Free Developer Tools

Everyday utilities for building and debugging software — validate JSON, decode a JWT, test a regex, diff two files, work out a subnet or look up DNS records. Every tool runs locally in your browser, so nothing you paste is ever uploaded.

• JSON Validator

  Validate and pretty-print JSON with the exact position of any syntax error — trailing commas, single quotes, bad escapes. Runs locally, nothing uploaded.

  Open JSON Validator → Guide

• Base64 Encoder / Decoder

  Encode and decode Base64 text (UTF-8 safe) and Base64-encode any file, right in your browser. Nothing is uploaded.

  Open Base64 Encoder / Decoder → Guide

• JWT Decoder

  Decode, verify and generate JSON Web Tokens in your browser. Inspect claims, verify HS/RS/ES/PS/EdDSA signatures, decrypt JWEs and sign new tokens.

  Open JWT Decoder → Guide

• Regex Tester

  Test regular expressions with live match highlighting and capture groups. Uses your browser's own regex engine — nothing is uploaded.

  Open Regex Tester → Guide

• Unix Timestamp Converter

  Convert Unix timestamps to human dates and back, with live epoch time and timezone-aware output. Runs entirely in your browser.

  Open Unix Timestamp Converter → Guide

• Time Zone Converter

  Convert any date and time between cities and time zones, DST-aware, and compare working hours to find a meeting slot. Free and browser-based.

  Open Time Zone Converter → Guide

• URL Encoder / Decoder

  Encode or decode URLs and query strings (percent-encoding), with a breakdown of any URL into host, path and decoded parameters. Free, runs in your browser.

  Open URL Encoder / Decoder → Guide

• SQL Formatter

  Format and beautify SQL queries — clause-aware indentation, keyword uppercasing, one column per line — or minify to a single line. Free, runs in your browser.

  Open SQL Formatter → Guide

• Cron Expression Parser

  Paste a cron expression to get plain English and the next 10 run times in any time zone. Presets for common schedules. Free, runs in your browser.

  Open Cron Expression Parser → Guide

• YAML Validator & Converter

  Validate YAML with line/column errors and convert YAML to JSON or JSON to YAML — Kubernetes manifests, CI configs, compose files. Free, runs in your browser.

  Open YAML Validator & Converter → Guide

• CSV ↔ JSON Converter

  Convert CSV to JSON and JSON to CSV with proper quote handling, delimiter auto-detect, header and type options, file upload and download. Runs in your browser.

  Open CSV ↔ JSON Converter → Guide

• Code Minifier & Beautifier

  Minify or beautify HTML, CSS and JavaScript in your browser — comment stripping, whitespace collapse and re-indenting, with byte savings shown. Free and local.

  Open Code Minifier & Beautifier → Guide

• XML Formatter & Converter

  Format and validate XML with strict parser errors, minify it, or convert XML to JSON and JSON to XML with the standard @attribute/#text mapping. Runs locally.

  Open XML Formatter & Converter → Guide

• HTML Entity Encoder / Decoder

  Escape HTML special characters or decode &-style entities back to text, with a searchable reference of named and numeric entities. Runs in your browser.

  Open HTML Entity Encoder / Decoder → Guide

• PX ↔ REM Converter

  Convert px to rem and rem to px instantly. Set any root font size, see a table of common values, and copy ready-to-paste CSS. Free, no sign-up.

  Open PX ↔ REM Converter → Guide

• Web Framework Finder

  Answer a few questions — language, rendering, what you're building — and get a ranked shortlist of web frameworks with stars and notable users.

  Open Web Framework Finder → Guide

• .gitignore Generator

  Compose a .gitignore for your OS, editor, language and framework in seconds — Node, Python, Go, Rust, Terraform and more. Copy or download, in-browser.

  Open .gitignore Generator → Guide

• JSON to TypeScript / Zod / Pydantic Converter

  Paste JSON and get TypeScript interfaces, Zod schemas, Pydantic models or Go structs — nested types named, optional fields detected. Runs locally.

  Open JSON to TypeScript / Zod / Pydantic Converter → Guide

• Chmod Calculator

  Convert Linux file permissions between checkboxes, octal (755, 644) and rwx notation — with setuid/setgid/sticky bits and plain-English explanations.

  Open Chmod Calculator → Guide

• HTTP Status Code Reference

  Every HTTP status code explained in practical terms — 1xx to 5xx plus the nginx and Cloudflare codes (499, 522) you meet in real logs. Works offline.

  Open HTTP Status Code Reference → Guide

• UUID Generator

  Generate random UUID v4 identifiers in bulk, with uppercase and no-dashes options and one-click copy. Uses your browser's secure RNG — nothing is uploaded.

  Open UUID Generator → Guide

• Color Picker & Converter

  Pick a colour and convert between HEX, RGB and HSL, with a built-in WCAG contrast checker. Runs entirely in your browser.

  Open Color Picker & Converter → Guide

• CSS Gradient Generator

  Create linear and radial CSS gradients visually: pick colours and stops, set the angle, preview live, and copy the CSS. Runs entirely in your browser.

  Open CSS Gradient Generator → Guide

• Number Base Converter

  Convert numbers between binary, octal, decimal, hexadecimal and any base from 2 to 36. Arbitrary-precision, updates live, runs entirely in your browser.

  Open Number Base Converter → Guide

• Subnet & CIDR Calculator

  Get the network and broadcast address, usable host range, netmask, wildcard mask and host count for any IPv4 CIDR block — and split it into subnets.

  Open Subnet & CIDR Calculator → Guide

• DNS Lookup

  Look up a domain's DNS records — A, AAAA, MX, TXT, NS, CNAME, CAA and SOA — live from your browser over DNS-over-HTTPS, each explained in plain English.

  Open DNS Lookup → Guide

Other categories

• Security & Crypto Tools
• Finance & Business Tools
• Gaming Tools
• Text Tools
• Calculators & Converters
• Media & File Tools
• AI & LLM Tools
• All tools →