Regex Tester & Builder

Type your pattern into the field at the top, toggle any flags (g, i, m, s…), and paste your text into the test area. Matches highlight live as you type — there is no run button. Each match, its position and capture groups appear in the Matches tab instantly.

The tester is fully reactive: it re-evaluates your pattern against the test string on every keystroke and highlights matches in real time. That makes debugging far faster than a submit-and-wait flow.

It runs the native JavaScript (ECMAScript) regex engine in your browser, so behaviour matches Node.js and every modern browser exactly. The Code tab then translates your pattern into Python, PHP, Java, C#, Go, Ruby, Rust, Perl and grep syntax.

g = global (all matches), i = case-insensitive, m = multiline (^ and $ per line), s = dotall (. matches newlines), u = unicode, y = sticky, d = match indices. Hover each flag button for a tooltip.

Wrap part of a pattern in ( ) to capture it; each match lists its groups as $1, $2… Use (?<name>…) for named groups, which appear as «name». In the Replace tab you can reference them with $1 or $<name>.

Yes — open the Replace tab and enter a replacement string. It supports $1, $<name>, $& (whole match) and more, and shows the substituted result live with a count of replacements.

No. All matching, replacing and code generation happen entirely in your browser. Nothing you type is uploaded, so it is safe for sensitive text.

Some patterns (e.g. nested quantifiers like (a+)+) can take exponential time on certain inputs, freezing the engine. The tester caps iterations to stay responsive — if a pattern feels slow, simplify nested quantifiers or make them possessive/atomic in engines that support it.

A practical pattern is [a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,} — one or more name characters, an @, a domain, a dot and a 2+ letter TLD. Load it from the Library tab and tweak it live. For strict RFC validation, prefer a dedicated validator.

Use \d+ with the global flag to grab every run of digits, or -?\d+(?:\.\d+)? to also catch negatives and decimals. Paste your text and the Matches tab lists every number it finds.

Yes — it gives you the essentials (live highlighting, capture groups, replace, a plain-English explainer, code export and a pattern library) with no sign-up, no ads and everything running locally in your browser. It uses the JavaScript engine, so it is ideal for JS/TypeScript/Node work and for learning regex.

Enable the m (multiline) flag so ^ and $ match the start and end of each line, and the s (dotall) flag so . also matches newline characters. Toggle both with the flag buttons above the test area.

Almost always flags or flavour. Make sure you set the same flags (g, i, m, s) in your code, and remember engines differ: this tester uses JavaScript/ECMAScript, while Python (re), PCRE/PHP, and Go/Rust (RE2, no lookbehind/backreferences) vary. The Code tab generates flag-correct snippets for each language.

Wrap the parts you want in parentheses ( ). Each match then lists its groups as $1, $2…; use (?<name>…) for named groups shown as «name». In code, read them from the match array (JS), .group(n) (Python) or matcher.group(n) (Java).

Greedy quantifiers (*, +, {n,}) match as much as possible; adding ? makes them lazy (*?, +?) so they match as little as possible. For example, on <a><b> the pattern <.+> is greedy and matches the whole string, while <.+?> matches just <a>.

The Reference tab is a built-in cheat sheet covering anchors, character classes, quantifiers, groups and lookarounds, and the Library tab has ready-made patterns (email, URL, IP, date, password and more) you can load and tweak live.