API Contract Testing Skill for AI Agents: Validate OpenAPI 3.x

API Contract Testing Skill for AI Agents: Validate OpenAPI 3.x

This skill validates an API contract against an OpenAPI 3.x specification, either in JSON or YAML format, and an optional manifest of expected endpoints. It ensures the API adheres to the spec it claims to fulfill.

What this skill does

• Enumerates operations from the OpenAPI spec, including paths and webhooks.
• Checks internal consistency of the spec for unresolved references, duplicates, and missing responses.
• Compares a manifest of expected endpoints against the spec offline.
• In live mode, probes each endpoint from the manifest over HTTP, comparing actual status with the expected one.
• Generates a machine-readable JSON report outlining endpoints count, missing endpoints from the spec, contract violations, conformances, and errors.
• Utilizes exit codes 0/1/2 for integration into automated workflows.

Who it is for

This skill is designed for developers and engineering teams employing AI coding agents like Claude Code, Cursor, and Codex, who need to verify API specifications against actual implementations.

Use cases

• Validating in-house API development to ensure adherence to original specifications.
• Performing regular checks during the development lifecycle to catch discrepancies early.
• Integrating into CI/CD pipelines to automate API compliance checks pre-deployment.

Technical details

This skill is developed using pure Python 3 standard library tools (argparse, json, pathlib, sys, urllib.request). It includes a minimal built-in YAML subset parser and does not rely on external libraries such as PyYAML or requests. The skill seamlessly interfaces with related tools such as `api-doc-generator` and `test-generator`, closing the loop for complete API documentation and testing workflows.

For authorised security testing, defensive research, and educational use only.

Source & Licence

This package is built on open-source work published by bestdeejay-design (bestdeejay-design/agent-skills) and distributed under MIT. The original licence text and copyright notice are included in your download.

Personal and commercial use, modification and redistribution are permitted, provided the original copyright and licence notice are retained.

Your purchase covers curation, licence verification, packaging, documentation and instant delivery. It does not grant exclusive rights to the underlying open-source code, which remains available under its original licence.

Delivery & Support

• Delivery: instant — a secure download link is emailed to you as soon as payment is confirmed.
• Format: ZIP archive containing the skill files, documentation and the original licence.
• Support: support@mcpcart.com — we aim to reply within 2 business days.
• Updates: updates are included only where stated on this page.

Refunds

This is a digital product delivered immediately after purchase. By completing your order you request immediate delivery and acknowledge that, once the download has been accessed, the statutory right to cancel no longer applies to the extent permitted by law. Refund requests are handled in accordance with our published Refund Policy.

Claude, Codex, Gemini and Cursor are trademarks of their respective owners. MCP Cart is an independent marketplace and is not affiliated with, endorsed by, or sponsored by any of them. Compatibility references describe interoperability only.