I Built a Claude Code Skill That Reverse-Engineers Undocumented APIs
I Built a Claude Code Skill That Reverse-Engineers Undocumented APIs Because "the docs are in the code" is not a documentation strategy. The Week I Lost to Grepping I joined a new team last month. Day 1 task: add a feature to the billing service. Day 1 reality: I opened the API docs and realized they were from 2022. Half the routes had been rewritten. The other half never had docs to begin with. So I did what every backend dev does. I grepped. grep -r "app.get|app.post|router." src/ --include="*.js" Four hours later, I had a notebook full of endpoints, a headache, and zero confidence that I had found everything. I found routes that worked but were not documented. I found docs for routes that did not exist anymore. I found one GET /invoices/:id endpoint with zero auth checks that had been sitting there since 2022. This is normal. And it should not be. The Idea What if I could drop a single file into a repo and have Claude Code map the entire API layer for me? Not from annotations. Not from existing OpenAPI specs. From the actual code. So I built it. Meet API Archaeologist API Archaeologist is a Claude Code / Codex CLI skill that reads your source code and reverse-engineers your API layer. It finds: • Internal endpoints — REST, GraphQL, gRPC, WebSockets • External integrations — third-party APIs, webhooks, SDK clients • Auth flows — JWT, OAuth, API keys, session cookies, RBAC • Security gaps — unauthenticated routes, hardcoded secrets, missing rate limits • Dead code — auth middleware with no endpoints, orphaned routes And it generates two things: API_DISCOVERY.md — A complete catalog with Mermaid diagrams openapi-draft.yaml — A draft OpenAPI spec How It Works The skill is just a SKILL.md file. Claude Code reads it and follows the instructions. It: Discovers route definitions Traces handlers, DTOs, middleware, services, and database calls Maps authentication and authorization Finds external API calls and integrations Flags potential security and reliability risks Gene