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Regex Tester

Regex Tester runs your pattern against any text and highlights every match in place, so you can see exactly what a regular expression captures. It surfaces the match count, each capture group and the index of every hit as you type.

It uses the same regular-expression engine as the browser, so behaviour matches real JavaScript. Everything runs locally — your patterns and test data never leave the page.

3
Matches
0
Capture groups
g
Active flags

Highlighted matches

Contact us at hello@example.com or support@multitool.dev.
Invalid: foo@bar and plain text without an address.
Another one: admin@site.io works too.

Match list

hello@example.comindex 14
support@multitool.devindex 35
admin@site.ioindex 123

Tip: matches are always collected globally so every occurrence is highlighted. Toggle the g flag to see it reflected in the pattern label above.

How to use Regex Tester

  1. 1

    Enter your pattern

    Type a regular expression in the pattern box. You don't need the surrounding slashes — just the expression itself.

  2. 2

    Choose flags

    Toggle the g, i, m, s, u and y flags. Matches are always collected globally for highlighting, and the active flags appear next to your pattern.

  3. 3

    Read the results

    Paste your test string to see matches highlighted, the total match count, and a breakdown of each capture group with its index.

What is a regular expression?

A regular expression — or regex — is a compact pattern language for describing text. Instead of searching for a fixed word, you describe a shape: "a digit followed by two letters", "anything between quotes", or "a valid email address". Engines then scan your text and return every span that fits the shape.

Regular expressions power find-and-replace in editors, input validation in forms, log parsing, and search across millions of files. Because the syntax is dense, a tester that shows matches and groups in real time is the fastest way to get a pattern right without trial-and-error in code.

Understanding flags and capture groups

Flags change how a pattern is applied. The global flag (g) finds every match rather than stopping at the first; ignore-case (i) makes letters case-insensitive; multiline (m) lets ^ and $ match the start and end of each line; dotall (s) lets the dot match newlines; unicode (u) enables full Unicode handling; and sticky (y) anchors each match to the position where the last one ended.

Capture groups — the parts of your pattern wrapped in parentheses — pull out sub-sections of each match. This tester lists every group by number ($1, $2, …) and shows named groups too, so you can confirm a pattern extracts exactly the fields you expect before wiring it into code.

Frequently asked questions

Which regex syntax does this use?
It uses the JavaScript (ECMAScript) regular-expression engine built into your browser, so any pattern that works here works the same way in JavaScript and TypeScript.
Why are matches highlighted even without the global flag?
To highlight every occurrence, the tester always iterates globally internally. The flags you toggle are still shown beside the pattern so you can copy the exact expression you intend to use.
Does it support capture groups?
Yes. Each match lists its numbered capture groups and any named groups, along with the match's index in the test string.
Is my data sent anywhere?
No. Matching runs entirely in your browser; your pattern and test text never leave the page.

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