About Regex Cheatsheet

Searchable reference of regex syntax with live examples. Part of the DevTools Surf developer suite. Browse more tools in the Text / String collection.

Use Cases

• Looking up lookahead syntax while writing validation patterns
• Referencing character class shortcuts during log file parsing
• Teaching regex concepts to teammates with live examples
• Quickly finding the correct flag for case-insensitive matching

Tips

• Use the search bar to find specific patterns like lookaheads
• Click any example to see it highlighted in the live preview
• Bookmark this page as a quick regex reference while coding

Fun Facts

• Regular expressions were formalized by mathematician Stephen Cole Kleene in 1951 as part of his work on formal language theory.
• Ken Thompson implemented regex in the QED text editor in 1968, which later influenced grep — whose name stands for 'globally search for a regular expression and print.'
• Perl's regex engine, introduced in 1987, became so influential that most modern regex flavors are described as 'Perl-compatible' (PCRE).

FAQ

Which regex flavor does this cover?

PCRE/JavaScript/Python compatibility — the common subset that works in 90% of languages. Engine-specific features (Perl's lookbehind variants, .NET balancing groups) are noted separately.

Does it include named groups?

Yes — `(?<name>pattern)` with the syntax variations across languages (JS uses `(?<name>`, Python uses `(?P<name>`). Copy the right one for your context.

What about character classes?

Full coverage: `\w`, `\d`, `\s`, `\b`, POSIX classes `[[:alpha:]]`, and Unicode property escapes `\p{L}`.

Is there a performance guide?

Yes — notes on catastrophic backtracking patterns (nested quantifiers, overlapping alternations) and how to rewrite them. Essential for regex that processes user input.