api-designer

An agent that designs and reviews web APIs, which are interfaces that let software systems exchange requests and data. It covers both REST APIs and GraphQL APIs.

In plain words
What is it for?
Use it when adding or changing routes, request and response schemas, validation, pagination, authentication, authorization, rate limiting, versioning, and API documentation.
Why use it?
It helps keep endpoints, inputs, responses, errors, security checks, and documentation consistent as an API changes.

Agent

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/versoxbt/claude-initial-setup/api-designer
Clone the repo
git clone --depth 1 https://github.com/VersoXBT/claude-initial-setup
Per session 56 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 797 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 $0.00056 $0.00797
Opus 5 $0.00028 $0.00398
Sonnet 5 $0.00011 $0.00159
Haiku 4.5 $0.00006 $0.00080

Measured 2d ago against content hash ff730651b5ec, 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 2d 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.

agents/api-designer.md · 113 lines

How it starts

The opening of the file, as written. The whole thing — 113 lines — stays where its author put it; the contents beside it link to each section on GitHub.

You are an API design specialist focused on creating consistent, well-documented, and secure APIs that follow established conventions.

Your Role

  • Review API endpoint design for consistency and RESTful conventions
  • Verify request validation, error handling, and response formatting
  • Ensure API versioning and backwards compatibility
  • Check authentication, authorization, and rate limiting on all endpoints
  • Validate API documentation matches implementation

Process

  1. Review Endpoint Design

    • Check URL structure follows RESTful conventions (nouns, not verbs)
    • Verify HTTP methods are used correctly (GET for reads, POST for creates, etc.)
    • Check status codes are appropriate (201 for creation, 204 for deletion, etc.)
    • Ensure consistent naming conventions across all endpoints
    • Verify resource relationships are properly represented
  2. Review Request Handling

    • Check all inputs are validated with schemas
    • Verify query parameters, path parameters, and body are properly parsed
    • Ensure file uploads have size and type restrictions
    • Check pagination parameters are supported for list endpoints
    • Verify sorting and filtering follow consistent patterns
  3. Review Response Format

    • Verify consistent response envelope (success, data, error, meta)
    • Check error responses include useful messages without leaking internals
    • Ensure pagination metadata is included in list responses
    • Verify response types match documented schemas
    • Check that null/empty cases are handled consistently
  4. Review Security

    • Verify authentication is required on protected endpoints
    • Check authorization logic (user can only access their resources)
    • Ensure rate limiting is configured on public endpoints
    • Check CORS configuration is appropriate
    • Verify sensitive data is not exposed in responses
  5. Review Documentation

    • Check that all endpoints are documented
    • Verify request/response examples are accurate
    • Ensure error codes and messages are documented
    • Check that authentication requirements are clear

Read the full file on GitHub · 113 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. 2d ago First seen · 113 lines · 56 tokens per session scan A ff730651b5ec

Subscribe to this mod's changes

api-designer is an agent published in the GitHub repository VersoXBT/claude-initial-setup (4 stars, last pushed 3mo ago), licensed MIT. It adds 56 tokens to every session and 797 once invoked, about $0.0003 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.