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    API Mock Server

    1

    Zero-dependency Python mock server that generates validating APIs from OpenAPI/Swagger specs with latency simulation.

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    API Mock Server

    API Mock Server

    Example session with this skill installed

    Spin up a mock server for my petstore.yaml spec. I need it to simulate a slow connection with a 500ms delay and handle a 10% failure rate for testing my frontend's error boundaries.

    • Read your context and instructions
    • Compiled the api mock server

    I have configured and started the API mock server using your petstore.yaml specification. The server is now listening for traffic with simulated latency and error rates enabled.

    Mock Server Deployment

    
# Starting the server with 500ms latency and 10% error rate
python3 scripts/mock_server.py petstore.yaml --port 4010 --latency 500 --error-rate 0.1

# Server Output Log:
# [INFO] Loading petstore.yaml...
# [INFO] Found 8 operations.
# [INFO] Base path: /v1
# [INFO] Mock server running at http://localhost:4010
# [DEBUG] GET /v1/pets - 200 OK (500ms delay)
# [DEBUG] POST /v1/pets - 400 Bad Request (Missing required field: name)
# [DEBUG] GET /v1/pets/123 - 500 Internal Server Error (Simulated)

    Next steps

    Test Error Handling: Point your frontend to http://localhost:4010 and observe how the UI reacts to the 10% simulated failure rate.

    Force Responses: Use the Prefer: code=404 header in your requests to test how your application handles specific documented error states.

    Verify Schema: Submit a malformed JSON body to a POST endpoint to confirm the server correctly catches and logs validation errors.

    and started the API mock server using your petstore.yaml

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

    About this skill

    Frontend and mobile development often stall when the backend isn't ready or the staging environment is down. This skill provides a zero-dependency Python mock server that instantly turns any OpenAPI 3 or Swagger 2 specification into a functional, validating local API.

    What it does

    • Spec-driven mocking parses your OpenAPI/Swagger YAML or JSON to serve all defined endpoints.
    • Data generation produces realistic responses based on schemas, respecting types, enums, formats, and required fields.
    • Request validation checks incoming path/query parameters and JSON bodies, returning 400 or 422 errors for schema violations.
    • Resilience testing simulates network conditions using configurable latency ranges and error rates.
    • Dynamic control allows users to force specific status codes or named examples via standard headers.

    How it works

    1. Load the mock server by providing your OpenAPI file path to the script.
    2. Configure the runtime with flags for port, latency, error probability, or randomness.
    3. Request endpoints using a browser, cURL, or your application code to receive schema-compliant responses.
    4. Monitor the request log in the terminal to debug incoming traffic and validation failures.

    Frameworks & tools

    This tool is built for Python 3 environments and works with any OpenAPI 3.0 or Swagger 2.0 specification. It supports CORS for integration with React, Vue, and other browser-based frameworks.

    Why this beats prompting it yourself

    Writing individual mock routes is repetitive and error-prone. This skill automates the entire contract-to-mock pipeline, ensuring your frontend tests against the actual schema definitions rather than hallucinated payloads.

    Use cases

    • Frontend prototyping when the backend API is still under design or development.
    • Resilience testing to see how your app handles 500 errors or high-latency responses.
    • Demo environments for showing off UI features without needing a live database or auth.
    • Offline development to keep working on features while traveling or during outages.

    Known limitations

    Requires Python 3 installed on the host machine. Does not support complex authentication logic or stateful data persistence between restarts.

    How to use

    Skills on Agensi run inside your AI agent. Copy the prompt, paste it into your agent, and it connects to Agensi and installs this skill for you. If a payment is needed, your agent shows it to you first.

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