Regex Tester

Type your pattern in the /pattern/ field and paste your test string in the editor below it. Matches are highlighted in real time as you type. Toggle flags (g, i, m, s, u) using the letter buttons next to the pattern field. The Matches list shows each match value, position, length, and all capture groups.

Regex (regular expressions) is a powerful pattern language for matching text based on characters, classes, quantifiers, and anchors. Glob patterns (used in file systems and shell commands) are simpler, using only * (any characters), ? (one character), and [...] (character sets). A regex like ^src/.*\.tsx$ is the glob equivalent of src/**/*.tsx. Globs cannot express groups, alternation, or lookaheads.

.* is greedy, meaning it matches as many characters as possible. Use .*? for a non-greedy (lazy) match, which stops at the first opportunity. For example, <.*> matches the whole string "<b>text</b>", while <.*?> matches only "<b>".

Without the m flag, ^ matches the very start of the string and $ matches the very end. With the m flag, ^ matches the start of each line and $ matches the end of each line. This is essential when you want to match patterns at line boundaries in multi-line text.

Use (?<name>...) syntax. For example, (?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2}) captures the parts of a date as named groups year, month, and day. This tool shows named group values in the match list alongside numbered groups.

Patterns like (a+)+ on long strings can cause exponential time complexity as the regex engine tries every possible way to match. Avoid nested quantifiers on overlapping character classes. If your test string is large and the page becomes unresponsive, this is the likely cause. This tester has a 10,000-match safety limit to prevent hangs.

Yes. It uses JavaScript's built-in RegExp engine running in your browser. Syntax and behavior may differ from PCRE (PHP, Python), POSIX (grep), or .NET regex. Most common patterns are compatible, but features like variable-length lookbehind assertions (supported in Python but not all JS engines) may behave differently.

Use word boundary anchors: \b before and after the word. For example, \bcat\b matches "cat" in "the cat sat" but not in "caterpillar" or "concatenate". Without the anchors, cat would match the substring in all three. Add the g flag to find all occurrences in a string.

There isn't a technical difference, they describe the same task from two angles. 'Validator' emphasizes checking whether a pattern matches expected input correctly (for example, validating an email format). 'Tester' or 'matcher' emphasizes seeing what a pattern matches against sample text. This tool does both: type a pattern, paste representative input, and confirm it matches (or rejects) what you expect.