Regex Visualizer

A capture group is a part of a regex pattern wrapped in parentheses, like (\d+). It 'captures' the matched text so you can reference it separately from the full match. For example, in (\d{4})-(\d{2}), the first group captures the year and the second captures the month. Capture groups are numbered left to right by their opening parenthesis.

A named capture group uses the syntax (?<name>pattern) to give a group a human-readable name instead of just a number. For example, (?<year>\d{4})-(?<month>\d{2}) lets you access the year and month by name in your code. Named groups make complex regexes much more readable and maintainable.

The common flags are: g (global) — find all matches, not just the first; i (case-insensitive) — match uppercase and lowercase the same; m (multiline) — ^ and $ match start/end of each line; s (dotall) — the dot (.) matches newlines too; u (unicode) — enables full Unicode support including \p{} properties. You can combine flags freely.

The Regex Visualizer focuses on showing you exactly what each match and capture group contains, with color-coded highlighting for multiple matches. The Regex Tester lets you run assertions (expected match / no-match) to build a test suite for your patterns. Use the visualizer to debug and understand a regex, and the tester to validate it against known cases.

Common causes: missing the g flag (only finds first match), greedy vs lazy quantifiers (use +? or *? for lazy), forgetting to escape special characters like . () [] with a backslash, and anchor misuse (^ and $ match line start/end in multiline mode but string start/end otherwise). Try the presets to see working examples, then modify from there.