API Mock & Scenario Builder

Local contract simulation

Turn OpenAPI or HAR into success, failure and latency scenarios with reusable test handlers.

0Operations

0Paths

0Scenarios

0Failure scenarios

0Latest issues

example-store.openapi.yaml

openapi: 3.1.2
info:
  title: Example Store API
  version: 1.0.0
servers:
  - url: https://api.example.test
paths:
  /products/{id}:
    get:
      summary: Get a product
      parameters:
        - name: id
          in: path
          required: true
          schema: { type: string }
          example: p_123
      responses:
        '200':
          description: Product
          content:
            application/json:
              schema:
                type: object
                required: [id, name, price]
                properties:
                  id: { type: string }
                  name: { type: string }
                  price: { type: number, minimum: 0 }
              example: { id: p_123, name: Atlas Notebook, price: 24.5 }
        '404':
          description: Not found
          content:
            application/json:
              schema:
                type: object
                required: [title, status]
                properties:
                  title: { type: string }
                  status: { type: integer }
              example: { title: Product not found, status: 404 }
  /orders:
    post:
      summary: Create an order
      requestBody:
        required: true
        content:
          application/json:
            schema:
              type: object
              required: [productId, quantity]
              properties:
                productId: { type: string }
                quantity: { type: integer, minimum: 1 }
      responses:
        '201':
          description: Created
          content:
            application/json:
              schema:
                type: object
                properties:
                  id: { type: string }
                  status: { type: string }
              example: { id: ord_456, status: pending }

How to use it

01
Import the contract
Paste OpenAPI JSON or YAML, open a HAR file, or use the complete example without contacting any captured host.
02
Design and run scenarios
Configure status, latency, response, probability and network failures, then simulate requests against the local contract.
03
Reuse the mocks
Export MSW handlers, Playwright routes, Vitest checks, a Worker example or a portable scenario manifest.

Frequently asked questions

Does this publish a hosted mock API?

No. The static page simulates locally and generates code that you run in your own development or test environment.

Will imported HAR requests be replayed?

No. Captures are parsed locally and never sent to their original hosts automatically.

Are captured credentials included in exports?

Known sensitive headers, query fields and token-shaped values are redacted before preview and generation, but you should still review every export.

Is contract validation exhaustive?

No. The simulator checks a practical local subset of request requirements and JSON Schema response structure; your production validator remains authoritative.

Keep working with other focused browser utilities.

All tools

How to use it

Import the contract

Design and run scenarios

Reuse the mocks

Frequently asked questions

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