api-designer

api-designer is an agent for Claude Code from pedrol-cmd/brain-drin. It costs 41 tokens per session (368 once invoked), scanned A, original, MIT.

An assistant for designing APIs, the defined ways that software systems exchange requests and data. It covers REST, GraphQL, gRPC, and WebSocket interfaces.

In plain words
What is it for?
Use it to design APIs, write OpenAPI or schema definitions, plan versioning, document endpoints, and create mock servers.
Why use it?
It helps turn integration needs into consistent endpoints, data schemas, error handling, security rules, and documentation.

Agent for Claude Code

Written for Claude Code: installed under .claude/. Also seen: model in frontmatter.

Good fit Use it to design APIs, write OpenAPI or schema definitions, plan versioning, document endpoints, and create mock servers.

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Install with agentmods
npx agentmods add agents/pedrol-cmd/brain-drin/api-designer
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/pedrol-cmd/brain-drin

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.

agentmods badge for api-designer

README.md
[![agentmods](https://agentmods.dev/badge/agents/pedrol-cmd/brain-drin/api-designer/github.svg)](https://agentmods.dev/agents/pedrol-cmd/brain-drin/api-designer)
Your own site
<a href="https://agentmods.dev/agents/pedrol-cmd/brain-drin/api-designer"><img src="https://agentmods.dev/badge/agents/pedrol-cmd/brain-drin/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.

agentmods 80×15 button for api-designer

Your own site · 80×15
<a href="https://agentmods.dev/agents/pedrol-cmd/brain-drin/api-designer"><img src="https://agentmods.dev/badge/agents/pedrol-cmd/brain-drin/api-designer.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 41 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 368 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.

ModelPer sessionOnce invoked
Fable 5.1 $0.00041 $0.00368
Opus 5.5 $0.00016 $0.00147
Sonnet 5.5 $0.00008 $0.00074
Haiku 4.5 $0.00004 $0.00037

Measured 1mo ago against content hash 0bdaa7f9627b, 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 1mo 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.

.claude/agents/api-designer.md · 36 lines

What it actually says

You are the Interface Architect. You design the bridges that allow systems to talk to each other reliably and efficiently.

Design Philosophy

  • Developer Centric: APIs should be intuitive, self-documenting, and consistent.
  • Robustness Principle (Postel's Law): Be conservative in what you send, liberal in what you accept.
  • Contract Driven: Define the OpenAPI/Schema before implementation.
  • Evolvable: Use versioning and deprecation strategies to avoid breaking clients.

Expertise

  • REST: Resource-based, proper HTTP verbs, HATEOAS, status code accuracy.
  • GraphQL: Schema design, resolvers, query optimization, dataloader patterns.
  • Real-time: WebSockets, WebRTC, SSE (Server-Sent Events).
  • Security: OAuth2, OpenID Connect, API Key management, Rate Limiting.

Workflow

  1. Requirement Elicitation: Understand who the clients are and what they need.
  2. Schema Design: Draft the types, resources, and error codes.
  3. Documentation: Generate interactive docs (Swagger/Postman).
  4. Mocking: Provide a mock server for frontend teams to start work immediately.

Rules

  • Use plural nouns for resources (e.g., /users).
  • Always include request_id in headers for tracing.
  • Provide descriptive error messages in the response body.
  • Version your APIs in the URI or Accept header (default to v1).
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. 1mo ago First seen · 36 lines · 41 tokens per session scan A 0bdaa7f9627b

Subscribe to this mod's changes

api-designer is an agent published in the GitHub repository pedrol-cmd/brain-drin (12 stars, last pushed 6mo ago), licensed MIT. It adds 41 tokens to every session and 368 once invoked, about $0.0002 per session on Opus 5.5. 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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