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    API Breaking-Change Detector

    5

    Compare two OpenAPI specs and catch every breaking change before your consumers do — with a client migration table.

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    API Breaking-Change Detector

    API Breaking-Change Detector

    Example session with this skill installed

    Compare the attached v1.yaml and v2.json specs. Tell me what will break for our mobile app users and what I should put in the release notes.

    • Read your context and instructions
    • Compiled the api breaking-change detector
    • Generated the document

    API Change Report — User Care API 1.2.0 → 2.0.0

    Verdict: BREAKING — 2 breaking, 1 risky, 0 deprecations, 1 safe
    Semver recommendation: MAJOR — removal of login fields

    Migration table

    #SeverityEndpoint & locationWhat changedWhat consumers must do
    B1BREAKINGPOST /login -> responses.200.tokenfield removeduse access_token from response body
    B2BREAKINGGET /profileauth changedAPI Key moved from query to Header X-API-KEY

    Changelog draft

    • Moved authentication key from query parameters to headers for /profile.
    • Renamed token field to access_token in login response.

    api-breaking-change-detector.pdf

    PDF · document

    Generated

    Example file from a real run - the skill writes it into your workspace.

    Connects securely to your tools. The creator never sees your data.

    What you get

    Automate SemVer versioning decisions based on contract changesGenerate migration tables for client developers during API upgradesCatch accidental deletions of response fields in large OpenAPI filesVerify if a new optional parameter causes naming collisions for existing clients

    About this skill

    Shipping an API update without knowing what breaks is how you lose integrators. This skill compares two versions of your OpenAPI 3.x or Swagger 2.0 spec (JSON or YAML) and reports every change that matters — from the consumer's point of view.

    What it detects (10 categories):

    1. Removed & renamed paths, operations, parameters, response fields
    2. Required-ness changes — the optional-to-required trap
    3. Type & format changes, tightened constraints
    4. Enum changes — including response enums that break exhaustive switches
    5. Response shape — removed fields, changed status codes, content-type switches
    6. Auth & security — new scopes, moved API keys, changed schemes
    7. Pagination & defaults — silent behavior changes
    8. Deprecations & sunsets
    9. Additive changes verified as truly safe (collision check included)
    10. Server & base-path changes

    Every finding gets a severity — BREAKING / RISKY / DEPRECATION / SAFE — cites the exact spec location (JSON path) with old and new values, and states which side breaks: request writers or response readers.

    You get:

    • A verdict and a semver recommendation (MAJOR / MINOR / PATCH) with the reason
    • A migration table your consumers can act on directly
    • A changelog draft ready to paste into release notes
    • A "not breaking (so no one panics)" section

    RISKY is a first-class category here: new response enum values, changed defaults, new error codes. A naive diff calls these safe. Your integrators' error dashboards disagree.

    Static analysis only — it never calls your API and never fetches URLs referenced by the spec.

    Documentation & FAQ: https://43sunsets.com/go/s2-doc-01/

    Not affiliated with the OpenAPI Initiative or SmartBear Software. "OpenAPI" and "Swagger" are used only to describe compatibility.

    How to install

    Works the same in every agent - Claude, Cursor, Codex, Copilot and 20+ more.

    ~30 seconds
    1. 1

      Download the ZIP

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    2. 2

      Unzip into your skills folder

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    3. 3

      Ask your agent to use it

      Restart the agent if it was already running. It picks the skill up automatically - no config needed.

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    Security scanned

    Verified clean 2 months ago

    • Passed all security checks, Safe to install

    Listed2 months ago
    Updated1 month ago

    What's inside

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