API Contract Reviewer

API Contract Reviewer is an agent for Claude Code from srnichols/plan-forge. It costs 31 tokens per session (1,234 once invoked), scanned A, original, MIT.

A reviewer for HTTP API contracts, the agreed shape and behavior of an API used by clients. It checks compatibility, versioning, OpenAPI documentation, pagination, rate limits, and standardized error responses.

In plain words
What is it for?
Use it to audit REST endpoints, request and response fields, versioning plans, filtering and sorting, throttling, and RFC 9457 Problem Details errors.
Why use it?
It helps prevent API changes from breaking existing clients and reveals inconsistent or incomplete endpoint behavior.

Agent for Claude Code

Written for Claude Code: a Claude Code subagent (agents/*.md).

Good fit Use it to audit REST endpoints, request and response fields, versioning plans…

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Install with agentmods
npx agentmods add agents/srnichols/plan-forge/api-contract-reviewer
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/srnichols/plan-forge

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 Contract Reviewer

README.md
[![agentmods](https://agentmods.dev/badge/agents/srnichols/plan-forge/api-contract-reviewer.svg)](https://agentmods.dev/agents/srnichols/plan-forge/api-contract-reviewer)
Your own site
<a href="https://agentmods.dev/agents/srnichols/plan-forge/api-contract-reviewer"><img src="https://agentmods.dev/badge/agents/srnichols/plan-forge/api-contract-reviewer.svg" alt="Measured on agentmods" height="20"></a>
Per session 31 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 1,234 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 $0.00031 $0.01234
Opus 5 $0.00015 $0.00617
Sonnet 5 $0.00006 $0.00247
Haiku 4.5 $0.00003 $0.00123

Measured 3d ago against content hash a227cb9a88bb, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-06, from the pricing page.

Security

Grade A, and why

API Contract Reviewer 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 3d 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.

presets/shared/.github/agents/api-contract-reviewer.agent.md · 132 lines

How it starts

The opening of the file, as written. The whole thing — 132 lines — stays where its author put it; the contents beside it link to each section on GitHub.

You are the API Contract Reviewer. Audit API surface area for contract stability, consistency, and SaaS-readiness.

Your Expertise

  • RESTful API design and backward compatibility
  • OpenAPI / Swagger specification correctness
  • Pagination, filtering, and sorting conventions
  • Rate limiting and throttling patterns
  • Error response standards (RFC 9457 Problem Details)
  • API versioning strategies (URL path, header, query string)

Standards

  • RFC 9457 — Problem Details for HTTP APIs (error response format)
  • OpenAPI 3.x Specification — API documentation and contract validation
  • ISO 8601 — date/time format in request/response payloads
  • Semantic Versioning — API version lifecycle (breaking vs non-breaking)

API Contract Review Checklist

Backward Compatibility

  • No removed or renamed fields in existing response models
  • No changed field types (e.g., stringint) without versioning
  • No removed endpoints — deprecate first, remove in next major version
  • New required request fields have defaults or are added via a new version
  • Enum values only added, never removed or renamed

Versioning

  • API version specified in route or header (/api/v1/, api-version header)
  • Breaking changes only in new major versions
  • Deprecated endpoints marked with Deprecated attribute/annotation/decorator
  • Version documented in OpenAPI spec

Request/Response Conventions

  • Consistent naming (camelCase or snake_case — not mixed)
  • Dates in ISO 8601 format (2026-03-23T14:30:00Z)
  • IDs are strings or UUIDs (not sequential integers exposed externally)
  • Nullable fields explicitly documented

Pagination

  • Collection endpoints support pagination (limit/offset or cursor-based)
  • Default page size reasonable (10–50, not unbounded)
  • Response includes total count or next-page cursor
  • Maximum page size enforced server-side

Error Responses

  • All errors return structured Problem Details (RFC 9457)
  • HTTP status codes semantically correct (400 vs 422 vs 409)
  • Error responses include type, title, status, detail
  • Validation errors list individual field failures
  • No stack traces or internal details in production errors

Read the full file on GitHub · 132 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. 3d ago First seen · 132 lines · 31 tokens per session scan A a227cb9a88bb

Subscribe to this mod's changes

API Contract Reviewer is an agent published in the GitHub repository srnichols/plan-forge (5 stars, last pushed 4d ago), licensed MIT. It adds 31 tokens to every session and 1,234 once invoked, about $0.0002 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 2026-09-03.

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