Regex Tester
Test and debug regular expressions against sample text with live match highlighting.
Knowledge Base & Educational Companion: Understanding regular expressions
A regular expression (regex) is a pattern that describes a set of strings. Regex powers search, validation and text extraction across almost every programming language.
1. Patterns and metacharacters
Characters like '.', '*', '+' and '\d' match categories of text rather than literal characters, letting one short pattern match many possible strings.
2. Flags change behaviour
Flags like 'g' (global), 'i' (case-insensitive) and 'm' (multiline) modify how the engine searches, turning a single-match test into a full sweep of the input.
3. Capture groups
Parentheses create capture groups that extract parts of a match — the backbone of parsing dates, URLs and structured text out of raw strings.
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