Regex tester online
Paste a pattern, test it against real text, and see exactly what matches before it reaches production validation.
Turn the tested pattern into a small utility
When a regex becomes part of a validator, parser, or internal helper, DeployPages can host the static tool so the team uses the same tested version.
Deploy a tool siteWhy use an online regex tester?
Regex bugs hide in tiny details: a missing anchor, a greedy quantifier, a flag you forgot, or sample data that looks nothing like production input. A live tester keeps the pattern, flags, matches, and test string visible together so you can fix the actual expression instead of guessing.
Regex cheatsheet
| . | Match any character except a line break |
| \w | Match letters, digits, or underscore |
| \d | Match digits |
| \s | Match whitespace |
| [abc] | Match any listed character |
| [^abc] | Match any character not listed |
| * | Match zero or more times |
| + | Match one or more times |
| ? | Match zero or one time |
| {n} | Match exactly n times |
| {n,} | Match at least n times |
| {n,m} | Match between n and m times |
| ^ | Match the start of a string |
| $ | Match the end of a string |
| \b | Match a word boundary |
| \B | Match a non-word boundary |
| (?=p) | Positive lookahead |
| (?!p) | Negative lookahead |
| g | Global search |
| i | Case-insensitive mode |
| m | Multiline mode |
| s | Dot matches line breaks |
| u | Unicode mode |
Advanced FAQ
What is the difference between greedy and lazy matching?
Greedy matching consumes as much text as possible. Lazy matching adds ? after a quantifier so the engine stops at the earliest valid match.
How should I validate email addresses with regex?
Use regex for a practical first-pass check, but do not treat it as final proof of ownership. A verification flow still matters.
Why does my regex work in one language but fail in another?
Regex engines do not all support the same features. JavaScript, PCRE, Python, Java, and database regex flavors differ on lookbehind, named groups, unicode handling, and escaping rules.
Can a regex create a performance problem?
Yes. Nested quantifiers and ambiguous alternatives can cause excessive backtracking on certain inputs. Test realistic worst-case strings before using a pattern in request validation.