Regex Tester
Live regex matcher with capture group inspection
Paste a pattern and a test string, see matches highlighted in real time. Capture groups, flags, replacement preview — all in your browser.
Vendor 27ABCDE1234F1Z5 has been verified. Buyer GSTIN 29XYZAB5678Q1Z3 is active.
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What is a Regex Tester?
Regular expressions are the most powerful and least readable tool in any developer's belt. A working regex looks like glyphs from a forgotten alphabet — and the moment you tweak one character, half the matches disappear. The only way to write a regex with confidence is to test it against real data, see what matches, and inspect each capture group.
This tester runs the JavaScript RegExp engine — the same one used by Node.js, your browser, and most modern tools. Edit the pattern or test string and matches highlight live, with each capture group laid out in a separate panel so you can verify exactly what each `(...)` is grabbing.
Use it to draft regexes for log parsing, GSTIN extraction, URL validation, scraping — anywhere you need a string-matching rule that you can later paste into JS, Python, or your IDE's find-and-replace.
Why use this Regex Tester
Built for Indians, by Indians. Every number, every formula, every slab — tuned to FY 2026-27 reality.
Live highlighting
Matches are highlighted in the test string as you type the pattern.
Capture group breakdown
Each match shows its index plus the value of every capture group.
All standard flags
Toggle g, i, m, s, u flags — see how each affects matching.
Syntax errors inline
Invalid patterns show the JS engine's error directly so you can fix the issue.
No submit button
Updates instantly as you edit — keeps your flow tight.
100% browser-side
Patterns and test strings never leave your machine.
Using the Regex Tester in 4 steps
No onboarding, no signup. Answer three fields and the numbers update live.
Enter a pattern
Type or paste your regex pattern (without the surrounding slashes).
Pick flags
Toggle g (global), i (case-insensitive), m (multiline), s (dotAll), u (unicode).
Paste a test string
Drop sample data into the test pane — log lines, JSON, prose, anything.
Verify each match
Use the highlighted output and the capture-group panel to confirm the pattern catches what you expect.
Tips to get the most out of it
Always start with a small, anchored pattern and grow outward — `^foo$` first, then add quantifiers and alternations.
Test edge cases: empty string, leading/trailing whitespace, mixed case. Most regex bugs ship to prod because someone tested only the happy path.
Use named capture groups (`(?<year>\d{4})`) for anything you will read 6 months from now — `match.groups.year` is way clearer than `match[1]`.
Be wary of catastrophic backtracking — patterns like `(a+)+` can hang on adversarial input. Prefer atomic groups or non-greedy quantifiers in user-facing code.
Real-world scenarios
How Indians actually use this tester — concrete inputs, concrete outcomes.
GSTIN extraction
Pattern `\b\d{2}[A-Z]{5}\d{4}[A-Z][A-Z0-9]Z[A-Z0-9]\b` against a paragraph of vendor invoices — instantly highlights every valid GSTIN. Confirmed before pasting into a backend script.
Log timestamp parser
Pattern `(\d{4}-\d{2}-\d{2})T(\d{2}:\d{2}:\d{2})` against an Nginx log dump. Capture groups separate date and time, ready to drop into a JS date constructor.
Indian phone numbers
Pattern `(?:\+91[\s-]?)?[6-9]\d{9}` against a contact list. Matches both with and without country code, validates the Indian mobile prefix.
Frequently Asked Questions
Still have a question? Our team replies within a business day.
JavaScript RegExp — the same engine in Node.js and modern browsers. If you need to test PCRE (Python, PHP, Perl) regex, the syntax is mostly compatible but lookbehinds and some character classes differ.
`\K` is PCRE-only and not supported in JavaScript. Use a lookbehind `(?<=...)` instead.
Paste your multi-line text in the test pane and toggle the m flag — `^` and `$` then match start/end of each line, not the whole string.
You can use the pattern, but always also test against adversarial input — long inputs, unicode edge cases, malformed encodings. Catastrophic backtracking is a real DoS vector.
Not in this version — the focus is on match inspection. Use your IDE or a Node REPL for replace previews.
No. Reload the page and the input clears. Nothing is sent to a server.
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