api-designer

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

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 agents/ashtonian/llm-init/api-designer
Clone the repo
git clone --depth 1 https://github.com/ashtonian/llm-init

Made for: Claude Code.

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. 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 $0.00029 $0.01504
Opus 5 $0.00015 $0.00752
Sonnet 5 $0.00006 $0.00301
Haiku 4.5 $0.00003 $0.00150

Measured yesterday against content hash a4f76bee0f9a, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, 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 yesterday.

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. yesterday 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 6mo ago), licensed MIT. It adds 29 tokens to every session and 1,504 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 2026-08-31.

Related

Other agents, from other repositories

Demonstrate

Agent for demonstrating VS Code features.

microsoft/vscode · 10 tokens

playwright-test-generator

Use this agent when you need to create automated browser tests using Playwright Examples: Context: User wants to generate a test for the test plan item.

microsoft/playwright · 151 tokens

.NET-Notebook-Migration-Agent

Expert .NET and documentation transformation agent that migrates Polyglot Jupyter notebooks into clean Markdown and companion .NET sample code.

microsoft/ai-agents-for-beginners · 33 tokens

AVM Owner Triage

Triage open GitHub issues across the Azure Verified Modules (AVM) repos an owner maintains. Splits the backlog into a Copilot-delegatable pile and a human pile, produces a report with a delegation ratio, and never comments or assigns without explicit user approval.

github/awesome-copilot · 61 tokens

Ultimate Transparent Thinking Beast Mode

Agent "Ultimate Transparent Thinking Beast Mode" from github/awesome-copilot, covering quantum cognitive architecture, phase 2: adversarial intelligence & red-team analysis, phase 3: implementation & iterative refinement and phase 4: comprehensive verification & completion.

github/awesome-copilot · 11 tokens

code-reviewer

Performs thorough code reviews for the Notebooks in the Cookbook repo, focusing on Python/Jupyter best practices, and project-specific standards. Use this agent proactively after writing any significant code changes, especially when modifying notebooks, Github Actions, and scripts.

anthropics/claude-cookbooks · 52 tokens