Regex Tester & Explainer

How To Use

1. Enter a regular expression in the Pattern field, for example \d{4}-\d{2}-\d{2}.
2. Tick the flags you need: g for all matches, i to ignore case, m for multiline anchors, and s so . matches newlines too.
3. Paste your Test text into the textarea.
4. Click Test to see the match count, highlighted matches, and the capture groups for each match.
5. Pick an example from Load a demo and click Load demo to try a battle-tested pattern instantly — email, URL, IPv4, hex color, UUID, dates, times, HTML tags, repeated words, and more.
6. Use Get code to turn your pattern into a ready-to-paste snippet for JavaScript, Python, Java, or C#: it includes a one-line yes/no Is match check, a whole-text Fully matches validation, an iteration over every match with its capture groups — and, when you filled the replace field, the replace call with the right syntax per language.
7. Click Explain for a plain-language breakdown of every piece of your pattern.
8. Click Copy matches to put a plain-text summary on your clipboard.

Usage Example

Say your pattern is (\d{2})/(\d{2})/(\d{4}) and your test text is:

Orders ship on 14/03/2026 and 02/09/2026.

Clicking Test reports 2 matches. Both dates are highlighted, and the capture groups for the first match are group 0: 14/03/2026, group 1: 14, group 2: 03, and group 3: 2026 — the day, month, and year you wrapped in parentheses. Then click Explain and every token is decoded: two digits, a slash, two digits, a slash, and four digits.

Frequently Asked Questions

What is a regular expression (regex)?

A regular expression is a compact pattern language used to describe and match text. Instead of searching for one fixed string, you describe a shape: for example \d{4} means "exactly four digits" and [a-z]+ means "one or more lowercase letters". Regex powers validation, searching, and text extraction in almost every programming language, and this tester lets you experiment with them instantly.

Does the Explainer understand every regex syntax?

No. The Explainer covers a deliberately bounded subset: literal characters, the dot, the shorthand classes \d \w \s \b (and their uppercase negations), character classes such as [abc] and [^…], capturing and non-capturing groups, the quantifiers + * ? {n} {n,} {n,m}, the anchors ^ $, and the alternation |. More advanced constructs — lookahead, lookbehind, named groups, and Unicode properties — are marked [not explained] in the output so you always know exactly what was decoded and what wasn't. The tester itself still matches them correctly; only the textual explanation is limited.

Which flags are supported?

The tool exposes the four most useful JavaScript regex flags: g (global — find every match instead of stopping at one), i (case-insensitive matching), m (multiline, so ^ and $ match line starts and ends), and s (dotall, letting the dot match newline characters).

Why is there no network involved?

Matching and explanation happen entirely in your browser with native JavaScript — nothing is sent to a server and nothing is uploaded anywhere. That makes the tool fast, private, and safe to use with sensitive or proprietary text that you would never want leaving your machine.

What does the g flag do?

Without g, many engines stop after the first match. With g (global), the tester scans the whole subject and counts every non-overlapping match, then highlights all of them. For counting and highlighting every occurrence, you will normally want g enabled.

How do I read the capture groups?

Parentheses in a pattern create capture groups. In the output, group 0 is always the entire match, and group 1, group 2, and so on are each parenthesized part in order. For example in (\d{2})-(\d{2}) against 12-34, group 1 is 12 and group 2 is 34. A group that did not participate in a match is shown as (no match).

Can I use my regex in JavaScript, Python, Java, or C#?

Yes — the <strong>Get code</strong> panel generates a ready-to-paste snippet for JavaScript, Python, Java, and C#. Each snippet includes a one-line yes/no check for "does this appear anywhere" (regex.test in JavaScript, pattern.search in Python, matcher.find in Java, Regex.IsMatch in C#) plus a full-text validation check for "does the ENTIRE text match" (anchored ^…$ in JavaScript and C#, pattern.fullmatch in Python, matcher.matches in Java), then iterates every match with its capture groups, and includes a replace call when you have filled the replace field. The generator handles the cross-language differences for you: flags become the right per-language form (re.IGNORECASE in Python, Pattern.CASE_INSENSITIVE in Java, RegexOptions.IgnoreCase in C#), the pattern is escaped per language (raw strings in Python, doubled backslashes in Java strings, verbatim strings in C#), and replacement tokens are translated where they differ ($1 becomes \g&lt;1&gt; in Python). The snippet is a correct string embedding — dialect support for exotic constructs is still up to your language version.

What demos are included?

The demo picker ships with ten battle-tested patterns: ISO dates, email addresses, URLs, IPv4 addresses, hex colors, UUIDs, 24-hour times, HTML tags, repeated words (showing a backreference), and numbers with thousand separators. Loading a demo fills the pattern, flags, and test text — and, where it makes sense, a replacement — so you can see a complete working example in one click, then edit it into your own.