How to use the Regex Tester
- Type a pattern and flags.
- Paste test text.
- Review highlights and groups.
How it works
Flags: g global, i ignore case, m multiline, s dotAll, u unicode, y sticky, d indices. Parentheses create capture groups; \b marks word boundaries; \d matches digits.
Worked example
The default email pattern finds hello@billgen.com and support@example.org in the sample text.
Good to know
Syntax errors are shown immediately.
Matches are capped at 1,000 to keep the page responsive.
Regex flavors differ between languages; this tests JavaScript only.
Frequently asked questions
It finds all matches instead of stopping after the first.
Mostly similar but not identical; lookbehind and named groups differ.
Nested quantifiers can cause catastrophic backtracking.
BillGen provides general-purpose tools; verify important outputs before relying on them.