Test JavaScript Regex Online

Enter a pattern and flags, then see matches highlighted in real time with capture groups and indices. Built on the JavaScript RegExp engine for accurate results.

Regex Tester

LOCAL · Browser-Only

Test and debug regular expressions with live matching and highlights

Pattern

//g

Test String

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Quick Start

1Type your regex pattern in the pattern field
2Toggle flags like g, i, m, and s
3Paste your test string below
4Review highlighted matches and capture groups

What This Tool Does

Pattern, flags and test string sit across the top and the matches appear underneath. Every match is shown with its position, the exact text it matched, and its capture groups, with named groups listed separately from the numbered ones.

Five tabs share the same pattern. Matches is the default. Replace applies a substitution with clickable helpers for the dollar-sign references. Explain breaks the pattern down token by token in plain English. Code Generator emits the equivalent pattern for eight languages. Tests lets you list inputs that should and should not match and shows each one passing or failing.

All seven JavaScript flags are available, including the indices flag that reports the start and end position of every capture group. Fourteen presets come with sample text attached, so opening the email or UUID preset gives you something to match against straight away.

Limits Worth Knowing

The engine is the browser's own regular expression engine, so what you see here is what your JavaScript will do.
A pattern that runs longer than about a second and a half is stopped and reported as a likely runaway rather than freezing the page.
A check warns about nested quantifiers that can cause runaway backtracking. It is advisory and blocks nothing.
There is no split mode. Matching and replacing are the two operations.
Patterns and test strings are kept locally, so they are still there when you come back.

Common Questions

Will these results match my server code?

They match JavaScript exactly. Other engines differ on lookbehind, named group syntax and Unicode handling, which is what the code generator's per-language notes are for.

What does the d flag do?

It reports the start and end index of every capture group, not just of the whole match, which is what you need when you are slicing the original string rather than reading the captured text.

Can I check a pattern against several inputs at once?

Yes, on the tests tab. Add each input, mark whether it should match, and the tab header shows how many pass.

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Looking for FAQs and advanced options? Visit the full Regex Tester page →

What This Tool Does

Limits Worth Knowing

The engine is the browser's own regular expression engine, so what you see here is what your JavaScript will do.

A pattern that runs longer than about a second and a half is stopped and reported as a likely runaway rather than freezing the page.

A check warns about nested quantifiers that can cause runaway backtracking. It is advisory and blocks nothing.

There is no split mode. Matching and replacing are the two operations.

Patterns and test strings are kept locally, so they are still there when you come back.