Open-Source CLI Tool for Instant API Mocking

Innovation Idea · Intermediate · JavaScript, API Design

Problem Statement

Frontend developers lose days waiting for backend APIs. Existing mocking tools are GUI-focused, require accounts, or have complex setups. There is no zero-configuration CLI tool that turns an OpenAPI spec into a working mock server.

Proposed Solution

Build a CLI tool that takes an OpenAPI/Swagger spec and immediately starts a local mock server with realistic, schema-aware data. One command, zero configuration.

Key Features

• One-command startup — mock-server api-spec.yaml
• OpenAPI 3.x support — Full schema and response type support
• Realistic data generation — Schema-aware, not random
• Response delay simulation — Realistic latency
• Error simulation — Configurable error responses
• Request logging — All incoming requests
• CORS enabled — Works with frontend dev
• TypeScript types — Generate interfaces from spec

Implementation Approach

Phase 1: Core Engine (4-6 weeks)

Node.js CLI with Commander.js. OpenAPI 3.x parsing. Schema-to-mock-data generator. Express server.

Phase 2: Advanced Features (4-6 weeks)

Delay simulation, error injection, request logging, custom overrides, TypeScript generation.

Phase 3: Polish & Community (4-6 weeks)

npm publish, documentation, OpenAPI 2.x support, proxy fallback.

Technology Stack

• Node.js / TypeScript — Runtime and CLI
• swagger-parser — OpenAPI parsing
• Express — Mock server
• Faker.js — Realistic data generation

FAQ

What makes this different from Prism (Stoplight)?

Prism focuses on validation and has a complex setup. This tool prioritizes zero-configuration instant startup.