Best Free Online Developer Tools (2026)

JSON Formatter & Validator

Paste messy JSON, get it formatted with proper indentation and syntax highlighting. Also validates and shows errors with line numbers. The single most-used developer tool online.

Also useful: JSON Validator, JSON Minifier, JSON Diff

JSON to YAML Converter

Bidirectional conversion between JSON and YAML. Essential for developers working with Kubernetes configs, Docker Compose files, or any YAML-based tooling.

Also useful: YAML to JSON, YAML Validator, YAML Beautifier

CSV to JSON Converter

Turn spreadsheet data into API-ready JSON. Handles headers, custom delimiters, and nested structures.

Also useful: JSON to CSV, CSV to XML

SQL Formatter

Format messy SQL queries with proper indentation, keyword uppercasing, and consistent style. Supports MySQL, PostgreSQL, and standard SQL dialects.

JavaScript Beautifier

De-minify and format JavaScript code. Also works for TypeScript. Great for reading third-party minified scripts.

Also useful: JS Minifier, TypeScript Formatter, Python Formatter

CSS Beautifier

Format compressed CSS into readable, indented code. Pair with the CSS Minifier for production builds.

Also useful: HTML Beautifier, XML Formatter

Base64 Encoder/Decoder

Encode text or files to Base64, or decode Base64 back to its original form. Used constantly for API tokens, email encoding, and data URIs.

Also useful: Base64 Image Decoder, Image to Base64

JWT Decoder

Decode JSON Web Tokens to inspect the header, payload, and expiration status. Essential for debugging authentication. Read our JWT guide for more details.

URL Encoder/Decoder

Encode special characters for use in URLs, or decode percent-encoded strings back to readable text.

Also useful: HTML Entity Encoder, Morse Code Translator

Regex Tester

Write and test regular expressions with real-time match highlighting, capture group display, and flag options. Saves hours of trial-and-error. Read our regex guide to learn the syntax.

JSONPath Tester

Query JSON data using JSONPath expressions. Test your queries against sample data before using them in code.

Also useful: XPath Tester

Hash Generator

Generate SHA-256, SHA-1, SHA-512, and MD5 hashes from any text. Useful for verifying file integrity and working with APIs that require request signing.

Password Generator

Generate cryptographically secure passwords with configurable length, character sets, and entropy display. Uses the Web Crypto API — nothing leaves your browser.

AES Encryption/Decryption

Encrypt and decrypt text using AES-256. Client-side only — your plaintext and keys are never transmitted.

UUID Generator

Generate v4 UUIDs in bulk. Configurable format options (uppercase, no hyphens). Read our UUID guide for best practices.

Crontab Generator

Build cron expressions visually instead of memorizing the syntax. Shows the next scheduled run times so you can verify your expression is correct.

Chmod Calculator

Calculate Unix file permission values visually. Toggle read/write/execute for owner/group/other and get the numeric and symbolic notation. Read our chmod guide.

QR Code Generator

Generate QR codes from any URL or text. Download as PNG for print or digital use. Read our QR code guide.

CSS Gradient Generator

Build linear and radial gradients visually, then copy the CSS. No more guessing at color stop positions.

Also useful: CSS Box Shadow Generator

Color Converter

Convert between hex, RGB, HSL, and CMYK color formats. Includes a visual color picker.

Also useful: Color Palette Generator, Hex to RGB, CMYK to RGB

Diff Checker

Compare two blocks of text side-by-side with highlighted differences. Works for code, config files, or any text. Also available as JSON Diff and Text Diff.

Markdown Preview

Write Markdown with a live rendered preview. Supports GitHub Flavored Markdown including tables, task lists, and code blocks.

Also useful: Markdown to HTML, HTML to Markdown, Markdown Table Generator

Text Case Converter

Convert between camelCase, snake_case, UPPER_CASE, Title Case, and more. Useful for adapting variable names between coding conventions.

Also useful: Word Counter, Slug Generator, Sort Lines, Remove Duplicates

IP Subnet Calculator

Calculate network addresses, broadcast addresses, host ranges, and subnet masks from CIDR notation. Essential for network configuration.

HTTP Status Code Reference

Searchable reference for all HTTP status codes with descriptions and common causes. Faster than Googling "what does 422 mean."

Gitignore Generator

Generate .gitignore files for any language or framework. Select your tech stack and get a comprehensive gitignore instantly.