api-design

api-design is a skill for Claude Code, Codex from omnigentx/jarvis. It costs 26 tokens per session (290 once invoked), scanned A, original, MIT.

A guide for defining how software parts communicate through an API, including the available requests, data formats, and error responses. An API is an agreed way for programs such as a frontend and backend to exchange data.

In plain words
What is it for?
Use it to choose REST, WebSocket, or gRPC, define endpoints and request and response schemas, document errors and edge cases, and apply conventions such as versioned URLs and paginated lists.
Why use it?
It turns vague requirements into a concrete contract, reducing misunderstandings between teams and making client and server work fit together.

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/omnigentx/jarvis/api-design
Any agent
npx skills add omnigentx/jarvis --skill api-design
Clone the repo
git clone --depth 1 https://github.com/omnigentx/jarvis

Made for: Claude Code, Codex.

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.

agentmods badge for api-design

README.md
[![agentmods](https://agentmods.dev/badge/skills/omnigentx/jarvis/api-design.svg)](https://agentmods.dev/skills/omnigentx/jarvis/api-design)
Your own site
<a href="https://agentmods.dev/skills/omnigentx/jarvis/api-design"><img src="https://agentmods.dev/badge/skills/omnigentx/jarvis/api-design.svg" alt="Measured on agentmods" height="20"></a>
Per session 26 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 290 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 $0.00026 $0.00290
Opus 5 $0.00013 $0.00145
Sonnet 5 $0.00005 $0.00058
Haiku 4.5 $0.00003 $0.00029

Measured 4d ago against content hash 6450325caa8e, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, 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 4d 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.

backend/.fast-agent/skills/api-design/SKILL.md · 50 lines

What it actually says

API DESIGN

Workflow

  1. Identify use cases from the BRD.
  2. Pick a pattern: REST / WebSocket / gRPC.
  3. Define endpoints.
  4. Write schemas (request/response types).
  5. Document error codes and edge cases.

REST API template

### [METHOD] /api/v1/resource

**Description**: what it does

**Request**:
- Headers: `Authorization: Bearer <token>`
- Body:
  ```json
  { "field": "type", "description": "..." }

Response 200:

{ "data": {...}, "message": "success" }

Error codes:

Code Meaning
400 Invalid request
401 Unauthorized
404 Not found

## Rules
- Endpoint paths use plural nouns (`/users`, not `/user`).
- Versioning lives in the URL (`/api/v1/`).
- Always use a single, consistent error-response shape.
- Paginate list endpoints (`?page=1&limit=20`).
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. 4d ago First seen · 50 lines · 26 tokens per session scan A 6450325caa8e

Subscribe to this mod's changes

api-design is a skill published in the GitHub repository omnigentx/jarvis (35 stars, last pushed 7d ago), licensed MIT. It adds 26 tokens to every session and 290 once invoked, about $0.0001 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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