Regex Tester

Test JavaScript regular expressions with capture groups and flags.

Edit the pattern, flags, and test string. Matches and capture groups update live. Replacement preview is included so you can sanity-check String.prototype.replace before shipping.

Pattern

Flags

Test string

Matches

[0] index 12: hello@infoz.com
groups: ($1: hello) ($2: infoz.com)
[1] index 31: partners@example.org
groups: ($1: partners) ($2: example.org)

About this tool

Compiles your pattern with the browser's RegExp constructor. Flags supported: g (global), i (case-insensitive), m (multiline), s (dotAll), u (unicode), y (sticky). Errors from RegExp construction are surfaced inline. Capture groups (numbered + named) are listed below the match for quick verification.

When to use this

Authoring a regex you'll embed in JavaScript or TypeScript code — the engine here is identical to what your code will run.
Validating user-input patterns (email, postal code, ID format) before pushing to production.
Reverse-engineering an existing regex by removing pieces and watching what stops matching.
Sanity-checking a String.replace() rewrite against a corpus of test inputs without spinning up a REPL.

Frequently asked questions

Which regex flavor does this support?: JavaScript / ECMAScript only. The pattern is compiled with the browser's native RegExp constructor, so anything that runs in modern V8/SpiderMonkey/JavaScriptCore works — including lookbehinds, named groups, and Unicode property escapes (\p{Letter}). Patterns from PCRE, Perl, Python, or .NET that rely on those engines' extensions (recursion, balanced groups, possessive quantifiers, conditionals) won't parse here — translate them first.
What are the flags doing?: g (global): find every match, not just the first. i (case-insensitive): A matches a. m (multiline): ^ and $ anchor at every line break, not just at the start/end of input. s (dotAll): . matches newlines. u (unicode): treats the pattern as a sequence of Unicode code points and enables \p{} property escapes. y (sticky): match starting only at lastIndex, no skipping ahead.
Why does my pattern run forever or hang the browser?: Catastrophic backtracking — usually from nested quantifiers like (a+)+ against a long mismatching string. The browser's RegExp engine doesn't time out, so this tool can hang the tab if you write one. Test with a short input first; if a 100-char string takes more than a second, your pattern needs rewriting (often as a possessive quantifier or atomic group, neither of which JavaScript supports — so you may need to restructure entirely).
Does this support replace mode?: Yes. The replacement field uses standard String.prototype.replace semantics: $1, $2, ... refer to capture groups, $<name> for named groups, $& for the whole match, $$ for a literal dollar. Without the g flag only the first match is replaced.
Anything sent to a server?: No. Pattern, flags, test input, and replacement string all run via the browser's RegExp + String APIs. Nothing leaves your device — useful when testing patterns against snippets of customer data, log lines, or PII you don't want to upload to a third-party service.

Related tools

All processing happens entirely in your browser — no input is sent to our servers. Page reviewed and maintained by the infoz editorial desk; report bugs or request features via /contact.

About this tool

When to use this

Authoring a regex you'll embed in JavaScript or TypeScript code — the engine here is identical to what your code will run.

Validating user-input patterns (email, postal code, ID format) before pushing to production.

Reverse-engineering an existing regex by removing pieces and watching what stops matching.

Sanity-checking a String.replace() rewrite against a corpus of test inputs without spinning up a REPL.

Frequently asked questions

Which regex flavor does this support?

JavaScript / ECMAScript only. The pattern is compiled with the browser's native RegExp constructor, so anything that runs in modern V8/SpiderMonkey/JavaScriptCore works — including lookbehinds, named groups, and Unicode property escapes (\p{Letter}). Patterns from PCRE, Perl, Python, or .NET that rely on those engines' extensions (recursion, balanced groups, possessive quantifiers, conditionals) won't parse here — translate them first.

What are the flags doing?

g (global): find every match, not just the first. i (case-insensitive): A matches a. m (multiline): ^ and $ anchor at every line break, not just at the start/end of input. s (dotAll): . matches newlines. u (unicode): treats the pattern as a sequence of Unicode code points and enables \p{} property escapes. y (sticky): match starting only at lastIndex, no skipping ahead.

Why does my pattern run forever or hang the browser?

Catastrophic backtracking — usually from nested quantifiers like (a+)+ against a long mismatching string. The browser's RegExp engine doesn't time out, so this tool can hang the tab if you write one. Test with a short input first; if a 100-char string takes more than a second, your pattern needs rewriting (often as a possessive quantifier or atomic group, neither of which JavaScript supports — so you may need to restructure entirely).

Does this support replace mode?

Yes. The replacement field uses standard String.prototype.replace semantics: $1, $2, ... refer to capture groups, $<name> for named groups, $& for the whole match, $$ for a literal dollar. Without the g flag only the first match is replaced.

Anything sent to a server?

No. Pattern, flags, test input, and replacement string all run via the browser's RegExp + String APIs. Nothing leaves your device — useful when testing patterns against snippets of customer data, log lines, or PII you don't want to upload to a third-party service.