Regular Expression Builder
Construct, test, and debug regex patterns. Includes a comprehensive library of patterns for validation, extraction, and data processing.
About
Regular expressions provide a powerful method for pattern matching within strings. Developers frequently use them for form validation or log file parsing and data extraction tasks. The syntax is notoriously dense. A single missing character often breaks the entire logic. Debugging raw patterns without a visual aid consumes valuable development time. This tool provides a structured environment to build and test patterns against real data samples.
Understanding the distinction between greedy and lazy quantifiers prevents performance issues. Catastrophic backtracking remains a risk in poorly constructed expressions. This builder allows users to verify matches safely before deploying code to production environments. It supports standard JavaScript syntax which aligns closely with PCRE standards used in PHP and Python.
Formulas
Regular expressions formally describe a set of strings known as a Regular Language. The operations follow specific algebraic rules within set theory.
Union (Alternation):
Concatenation:
Reference Data
| Token | Description | Example Match |
|---|---|---|
| . | Any Single Character (except newline) | a, 1, % |
| \d | Digit (0-9) | 5, 9 |
| \w | Word Character (a-z, A-Z, 0-9, _) | A, b, _ |
| \s | Whitespace (space, tab, newline) | (space) |
| ^ | Start of String Anchor | Beginning only |
| $ | End of String Anchor | End only |
| [abc] | Character Set (Any of a, b, or c) | a or b |
| [^abc] | Negated Set (Anything except a, b, c) | d, 1 |
| * | Zero or more times | aa, (empty) |
| + | One or more times | aa |
| ? | Zero or one time (Optional) | a, (empty) |
| {n,m} | Range Quantifier (n to m times) | aaaa |
| (...) | Capturing Group | Stores match |
| (?:...) | Non-capturing Group | Groups logic only |
| x|y | Alternation (OR) | x or y |