Regular Expression (Regex) Tester
Design, evaluate, and test regular expressions in real-time with visual match highlighting, diagnostics, and code generation.
Configure, select, or write regular expressions and set standard modifiers.
Character Classes & Quantifiers
| Char | Definition / Type | Example Matches |
|---|---|---|
^ / $ |
Starts / Ends of line anchor | ^abc$ (exactly "abc") |
. |
Any character except newline | a.c matches "abc", "a1c" |
\d / \w |
Digit [0-9] / Word character [a-zA-Z0-9_] | \d+ matches "42", "99" |
\s |
Whitespace (space, tab, newline) | \s+ matches line breaks/spaces |
+ / * |
1 or more / 0 or more occurrences | a+ matches "a", "aaa" |
? |
Optional element (0 or 1 match) | colou?r matches "color", "colour" |
{n,m} |
Quantifier limits (from n to m times) | \d{2,4} matches "99", "2026" |
Select your active programming language to generate pattern search code using the current configuration.
My Saved Regex Patterns
Access saved regular expressions stored locally in your browser.
Regular Expression (Regex) Tester Guide & FAQs
Understanding Regular Expressions (Regex)
Regular expressions (often shortened to regex) are specialized text patterns used to match character combinations inside string variables. They are standard tools for user-input validation (like emails or telephone numbers), string parsing, and find-and-replace transformations.
A regex pattern is composed of literal characters and metacharacters. Literals match themselves directly, while metacharacters declare special constraints: anchors like ^ (starts of string) and $ (ends of string), character sets like [0-9], word boundaries, and quantifiers specifying repetition limits (e.g. + for 1 or more, ? for optional, or {2,4} for limits).
Modifiers and Compilations
Our configurator tests regex code directly in your browser. By selecting standard modifiers like global g (find all occurrences), case-insensitive i, and multiline m, you can visually trace colorized matching results and ensure your code integrates without compiling errors.
Frequently Asked Questions
What is a regular expression (regex)?
A regular expression is a structured pattern that describes a set of strings. It is widely supported across programming languages and search tools to parse, filter, extract, and replace text occurrences.
What are the common regex flags?
Common flags modify the matching rules: Global g searches for all matches in the text instead of stopping after the first match; Case-insensitive i ignores capitalization; and Multiline m treats start/end anchors relative to each line break.
How do anchors (^ and $) work?
Anchors do not match actual text, but mark position rules: the caret ^ asserts that matches must start at the beginning of a line or string, while the dollar $ asserts they must end at the termination boundary.