Online Regex Tester & Debugger

A Regular Expression (often shortened to "regex" or "regexp") is a sequence of characters that specifies a search pattern. Instead of searching for a literal string, you can define a pattern to find and manipulate text in incredibly powerful ways. While the syntax can look intimidating at first, understanding the core concepts of regex will make you a more efficient and effective developer.

Our Online Regex Tester is the perfect sandbox for learning, building, and debugging your patterns. Because it runs entirely in your browser, your test data remains completely private. You get instant feedback as you type, with matches highlighted directly in your test string and a detailed breakdown of all captured groups.

1. Character Classes & Sets

These allow you to match one character from a specific set.

• [abc]: Matches either 'a', 'b', or 'c'.
• [a-z]: Matches any lowercase letter.
• \\d: A shorthand that matches any digit (0-9).
• \\w: Matches any "word" character (letters, numbers, and underscore).
• . (Dot): A wildcard that matches any single character except a newline.

2. Quantifiers

Quantifiers specify how many times the preceding character or group should appear.

• +: One or more times.
• *: Zero or more times.
• ?: Zero or one time (makes it optional).
• {n}: Exactly 'n' times. e.g., \\d{4} matches four digits.
• {n,m}: Between 'n' and 'm' times.

3. Anchors

Anchors match a position, not a character.

• ^: Matches the beginning of the string.
• $: Matches the end of the string.
• \\b: Matches a word boundary (the edge between a word and a space or punctuation).

4. Grouping & Capturing

Parentheses () create a capturing group. This lets you extract a specific part of the match or apply a quantifier to a whole group of characters. For example, in (\\d4)-\\d2, the (\\d4) captures the year. Our tool shows these captured groups in the "Matches" section.