Markdown Tools
Tool · New
18 free Markdown tools that run in your browser: an editor, slides, a README generator, Markdown to PDF, Word, Slack and Jira, a linter and more.
New
Developer
Regex Tester
Write a pattern, paste your test text, and see every match highlighted as you type, with numbered and named groups listed underneath. Add a replacement to preview the result.
Loading Regex Tester…
Runs on your device. Nothing you paste is uploaded.
How to use the Regex Tester
- Type the pattern without slashes, and choose flags such as g (all matches) or i (ignore case).
- Paste the text to test against. Matches are highlighted and listed with their groups and positions.
- Optionally type a replacement, using $1 or $<name> for groups, and copy the replaced text.
Private by design
Plenty of online tools send what you paste to their server, which is a real risk with API keys, tokens and customer data. Regex Tester runs entirely in your browser: nothing is uploaded, logged or stored, and it keeps working with your network switched off. It’s free, with no account and no limits.
Questions
Which regex flavour does this use?
JavaScript’s, as in your browser, Node.js and Deno. It’s close to PCRE, Python and Java for most patterns, including lookbehind and named groups, but some features such as possessive quantifiers and recursion aren’t available.
What does the u flag do?
It treats the pattern and text as Unicode, so . matches a whole emoji and \p{L} matches any letter in any language. The v flag adds set operations on top.
Why did it stop with a timeout?
Some patterns, like (a+)+$, take exponentially longer as the text grows. The tester runs your pattern separately from the page and stops it after two seconds so the tab never freezes; rewrite the nested repetition to fix it.
Is anything I paste sent to a server?
No. Every tool runs in your browser, so tokens, keys, customer data and code stay on your device. Once the page has loaded, the tools work offline too.
Do I need an account?
No. Every developer tool is free to use without signing in, with no limits.
Related tools
- Diff Checker Compare two texts and see every added, removed and changed line.
- Cron Expression Generator Build or read a cron schedule in plain English, with its next run times.
- URL Encode and Decode Percent-encode text for URLs, decode it, and split a URL into parts.
- JSON Formatter Pretty-print, minify and validate JSON, with the line of any error.
Part of Developer Tools
16 free developer tools that run in your browser: format JSON, decode JWTs, test regex, compare text and encode Base64 without sending anything to a server.
More tools
See allLabel Maker
Tool · New
Print labels from Excel, Google Sheets or a CSV file: pick an Avery-compatible sheet, skip used labels and download a PDF. Addresses, QR codes and barcodes.
Printable Planners & Trackers
Tool · New
14 free printable planners and trackers: weekly and monthly plans, routines, meals, chores, budgets, workouts and more. Edit and print in your browser.