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    Claude CodeClaude CodeCursorCursorCodex CLICodex CLIGitHub CopilotGitHub CopilotGemini CLIGemini CLI+20 more

    API Contract Designer

    2

    Generic AI prompts often produce brittle, inconsistent APIs that lack cohesive naming or proper error handling.

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    API Contract Designer

    API Contract Designer

    Example session with this skill installed

    Design the REST API contract for a clinic booking app with patients, practitioners, appointments and availability slots. It will be used by an iOS app and a React web client.

    • Read your context and instructions
    • Compiled the api contract designer
    • Generated the UI component

    REST contract for the clinic booking API: four resources, one error format, cursor pagination and URL versioning.

    Resource model

    ResourceKey fieldsRelations
    patientsid, name, email, phonehas many appointments
    practitionersid, name, specialtyhas many slots
    slotsid, practitioner_id, starts_at, ends_at, statusat most one appointment
    appointmentsid, patient_id, slot_id, statusbelongs to patient, slot

    Conventions

    • Plural, lowercase, kebab-case paths; snake_case JSON fields
    • Timestamps in ISO 8601 UTC
    • Booking: POST /v1/appointments with slot_id; cancelling: PATCH status to cancelled

    Error format

    { "error": { "code": "slot_unavailable",
  "message": "This slot is already booked.",
  "details": [{ "field": "slot_id" }] } }

    Pagination and versioning

    Cursor based: ?limit=50&cursor=..., response has next_cursor. Version in the path (/v1); breaking changes go to /v2.

    OpenAPI skeleton

    openapi: 3.1.0
info: { title: Clinic Booking API, version: 1.0.0 }
paths:
  /v1/slots:
    get:
      parameters:
        - { name: practitioner_id, in: query }
        - { name: from, in: query }
  /v1/appointments:
    post:
      responses: { "201": {}, "409": {} }

    Next steps

    • Confirm who can see which patient data
    • Fill in schemas for each resource

    api-contract-designer.tsx

    TSX · React component

    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

    Model complex resource relationships and lifecycles before implementationGenerate consistent OpenAPI skeletons with standardized error envelopesAudit existing API designs for idempotency and retry safetyStandardize naming conventions and pagination across multiple servicesDesign robust webhook and event-driven notification schemas

    About this skill

    What it does

    The API Contract Designer is a specialized architect for your AI agent that ensures your APIs are consistent, scalable, and developer-friendly before a single line of code is written. It shifts focus from "endpoints" to "resource modeling," helping you define the nouns, relationships, and lifecycles of your domain. It handles the heavy lifting of cross-cutting concerns like idempotency, error envelopes, and pagination strategies.

    Why use this skill

    Generic AI prompts often produce brittle, inconsistent APIs that lack cohesive naming or proper error handling. This skill enforces "consistency by construction" by forcing high-level design decisions—such as auth patterns and versioning strategies—across the entire contract. It proactively flags non-idempotent operations and designs retry logic to prevent distributed systems failures.

    Supported Standards & Outputs

    • REST and GraphQL architectural styles
    • OpenAPI Spec (OAS) skeleton generation
    • Resource lifecycle modeling and relationship mapping
    • Webhook and event-driven architecture design
    • Standardized error envelopes and pagination (Cursor/Offset)

    The output is a production-ready blueprint, ranging from structured audit reports to copy-paste OpenAPI templates tailored to your specific tech stack and team constraints.

    How to install

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

    ~30 seconds
    1. 1

      Download the ZIP

      Free skills download straight away. Paid skills unlock right after purchase.

    2. 2

      Unzip into your skills folder

      Every agent reads skills from one folder on your machine. Drop the unzipped folder in there.

    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.

    Skills folder by agent

    Click the path to copy it. Create the folder if it does not exist yet.

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    4 installs

    Downloaded by developers to date

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    Security scanned

    Verified clean 3 months ago

    • Passed all security checks, Safe to install

    Listed3 months ago
    Updated11 days ago

    What's inside

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