Best API & HTTP Tools
A hand-checked list of the best free api & http tools for developers. Every tool runs in your browser — no upload, no login, no API key.
16 tools
API Contract Analyzer
API & HTTP
Lint an OpenAPI or Swagger spec for contract quality issues.
API Breaking Change Detector
API & HTTP
Diff two OpenAPI specs and flag breaking changes.
API Consistency Auditor
API & HTTP
Audit an API for naming, casing and response consistency.
API Response Schema Generator
API & HTTP
Turn a JSON API response into OpenAPI, JSON Schema or TypeScript.
API Changelog Generator
API & HTTP
Generate a Markdown changelog from two OpenAPI versions.
Postman ↔ OpenAPI Converter
API & HTTP
Convert a Postman collection to OpenAPI 3 and back again.
OpenAPI / Swagger Validator
API & HTTP
Validate OpenAPI 3.x / Swagger 2.0 documents in JSON or YAML.
WebSocket Frame Explainer
API & HTTP
Decode WebSocket frame bytes into opcode, flags, mask and payload.
HAR File Analyzer
API & HTTP
Analyse a HAR export: slow requests, errors, sizes and host breakdowns.
HTTP Request Builder
API & HTTP
Send live API requests and generate curl, fetch, axios snippets.
cURL to Fetch Converter
API & HTTP
Convert a curl command into JavaScript fetch() code.
GraphQL Query Formatter
API & HTTP
Format and indent GraphQL queries and mutations.
cURL Command Parser & Code Generator
API & HTTP
Convert a curl command to fetch, Axios, Python, Go, PHP, Java, C#, Rust or Dart code.
Webhook Request Inspector
API & HTTP
Inspect a pasted webhook request and verify its HMAC signature.
GraphQL Schema Viewer
API & HTTP
Browse a GraphQL SDL schema's types, queries, and mutations.
WebSocket Tester
API & HTTP
Open a live WebSocket connection, send frames and read replies.