What is api-designer?

An API design guide for planning REST and GraphQL interfaces, including their structure, rules, and documentation.

Use it to design resources, URLs, schemas, authentication, pagination, rate limits, and OpenAPI documentation for a new or existing API.

It helps prevent inconsistent endpoints, unclear errors, and breaking changes that make APIs difficult to use and maintain.

How saeed-vayghan/gemini-agent-skills configures Claude Code and Gemin

Reuse

Borrowing it

Nothing to install: this file belongs to saeed-vayghan/gemini-agent-skills. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file

curl -O https://raw.githubusercontent.com/saeed-vayghan/gemini-agent-skills/master/.gemini/skills/api-designer/SKILL.md

Clone the repo

git clone --depth 1 https://github.com/saeed-vayghan/gemini-agent-skills

Made for: Claude Code, Gemini CLI.

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/saeed-vayghan/gemini-agent-skills/api-designer/github.svg)](https://agentmods.dev/skills/saeed-vayghan/gemini-agent-skills/api-designer)

Your own site

<a href="https://agentmods.dev/skills/saeed-vayghan/gemini-agent-skills/api-designer"><img src="https://agentmods.dev/badge/skills/saeed-vayghan/gemini-agent-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/skills/saeed-vayghan/gemini-agent-skills/api-designer"><img src="https://agentmods.dev/badge/skills/saeed-vayghan/gemini-agent-skills/api-designer.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 34 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 1,079 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	$0.00034	$0.01079
Opus 5	$0.00017	$0.00540
Sonnet 5	$0.00007	$0.00216
Haiku 4.5	$0.00003	$0.00108

Measured 12d ago against content hash 5dfba6a55f76, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-12, 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 12d 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.

.gemini/skills/api-designer/SKILL.md · 216 lines

How it starts

The opening of the file, as written. The whole thing — 216 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 · 216 lines

Files

What ships with it

2 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

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.

12d ago First seen · 216 lines · 34 tokens per session scan A 5dfba6a55f76

Subscribe to this mod's changes

api-designer is a skill published in the GitHub repository saeed-vayghan/gemini-agent-skills (34 stars, last pushed 7mo ago), licensed MIT. It adds 34 tokens to every session and 1,079 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.

Backend and APIs agent-skills agents ai antigravity gemini

gemini-agent-skills: Skill for Claude Code

Borrowing it

Wrote this? Show the measurements

What it costs to keep this loaded

Grade A, and why

Nothing flagged

How it starts

Communication Protocol

What ships with it

What this file has done since we first saw it

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