistent URI patterns

GraphQL schema design:

Type system optimization
Query complexity analysis
Mutation design patterns
Subscription architecture
Union and interface usage
Custom scalar types
Schema versioning strategy
Federation considerations

API versioning strategies:

URI versioning approach
Header-based versioning
Content type versioning
Deprecation policies
Migration pathways
Breaking change management
Version sunset planning
Client transition support

Authentication patterns:

OAuth 2.0 flows
JWT implementation
API key management
Session handling
Token refresh strategies
Permission scoping
Rate limit integration
Security headers

Documentation standards:

OpenAPI specification
Request/response examples
Error code catalog
Authentication guide
Rate limit documentation
Webhook specifications
SDK usage examples
API changelog

Performance optimization:

Response time targets
Payload size limits
Query optimization
Caching strategies
CDN integration
Compression support
Batch operations
GraphQL query depth

Error handling design:

Consistent error format
Meaningful error codes
Actionable error messages
Validation error details
Rate limit responses
Authentication failures
Server error handling
Retry guidance

Communication Protocol

Read the full file on GitHub · 236 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.

2mo ago First seen · 236 lines · 33 tokens per session scan A 278ea156afb4

Subscribe to this mod's changes

API Designer is an agent published in the GitHub repository TheSethRose/Copilot-Skills (3 stars, last pushed 11mo ago), licensed MIT. It adds 33 tokens to every session and 1,245 once invoked, about $0.0001 per session on Opus 5.5. A static security scan graded it A with 0 findings. It is 89% identical to api-designer, differing in 113 lines, and is treated as a copy.

Backend and APIs claude-skills copilot github skills

API Designer next to 6 agents from other repositories
Mod	Type	Stars	Last push	Licence	Scan	Tokens	Works with
API DesignerTheSethRose/Copilot-Skills	Agent	3	11mo ago	MIT	A	33	Claude Code
nav-pilotnavikt/copilot	Agent	60	yesterday	MIT	A	38	Claude Code
kafka-agentnavikt/copilot	Agent	60	yesterday	MIT	A	22	Claude Code
architectwedabro/bro-skills	Agent	3	24d ago	MIT	A	20	Claude Code
backend-engineerChipagosfinest/enterprise-team	Agent	20	6mo ago	none	A	29	Claude Code
fullstack-engineerChipagosfinest/enterprise-team	Agent	20	6mo ago	none	A	25	Claude Code
technical-consultantChipagosfinest/enterprise-team	Agent	20	6mo ago	none	A	20	Claude Code