Free Developer Tools Online
JSON, XML, and HTML formatters and validators; regex tester; code beautifiers and minifiers; encoders, and a live HTML/CSS/JS code editor. Built for the small tasks that interrupt your real work.
12 free tools — browser-based, no sign-up required.
Code Beautifier
Format and beautify your code
CSS/JS Minifier
Minify CSS and JavaScript code
JSON Formatter
Format and validate JSON data
XML Validator
Validate and format XML documents
Markdown Editor
Write and preview Markdown in real-time
Live Code Editor
Edit HTML/CSS/JS with live preview
Responsive Tester
Test website responsiveness
CSS Gradient Generator
Create beautiful CSS gradients
Regex Tester
Test and debug regular expressions
HTML Beautifier
Format and beautify HTML code
CSS Minifier
Minify and beautify CSS code
XML Formatter
Format and validate XML documents
About FlexyPdf Developer Tools
Most developer tasks that interrupt your flow are tiny: format a JSON response so you can read it, check whether a regular expression matches the cases you care about, decode a JWT to see what claims it carries, minify a CSS file before deploying. The developer tools here are designed for exactly those interruptions — fast to load, opinion-free about how you do your work, and pasteable from clipboard with a single keyboard shortcut.
The JSON formatter validates as you type, highlights the exact character where parsing fails (with a helpful message rather than a generic "unexpected token"), and supports both pretty-printing and minification. It also handles JSON5 input and JSONC (JSON with comments), which most validators reject. The regex tester runs in JavaScript regex mode but also exposes a PCRE-compatible mode for patterns copied out of grep, sed, or PHP code. Match groups are highlighted in the input text in real time.
For code formatting, the HTML and CSS beautifiers preserve your existing structure and only reformat whitespace, so the diff in git remains clean. The minifier strips comments, removes unnecessary whitespace, and where safe shortens identifiers — with a "preserve license comments" option that keeps any /*! header block intact. The live code editor renders HTML/CSS/JavaScript inline with no iframe sandbox quirks, useful for sketching a quick demo or reproducing a bug report.
Who uses these tools
A few of the recurring use cases we hear about from FlexyPdf visitors.
Backend and API developers
Formatting JSON responses, debugging payload shapes, running quick regex sanity checks against sample input.
Front-end engineers
Beautifying minified third-party CSS to read it, minifying production CSS, prototyping HTML/CSS interactions in the live editor.
DevOps and platform engineers
Validating XML configuration files, decoding/encoding Base64 secrets, sanity-checking JSON before piping it into a shell command.
Students and learners
Running small snippets of code in the browser, experimenting with regex patterns before using them in scripts.
Frequently asked questions
Do the formatters change anything other than whitespace?
No. The JSON, XML, and HTML formatters only adjust whitespace and indentation — your data, attributes, and structure are preserved byte-for-byte aside from formatting.
Is my data safe to paste into the developer tools?
Yes. All formatting, validation, and minification happens in your browser using local JavaScript. Nothing you paste is sent to a server.
Why does my regex behave differently in JavaScript and PCRE modes?
JavaScript regex (the engine browsers use natively) and PCRE (used in grep, PHP, and many other tools) have small but real differences — most notably around lookbehind support, named groups, and certain character class escapes. The tester labels the mode you are in so you can match the engine your real code will use.