Format, encode, convert and debug — faster.
A complete toolkit for engineers: JSON formatters, encoders, hash generators, JWT decoders and more. Everything runs locally in your browser, so your data never leaves your device.
Popular Developer tools
JSON Formatter & Validator
Beautify, minify and validate JSON with clear error reporting.
Base64 Encode / Decode
Convert text and files to and from Base64 in one click.
URL Encode / Decode
Percent-encode and decode URLs and query parameters.
UUID Generator
Generate cryptographically random UUID v4 identifiers.
Regex Tester
Test regular expressions live with match highlighting and capture groups.
Cron Expression Generator
Build, explain and preview cron schedules in plain English.
Unix Timestamp Converter
Convert Unix timestamps to human dates and back, in local and UTC time.
Hash Generator
Compute SHA-1, SHA-256, SHA-384 and SHA-512 hashes.
JSON to CSV Converter
Convert between JSON arrays and CSV with proper quoting and parsing.
CSV to JSON Converter
Convert CSV to JSON with headers, delimiter detection and no upload.
SQL Formatter
Format and beautify SQL for MySQL, PostgreSQL, SQLite and more.
JWT Decoder
Decode and inspect JSON Web Token headers and payloads.
HTML Entity Encode/Decode
Encode and decode HTML entities, including numeric and named references.
Markdown Previewer
Write Markdown and see rendered output plus clean HTML, live.
Color Contrast Checker
Check WCAG color contrast ratios with AA and AAA pass/fail results.
YAML ↔ JSON Converter
Convert YAML to JSON and JSON to YAML, privately in your browser.
CSS Minifier & Beautifier
Minify CSS to shrink files, or beautify minified CSS to read it.
Number Base Converter
Convert numbers between binary, octal, decimal and hexadecimal.
XML Formatter & Validator
Beautify, minify, validate XML and convert it to JSON.
Chmod Calculator
Convert Linux file permissions between checkboxes, octal and symbolic.
JSON Escape / Unescape
Escape text for JSON strings, or unescape JSON back to plain text.
Newest
CSV to JSON Converter
Convert CSV to JSON with headers, delimiter detection and no upload.
YAML ↔ JSON Converter
Convert YAML to JSON and JSON to YAML, privately in your browser.
XML Formatter & Validator
Beautify, minify, validate XML and convert it to JSON.
JSON Escape / Unescape
Escape text for JSON strings, or unescape JSON back to plain text.
Learn about Developer
Understanding JSON: A Practical Guide for Developers
What JSON is, how it is structured, and the common mistakes that break parsers — with examples you can fix in seconds.
What Is Base64? How Encoding Works and Common Mistakes
What Base64 encoding actually does, where it is used, and the mistakes that cause broken or oversized output.
encodeURI vs encodeURIComponent: Which One to Use
How percent-encoding works, the difference between encoding a whole URL and a single component, and the mistakes that break links.
What Is a UUID? Version 4 vs Version 7 Explained
What a UUID looks like, why version 4 is the safe default, when version 7 is better, and best practices for IDs.
How SHA-256 and SHA-512 Hashes Work: Hashing vs Encryption
What a hash function does, how to choose between SHA-256 and SHA-512, and why hashing is not encryption.
What Is a JWT? Header, Payload and Signature Explained
A JSON Web Token has three parts. Learn what the header, payload and signature contain, how to read the claims, and why decoding is not verifying.
What Is HTML Encoding? Entities & Escaping Explained
Learn how HTML encoding works, why escaping prevents XSS and layout breaks, and how to encode and decode named, decimal, and hex entities.
Unix Time Explained: Seconds, Milliseconds and Time Zones
What a Unix timestamp is, how to tell seconds from milliseconds, how time zones come into it, and the values worth recognising.
Binary, Octal, Decimal and Hex: How Number Bases Work
How positional number bases work, why very large values need exact arithmetic, and the hex and binary values you meet every day.
Regex Basics: How Patterns, Flags and Character Classes Work
How a regular expression is built, what the flags change, and the character classes you will use most.
How to Convert JSON to CSV: Quoting and Nested Data
How JSON maps to CSV rows and columns, why correct quoting matters, and how to flatten nested data without losing it.
WCAG Color Contrast Explained: AA and AAA Ratios
What the WCAG contrast ratio measures, the 4.5:1 and 7:1 thresholds for AA and AAA, and how the rules change for large text and interface components.
Cron Every 5 Minutes — and the Rest of Cron Syntax, Explained
The five fields of a cron expression, the */5 pattern everyone searches for, and the day-of-week gotcha that surprises even experienced engineers.
Cron Expression Cheat Sheet — Copy-Paste Schedule Examples
Free cron expression cheat sheet with copy-paste examples for every 5 minutes, hourly, daily at midnight, weekdays only, and more.
Cron Every 10 Minutes — Syntax, Examples and Best Practices
Use the cron expression */10 * * * * to run jobs every 10 minutes, plus examples for common schedules and troubleshooting tips.
Why CSV Is Tricky to Parse: Delimiters, Quotes and Headers
Why CSV files are harder to read correctly than they look, how to choose the right JSON shape, and the mistakes to avoid.
YAML vs JSON: Differences That Matter When Converting
Why YAML is not just indented JSON, the types the two formats disagree on, and best practices for converting config files.
XML Formatting and Common XML Errors Explained
Why raw XML is hard to read, the errors that break sitemaps and feeds, when to minify, and how XML compares with JSON.
JSON String Escaping: What Needs Escaping and When
Which characters must be escaped inside a JSON string, when you need to do it, and how it differs from URL encoding.
Markdown Basics and Common Formatting Pitfalls
The Markdown syntax you will use most, the formatting mistakes that break a document, and the GitHub extras that change the output.
Why Minify CSS? What Is Safe to Remove and What Can Break
What CSS minification removes, when it is worth doing, which shortcuts are safe, and what a simple minifier can break.
Cron Every Hour, Day & Midnight: All Daily Schedules
Master standard daily cron schedules: cron every hour, every day at midnight, twice a day, and custom hourly intervals with copy-paste examples.
URL Encoding Explained: %20 vs +, Reserved Characters & Rules
Complete guide to percent encoding in URLs: learn when to use %20 vs +, how reserved characters like & and ? work, and how to avoid encoding bugs.
Percent Encoding Reference Table (Every Character)
Complete percent encoding ASCII reference table: quick lookup for spaces, slashes, ampersands, punctuation, and UTF-8 special characters in URLs.
CSS Border Radius: 15 Copy-Paste Examples
15 modern CSS border radius examples: rounded cards, pills, circle avatars, asymmetrical organic blobs, and fancy 8-value border radius shapes.
Free Developer Tools Online: 2026 Developer Toolkit & Guides
Explore 30+ free browser-based developer tools: JSON formatters, Base64 converters, cron generators, regex testers, SQL formatters, and hash generators.
Developer FAQ
Yes — every tool is free with no account required.
Most tools run entirely in your browser, so once the page loads they keep working without sending your data anywhere.