Free tools for developers
Design & Build
9 toolsAPI Designer
Describe an API and get a working OpenAPI 3.1 spec back.
Understand your API
Paste a spec, get a plain-English explanation.
OpenAPI Editor and Visualizer
Design, lint, visualize, and preview OpenAPI specs.
OpenAPI validator
Validate a spec, score its design, and autofix what it can.
cURL to code
Paste a curl command and get it in your language of choice.
JSON to types
Paste JSON and get TypeScript, Python, or Go types.
Mock from OpenAPI spec
Paste a spec, mock every endpoint at once.
Instant mock API
Pick a resource, get a live mock endpoint.
Editable mock API
Paste JSON or text, get an editable endpoint.
Test & Validate
18 toolsREST API Client
Test REST, SOAP, SSE, and other HTTP-based APIs.
GraphQL Client
Create and run GraphQL queries and mutations.
WebSocket Client
Connect to a WebSocket server and send or receive messages.
Socket.IO Client
Publish and subscribe to Socket.IO events.
gRPC Client
Invoke unary and streaming methods on a gRPC server.
MCP Client
Connect to remote MCP servers and inspect their capabilities.
API Health Check
Get latency and throughput for any API endpoint.
Website Uptime Check
See if any API, site, or service is down.
API Monitor
Schedule a real monitor for any URL and watch runs land live.
Multi-step API Monitor
Schedule a real monitor for chained requests and watch runs land live.
Website Speed Test
Get response time and TTFB for any website.
SSL Certificate Check
See when a domain's TLS certificate expires.
HTTP Header Check
See what every response header does to caching, CORS and security.
API load test
Hit any endpoint with virtual users and see latency, throughput and errors.
RPS calculator
Estimate throughput from users and think time.
Test data generator
Generate mock CSV or JSON test rows for API testing.
AI unit test generator
Paste a function and get unit tests in your framework of choice.
Webhook payload explainer
Paste a payload, learn what every field means.
Start free. Grow into the full platform.
Every tool here runs in your browser with no signup. When you're ready for the full workflow — Spec Hub, Monitors, performance testing, and the Collection Runner — create a free Postman account and pick up right where you left off.