api-designer

api-designer is an agent for Claude Code from ashtonian/llm-init. It costs 29 tokens per session (1,504 once invoked), scanned A, original, MIT.

An agent focused on designing and implementing API contracts for REST, gRPC, and GraphQL services. An API contract defines how software systems exchange requests and responses.

In plain words
What is it for?
Use it to design OpenAPI specifications, inspect existing routes, and implement versioned, multi-tenant API services.
Why use it?
It provides a consistent process for planning endpoints, documentation, authentication, and tenant isolation before implementation.

Agent for Claude Code

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

Good fit Use it to design OpenAPI specifications, inspect existing routes, and implement versioned, multi-tenant API services.

Compare 6 agents from other repositories ↓
Install with agentmods
npx agentmods add agents/ashtonian/llm-init/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/ashtonian/llm-init

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/ashtonian/llm-init/api-designer/github.svg)](https://agentmods.dev/agents/ashtonian/llm-init/api-designer)
Your own site
<a href="https://agentmods.dev/agents/ashtonian/llm-init/api-designer"><img src="https://agentmods.dev/badge/agents/ashtonian/llm-init/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/ashtonian/llm-init/api-designer"><img src="https://agentmods.dev/badge/agents/ashtonian/llm-init/api-designer.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 29 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 1,504 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 $0.00029 $0.01504
Opus 5.5 $0.00012 $0.00602
Sonnet 5.5 $0.00006 $0.00301
Haiku 4.5 $0.00003 $0.00150

Measured 1mo ago against content hash a4f76bee0f9a, 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.

templates/.claude/agents/api-designer.md · 117 lines

How it starts

The opening of the file, as written. The whole thing — 117 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Your Role: API Designer

You are an api-designer agent. Your focus is designing and implementing API contracts that are consistent, well-documented, and multi-tenant aware.

Startup Protocol

  1. Read context:

    • Read .claude/rules/api-design.md for REST conventions and standards
    • Read .claude/rules/auth-patterns.md for authentication and authorization patterns
    • Read .claude/rules/multi-tenancy.md for tenant context and isolation requirements
    • Read existing API specs/routes to understand established patterns
  2. Inventory existing APIs: Scan **/handler*, **/route*, **/api/** to understand existing URL structure, naming conventions, and middleware stack before adding new endpoints.

Priorities

  1. Contract first -- Design the API contract (OpenAPI spec) BEFORE writing any implementation code. The spec is the source of truth. Implementation derives from it, not the other way around.
  2. Consistency -- Every endpoint follows the same conventions for URL structure, pagination, filtering, error responses, and headers. No snowflake endpoints.
  3. Multi-tenant safety -- Tenant context is ALWAYS extracted from the JWT, never from URL parameters. Every data access is scoped to the authenticated tenant.
  4. Backward compatibility -- Never break existing consumers. Additive changes only within a version. Use versioning for breaking changes.

RESTful Design Conventions

  • URL structure: /api/v1/{resource} (plural nouns). Nested for relationships: /api/v1/orgs/{orgId}/members.
  • HTTP methods: GET (read, idempotent), POST (create), PUT (full replace), PATCH (partial update), DELETE (remove).
  • Status codes: 200 (OK), 201 (Created with Location header), 204 (No Content for DELETE), 400 (Bad Request), 401 (Unauthenticated), 403 (Forbidden), 404 (Not Found), 409 (Conflict), 422 (Validation Error), 429 (Rate Limited), 500 (Internal Error).
  • Response envelope: { "data": {...}, "meta": {...} } for single items, { "data": [...], "meta": { "cursor": "...", "has_more": true } } for lists.

Read the full file on GitHub · 117 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.

  1. 1mo ago First seen · 117 lines · 29 tokens per session scan A a4f76bee0f9a

Subscribe to this mod's changes

api-designer is an agent published in the GitHub repository ashtonian/llm-init (2 stars, last pushed today), licensed MIT. It adds 29 tokens to every session and 1,504 once invoked, about $0.0001 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 2026-08-31.

Related

Other agents, from other repositories

php-developer

Write idiomatic PHP code with design patterns, SOLID principles, and modern best practices. Implements PSR standards, dependency injection, and comprehensive testing. Use PROACTIVELY for PHP architecture, refactoring, or implementing design patterns.

davepoon/buildwithclaude · 51 tokens

backend-reviewer

Use when reviewing service-layer logic, module boundaries, business rules, or cross-service contracts — verifies architecture integrity and service correctness against the api and architect persona standards.

jeremylongshore/tons-of-skills-marketplace · 36 tokens

integrations-engineer

Third-party integration specialist for SMB Product-Builder archetypes. Owns the integration contract — OAuth2/API-key flows, webhook signature verification, idempotency keys, retry/backoff with jitter, rate-limit handling, secret storage, and sandbox→prod promotion — for Stripe, Twilio, QuickBooks, Google/Microsoft…

avelikiy/great_cto · 106 tokens

gate

API quality gates — linting, style enforcement, breaking change CI, and API governance.

tonone-ai/tonone · 19 tokens

broadcasting-agent

Creates WebSocket broadcasting infrastructure (NestJS backend) and real-time consumption on the frontend (Next.js or React). Use when adding real-time event broadcasting to a bounded context, creating Socket.IO gateways, or implementing frontend event listeners. Dispatched after infrastructure layer is complete.

Softtor/nestjs-hexagonal · 58 tokens

dotnet-architecture-reviewer

Reviews a .NET codebase or repository and produces a structured architecture report — layering and dependency-rule violations, coupling, CQRS/handler hygiene, EF Core boundary leaks, testability, and concrete prioritized fixes. Use when the user wants an architecture review, a "second opinion" on structure, a PR-level…

StefanTheCode/dotnet-ai-toolkit · 102 tokens