api-patterns

Guidance for designing APIs, the interfaces through which programs exchange data. It compares REST, GraphQL, and tRPC and covers responses, authentication, versioning, pagination, rate limits, documentation, and security testing.

In plain words
What is it for?
Use it when planning API structure, response formats, authentication, pagination, version changes, rate limiting, OpenAPI documentation, or security checks.
Why use it?
It helps choose an API style and make decisions about how clients access, secure, document, and evolve the interface.

Skill for Claude CodeCodex

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 skills/diillson/chatcli/api-patterns
Any agent
npx skills add diillson/chatcli --skill api-patterns
Clone the repo
git clone --depth 1 https://github.com/diillson/chatcli

Made for: Claude Code, Codex.

Per session 28 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 581 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin 86% 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.

ModelPer sessionOnce invoked
Fable 5 $0.00028 $0.00581
Opus 5 $0.00014 $0.00291
Sonnet 5 $0.00006 $0.00116
Haiku 4.5 $0.00003 $0.00058

Measured yesterday against content hash d8c2cbe8a096, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

api-patterns 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.

The scan reads SKILL.md. This mod also ships 1 executable file (scripts/api_validator.py), listed below but not scanned — reading those needs a real analyzer, not pattern matching.

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

86% identical to api-patterns — 8 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.

.agent/skills/api-patterns/SKILL.md · 82 lines

How it starts

The opening of the file, as written. The whole thing — 82 lines — stays where its author put it; the contents beside it link to each section on GitHub.

API Patterns

API design principles and decision-making for 2025. Learn to THINK, not copy fixed patterns.

🎯 Selective Reading Rule

Read ONLY files relevant to the request! Check the content map, find what you need.


📑 Content Map

File Description When to Read
api-style.md REST vs GraphQL vs tRPC decision tree Choosing API type
rest.md Resource naming, HTTP methods, status codes Designing REST API
response.md Envelope pattern, error format, pagination Response structure
graphql.md Schema design, when to use, security Considering GraphQL
trpc.md TypeScript monorepo, type safety TS fullstack projects
versioning.md URI/Header/Query versioning API evolution planning
auth.md JWT, OAuth, Passkey, API Keys Auth pattern selection
rate-limiting.md Token bucket, sliding window API protection
documentation.md OpenAPI/Swagger best practices Documentation
security-testing.md OWASP API Top 10, auth/authz testing Security audits

Need Skill
API implementation @[skills/backend-development]
Data structure @[skills/database-design]
Security details @[skills/security-hardening]

✅ Decision Checklist

Before designing an API:

  • Asked user about API consumers?
  • Chosen API style for THIS context? (REST/GraphQL/tRPC)
  • Defined consistent response format?
  • Planned versioning strategy?
  • Considered authentication needs?
  • Planned rate limiting?
  • Documentation approach defined?

❌ Anti-Patterns

DON'T:

  • Default to REST for everything
  • Use verbs in REST endpoints (/getUsers)
  • Return inconsistent response formats
  • Expose internal errors to clients
  • Skip rate limiting

DO:

  • Choose API style based on context
  • Ask about client requirements
  • Document thoroughly
  • Use appropriate status codes

Read the full file on GitHub · 82 lines

Files

What ships with it

11 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.

  1. yesterday First seen · 82 lines · 28 tokens per session scan A d8c2cbe8a096

Subscribe to this mod's changes

api-patterns is a skill published in the GitHub repository diillson/chatcli (89 stars, last pushed 2d ago), licensed Apache-2.0. It adds 28 tokens to every session and 581 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it A with 0 findings. It is 86% identical to api-patterns, differing in 8 lines, and is treated as a copy.