Free Online Developer Tools

A growing collection of lightweight, browser-based utilities built for JavaScript and web developers. Every tool runs entirely client-side - your data never leaves your browser. No sign-up, no API calls, no tracking.

Data & JSON Tools

JSON Formatter & Validator

Paste raw JSON to validate, prettify, or minify it instantly. Syntax errors are highlighted with line numbers.

Data

CSV to JSON Converter

Convert CSV data into a JSON array of objects using the first row as keys.

Data

JSON to CSV Converter

Turn a JSON array of objects into downloadable CSV with automatic header detection.

Data

JSON to TypeScript Interface

Generate TypeScript interfaces from JSON data, including nested objects and arrays.

Data

JWT Decoder

Decode JSON Web Token headers and payloads without verification. Inspect claims and expiry dates.

Data

String & Encoding Tools

Base64 Encode / Decode

Encode plain text to Base64 or decode Base64 strings back to readable text.

Encoding

URL Encode / Decode

Safely encode and decode URL components using JavaScript's built-in methods.

Encoding

HTML Escape / Unescape

Convert special characters to HTML entities and back. Prevent XSS and display raw HTML safely.

String

Slug Generator

Turn any title or sentence into a clean, URL-safe slug for routing and SEO.

String

Case Converter

Convert text between camelCase, PascalCase, snake_case, kebab-case, and CONSTANT_CASE.

String

Query String Builder & Parser

Build URL query strings from key-value pairs or parse existing query strings into structured output.

String

Code Tools

JavaScript Beautifier & Minifier

Beautify messy JavaScript for readability or minify clean code for production.

Code

Regex Tester

Test regular expressions against sample text. View matches, captured groups, and replacement previews in real time.

Code

Diff Checker

Compare two blocks of text and see line-by-line additions, removals, and unchanged lines.

Code

JavaScript Tools

Event Loop Visualiser

Interactive visual model of the JavaScript event loop. Step through the call stack, microtask queue, and macrotask queue.

JavaScript

Promise to Async/Await Converter

Convert Promise chains with .then() and .catch() into clean async/await syntax.

JavaScript

JavaScript Equality Checker

Compare two values with ==, ===, and Object.is(). See how type coercion affects loose equality.

JavaScript

Truthy / Falsy Checker

Enter any JavaScript value to find out whether it is truthy or falsy and understand why.

JavaScript

Array Method Finder

Describe what you want to do with an array and get the right method with syntax and examples.

JavaScript

Date & Schedule Tools

Unix Timestamp Converter

Convert between Unix timestamps (seconds & milliseconds) and human-readable dates in UTC and local time.

Date

Cron Expression Parser

Paste a 5-part cron expression and get a plain-English description of when it runs.

Schedule

Cron Expression Builder

Use simple dropdowns and controls to build a cron expression without memorising the syntax.

Schedule

Utility Tools

UUID Generator & Validator

Generate RFC 4122 v4 UUIDs instantly or validate whether a string is a valid UUID.

Utility

CSS Colour Converter

Convert colours between HEX, RGB, RGBA, HSL, and HSLA with a live preview swatch.

Utility

Number Base Converter

Convert numbers between binary, octal, decimal, and hexadecimal with input validation.

Utility

Why Use These Tools?

Every tool on this page is built with plain HTML, CSS, and vanilla JavaScript. There are no server-side calls - your data is processed entirely in your browser and never transmitted anywhere. That makes these tools fast, private, and available offline once loaded.

Whether you're debugging a JSON payload at 2 AM, decoding a JWT from a colleague, or quickly generating a UUID for a database seed, these tools are designed to get out of your way and give you the answer instantly.