JavaScript RegExp checks
The page evaluates patterns with JavaScript RegExp syntax, which is useful for browser code, Node.js utilities, form validation, and frontend tests.
Regex Tester
Enter a JavaScript regex pattern, toggle g/i/m/s/u/y flags, and inspect live matches, indexes, capture groups, named groups, and errors.
Use it for JavaScript regex checks, email patterns, validation rules, and parser tests.
Match highlights, indexes, capture groups, named groups, and flags stay visible together.
- Test JavaScript regex patterns
- Inspect capture group matches
- Toggle g i m s u y flags
How to use Regex Tester
Use this flow to test a JavaScript regex pattern against realistic sample text and inspect the exact matches before implementation.
- 1
Enter the pattern and sample
Paste or type the regex pattern without surrounding slashes, then add sample text that includes expected matches, edge cases, and strings that should fail.
- 2
Toggle JavaScript flags
Turn g, i, m, s, u, or y on only when the target code uses that behavior. Watch the match count and invalid-pattern feedback as flags change.
- 3
Inspect matches and groups
Read highlighted matches, indexes, numbered capture groups, and named groups. Copy the pattern only after it handles positive and negative examples correctly in tests.
Flag toggles
Turn global, case-insensitive, multiline, dotall, Unicode, and sticky flags on or off while the result updates immediately inside sample text.
Match highlighting
Matched ranges are highlighted inside the sample text, making it easier to see overmatching, missing matches, and zero-width surprises.
Capture group details
The match details list shows each match index plus numbered and named capture groups, so extraction logic can be reviewed before coding.
Invalid pattern feedback
Syntax errors appear near the pattern controls, helping you fix broken character classes, groups, escapes, and flag combinations faster.
Copyable pattern
Copy the tested regex pattern after sample text review, then paste it into the JavaScript code, validator, or documentation that needs it.
Regex Tester privacy and processing
Regex Tester explains how the pattern and sample text are evaluated, what is stored, and why browser-side testing still needs target-runtime confirmation.
Processing Browser
Regex Tester builds a JavaScript RegExp in the browser from the pattern and selected flags, then updates highlights and match details in the page.
Storage None
Regex Tester does not create a saved server copy of your pattern, sample text, matches, or capture group details during normal use.
Regex Tester account access
Regex Tester works without sign-in for pattern debugging, validation checks, parser experiments, sample text review, and quick QA passes.
Before You Use Regex Tester
Review these notes before using a tested regular expression in production validation, parsing, search, cleanup, or extraction work.
Privacy
Use representative sample text instead of real passwords, tokens, customer records, or private messages whenever possible.
If sensitive text is necessary for debugging, remove it from the page after the regex behavior has been confirmed.
Accuracy
A regex that passes one sample can still fail on longer text, Unicode input, empty strings, or unexpected punctuation.
Test both positive and negative examples, including edge cases that should not match, before copying the pattern into code.
Compatibility
This page follows JavaScript RegExp behavior, which can differ from PCRE, Python, Go, Java, database, or analytics regex engines.
Confirm support for lookbehind, Unicode behavior, sticky matching, and dotall flags in the exact runtime that will execute the pattern.
Output
Copy the pattern with the intended flags documented nearby, because missing flags can change match count and captured groups.
Re-test the pattern in the target app, test suite, or runtime before using it for blocking validation or bulk text changes.
Limits
Regex Tester evaluates JavaScript RegExp patterns against the sample text in the active browser page; very large text or expensive patterns may slow matching.
The match details panel shows the first 25 matches, so broad global patterns should still be tested in the destination code path.
It does not convert patterns between regex engines, benchmark catastrophic backtracking, or guarantee safety for every production input.
Questions about Regex Tester
Is this a JavaScript regex tester?
Yes. The page builds a JavaScript RegExp from your pattern and selected flags, then applies it to the sample text shown in the browser.
Which regex flags can I test?
You can toggle g, i, m, s, u, and y. Keep only the flags your target code uses, because flags can change matching, grouping, and index behavior.
Does Regex Tester require an account?
No. You can test patterns, edit sample text, inspect matches, and copy a regex without signing in. Remove sensitive sample text when finished.
Why does my regex behave differently elsewhere?
Regex engines differ across languages and products. Re-test important patterns in the exact JavaScript, backend, database, or analytics environment that will run them.
4.4 (343 ratings)