Regex Tester

What are Regular Expressions?

Regular expressions (regex) are patterns used to match character combinations in strings. They provide a powerful and flexible way to search, validate, extract, and manipulate text. While the syntax can look intimidating at first, mastering even basic patterns will dramatically improve your text processing capabilities.

Common Regex Patterns

• \d — Matches any digit (0-9). Use \d{3} to match exactly three digits.
• \w — Matches any word character (letters, digits, and underscore). Use \w+ to match a complete word.
• \s — Matches any whitespace character (spaces, tabs, newlines).
• . — Matches any single character except newline. Use .* to match anything (greedy) or .*? for lazy matching.
• ^ and $ — Anchor to the start and end of a line respectively. ^Hello matches lines starting with Hello.
• [abc] — Character class matching any one of the listed characters. [a-z] matches any lowercase letter.
• (pattern) — Capturing group that extracts the matched text for later use. (?:pattern) is a non-capturing group.

Regex Testing Tips

• Start with simple patterns and build up gradually. Test each component separately before combining them.
• Use the gi flags for global matching (find all matches, not just the first) and case-insensitive matching.
• Be careful with greedy quantifiers (*, +) — they match as much as possible. Add ? after them for lazy matching.
• Test edge cases including empty strings, very long inputs, and strings with special characters.
• Use online regex references and cheat sheets until patterns become familiar.