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    API Contract Breaking Change Reviewer

    1

    Automated API contract reviewer for detecting breaking changes in OpenAPI, GraphQL, and Protobuf specifications.

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    API Contract Breaking Change Reviewer

    API Contract Breaking Change Reviewer

    Example session with this skill installed

    Review this diff for an OpenAPI spec. We changed 'user_id' from an optional string to a required integer and added a new optional 'timezone' field. Current version is v1.2.0.

    • Read your context and instructions
    • Compiled the api contract breaking

    The review identified one confirmed breaking change and one non-breaking additive change. The shift in data type and requirement status for the primary identifier will break all existing consumers.

    API Compatibility Review: v1.2.0 Update

    Executive Compatibility Verdict

    Verdict: BLOCK RELEASE
    Compatibility Score: 45/100 (High Risk)

    ChangeCompatibilitySeverityConfidenceConsumer ImpactAction
    user_id: string (opt) -> int (req)BREAKINGCriticalHighExisting clients sending strings or omitting field will receive 400 Bad Request.Revert to optional or use a new field name.
    timezone: added optional stringNON-BREAKINGInfoHighNo impact on existing consumers; provides new functionality.None required.

    Versioning Assessment

    • Recommended Version: MAJOR (v2.0.0)
    • Reason: Confirmed breaking change to a core request parameter (user_id).
    • Breaking Changes: Type mismatch and requirement tightening.

    Required Migration: Consumers must update logic to cast identifiers to integers and ensure the field is present in all payloads.

    Recommended Migration Strategy

    1. Additive Transition: Keep user_id as an optional string. Introduce user_id_int as an optional integer.
    2. Deprecation Phase: Mark user_id as deprecated in documentation and headers.
    3. Telemetry: Monitor logs to identify consumers still sending string values.
    4. Cutover: Once string traffic hits <1%, enforce the integer requirement in a new major version.

    Next steps

    • Revert the user_id requirement tightening to maintain v1.x compatibility.
    • Implement a temporary compatibility layer to handle both string and integer inputs.
    • Update the API documentation to reflect the timezone addition.

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    About this skill

    API Contract & Breaking Change Reviewer

    Catch breaking API changes before they reach your users.

    API changes can look harmless in a diff and still break clients, SDKs, integrations, and downstream services.

    API Contract & Breaking Change Reviewer analyzes API specifications, schema changes, endpoint modifications, and supplied code diffs to identify compatibility risks before release.

    What it does Detects confirmed and potential breaking changes Reviews OpenAPI / Swagger, JSON Schema and GraphQL Analyzes gRPC & Protocol Buffers compatibility Checks request, response, endpoint, schema, and behavioral changes Evaluates consumer impact and migration risk Calculates a structured Compatibility Score (0–100) when sufficient evidence is available Makes an evidence-based Semantic Versioning recommendation Determines whether the change belongs in PATCH, MINOR, or MAJOR Builds a practical deprecation and migration timeline Creates a structured Risk Register Recommends concrete compatibility fixes Produces a clear release decision From API Diff to Release Decision

    API Change → Contract Analysis → Breaking Change Detection → Consumer Impact → Compatibility Score → SemVer Decision → Migration Strategy → Release Gate

    Instead of simply telling you that an API changed, the reviewer answers the questions that actually matter:

    Will this break existing consumers? How serious is the risk? Should this be a PATCH, MINOR, or MAJOR release? What needs to change before release?

    Built for developers and engineering teams

    Useful for

    Backend engineers API developers Platform teams API architects Engineering leads Teams reviewing pull requests Organizations maintaining public or internal APIs Evidence-first analysis

    The reviewer does not invent consumers, production usage, traffic levels, compatibility guarantees, incidents, or migration completion.

    Findings are separated into confirmed, inferred, not evidenced, and conflicting information, with severity and confidence assessed independently.

    Supported review modes Full Contract Review Breaking Change Review Request / Response Review Endpoint Review Schema Review PR / Diff Review Release Gate Review Final output

    Get a structured compatibility report containing

    Breaking Changes → Consumer Impact → Compatibility Score → Semantic Versioning → Deprecation Timeline → Migration Strategy → Risk Register → Release Decision

    Stop discovering breaking API changes after deployment. Review the contract before you ship.

    Find more skills like this on the Claude Skills Marketplace, the Codex Skills Marketplace and the Gemini Skills Marketplace, or browse Claude Skills for APIs & Backend.

    Cannot predict production behavior for undocumented consumer patterns. Requires explicit old and new schemas for delta analysis. Cannot verify runtime logic not present in the contract.

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    What's inside

    Frequently Asked Questions

    This skill identifies breaking changes in API specifications (OpenAPI, GraphQL, Protobuf) by analyzing diffs to determine if modifications—like removing fields or changing data types—will crash existing client integrations or SDKs.

    The reviewer supports OpenAPI (Swagger), JSON Schema, GraphQL, and gRPC/Protocol Buffers, making it versatile for RESTful, event-driven, and microservice architectures.

    It is designed to be compatible with leading AI agents and development environments that support file uploads or text-based code analysis, easily integrating into your existing CI/CD or PR review workflows.

    You receive a structured report that includes a Compatibility Score, a Semantic Versioning recommendation (Major, Minor, or Patch), a risk register, and a suggested migration timeline for affected consumers.

    Unlike basic diff tools, this skill performs an evidence-first analysis of behavioral changes and consumer impact, distinguishing between confirmed breaking changes and low-risk modifications.

    New in APIs & Backend