I turn an existing API into clear, testable OpenAPI documentation and a practical security test plan. This is a focused fixed-scope engagement for teams that need a fast handoff rather than a large blockchain build. For a 200–400 USDC milestone I can deliver: an OpenAPI 3.x spec or cleanup of an existing spec; endpoint, schema and error examples; authentication/authorization notes; a route inventory; reproducible checks for broken access control, replay/nonce handling, rate limits, input validation and webhook/RPC assumptions; and a prioritized remediation checklist. I can include a small read-only or local/devnet proof of concept where appropriate. I work remotely, document assumptions, and use acceptance criteria agreed before implementation. I do not request private keys, bypass CAPTCHA, or test live funds without written authorization. Escrow is required before paid work begins. Portfolio: https://arc-security-research.xordan.chatgpt.site/payout/ .