Skip to content

API & HTTP Tools

Test REST APIs, debug WebSocket connections, and edit OpenAPI specs. Free online API tools for developers — all 100% browser-based. Send HTTP requests, inspect responses, test WebSocket real-time communication, and design API specifications. No backend required, everything runs in your browser.

API Tools Hub

Explore REST API client, WebSocket tester, OpenAPI editor, JWT tools, and more.

REST API Client

Send HTTP requests and view responses.

WebSocket Client

Test WebSocket connections in real-time.

OpenAPI Editor

Edit and preview OpenAPI specifications.

OpenAPI Diff

Compare two OpenAPI specs side by side.

API Mock Response Generator

Generate realistic mock JSON responses for REST API endpoints using Faker.js.

URL Encoder

URL-encode query parameters for API requests.

JWT Encoder

Create JWT tokens for API authentication.

What is a REST API?

Learn REST API principles, methods, and best practices.

What is WebSocket?

Learn how WebSocket enables real-time communication.

What is GraphQL?

Learn GraphQL queries, mutations, subscriptions, and schema design.

What is OpenAPI?

Learn OpenAPI specification structure, paths, schemas, and documentation.

How to Fix CORS Errors

Learn how to fix CORS errors with headers, preflight requests, and server config.

How to Use cURL

Complete guide to using cURL for API testing and HTTP requests.

Related Tool Categories

Explore other tool categories you might find useful:

Encoding & Decoding ToolsSecurity & Token ToolsJSON ToolsYAML Tools

Related Tools

Try these complementary developer tools:

JSON Tools Hub

Formatters, converters, and validators for JSON.

Code Generation Hub

Generate code in many languages from your data.

API Tools

REST, OpenAPI, JWT, and WebSocket utilities.

Linux Tools

Command builders and Linux utilities.

AI Prompt Engineering

Tools for crafting and testing AI prompts.

Explore Our Toolset

AI Prompt Generator

Create dynamic and reusable AI prompts with ease.

LLM Token Counter

Count tokens for GPT-4, Claude, Gemini and more — 100% client-side.

OpenAPI Editor

Design, edit, and validate OpenAPI 3.x specifications with real-time validation and beautiful docs preview. YAML/JSON support with live preview.

OpenAPI Diff

Compare two OpenAPI 3.x specifications side by side. Detect added, removed, and changed endpoints, schemas, parameters, and responses — all browser-based.

Regex Tester

Test and debug regular expressions instantly with live match highlighting and flag support.

VS Code Snippet Generator

Create, preview, validate, and export VS Code snippets without writing JSON. Visual builder with placeholders, variables, collections, and one-click export.

JSON to Code Generator

Convert JSON into clean, strongly-typed code in multiple programming languages. Generate models, classes, and structs instantly from JSON.

XML to Code Generator

Convert XML into clean, strongly-typed code across multiple languages. Supports attributes, namespaces, and complex XML schemas.

YAML to Code Generator

Convert YAML into clean, strongly-typed code for multiple languages. Supports nested schemas, anchors, and configuration files.

JSON Formatter

Make your JSON sparkle with clean, readable formatting.

JSON Editor

Edit JSON with interactive tree view and Monaco code editor.

JSON To YAML

Switch your JSON to human-friendly YAML on the fly.

JSON Schema GUI Builder

Visually build, edit, and manage JSON Schema with an intuitive GUI — no manual schema writing needed.

JSON To TOML

Convert your JSON to clean, readable TOML config format instantly.

SchemaCode ER Diagram Generator

Generate and visualize ER diagrams from SQL schemas using SchemaCode.

Mermaid Sequence Diagram Editor

Create and edit Mermaid sequence diagrams with live preview and SVG export.

Connection String Builder

Generate, parse, and convert connection strings for 14+ databases. Output to URI, JDBC, Prisma, Docker Compose, and more.

XML Editor

Edit XML with interactive tree view and CodeMirror code editor.

XML To JSON

Convert complex XML to friendly JSON in seconds.

YAML Editor

Edit YAML with interactive tree view and CodeMirror code editor.

YAML To JSON

Convert readable YAML into structured JSON effortlessly.

TOML Editor

Edit TOML with interactive tree view and CodeMirror code editor.

Base 64 Converter

Switch between base64 and other formats with ease.

Base 64 to Image

Generate and download images from base64 text

Image to Base 64

Convert images (PNG, JPEG, GIF, SVG, WebP) to Base64 strings and data URIs

Timestamp Converter

Timestamp Converter: Effortlessly convert UNIX time to human-readable format and back.

Cron Helper

Cron Helper: Build, validate, and understand crontab expressions visually with live previews and next-run insights.

Age Calculator

Age Calculator: Quickly calculate your age in years, months, and days from your date of birth.

JWT Encoder

JWT creation made simple — sign, encode, go

JWT Decoder

Decode JWTs safely — fast, clean, and offline

UUID v1 Generator

Generate UUID v1: time-based unique identifiers for distributed systems.

UUID v3 Generator

Generate UUID v3: name-based UUIDs using MD5 hashing.

UUID v4 Generator

Generate UUID v4: random UUIDs for general-purpose unique IDs.

UUID v5 Generator

Generate UUID v5: name-based UUIDs using SHA-1 hashing.

UUID v7 Generator

Generate UUID v7: time-ordered, sortable UUIDs ideal for databases.

GUID Generator

Generate GUIDs: Microsoft-style UUIDs compatible across platforms.

ULID Generator

Generate ULIDs: lexicographically sortable unique IDs for modern apps.

URL Encoder

Encode URLs to URL-safe format instantly.

URL Decoder

Decode URL-encoded strings back to plain text.

JSON URL Encoder

Encode JSON objects to URL-safe strings.

JSON URL Decoder

Decode URL-encoded strings back to JSON.

XML URL Encoder

Encode XML to URL-safe strings.

XML URL Decoder

Decode URL-encoded strings back to XML.

YAML URL Encoder

Encode YAML to URL-safe strings.

YAML URL Decoder

Decode URL-encoded strings back to YAML.

Sort Lines

Sort lines of text alphabetically or numerically.

Remove Duplicates

Remove duplicate lines from text instantly.

Word Counter

Count the number of words in your text.

Character Counter

Count the number of characters in your text.

Line Counter

Count the number of lines in your text.

Duplicate Counter

Count duplicate lines in your text.

Spaces to Newlines

Convert spaces to newlines or vice versa.

Sort Words

Sort words in your text alphabetically.

String Case Converter

Convert strings between camelCase, PascalCase, snake_case, kebab-case, and more.

HTML Entity Encoder

Encode special characters to HTML entities instantly. Perfect for escaping HTML, XML, and XSS prevention.

HTML Entity Decoder

Decode HTML entities back to readable text. Convert & < > and other entities to characters.

CSS to TailwindCSS Converter

Convert CSS declarations into TailwindCSS utility classes instantly. Supports colors, spacing, typography, layout, and responsive breakpoints.

CSP Header Generator

Build, analyze, and generate Content Security Policy headers. Supports all CSP Level 3 directives with real-time output for Nginx, Apache, Express, Next.js, and more.