Regex Tester
Test and debug regular expressions instantly in your browser. See live match highlighting, capture groups, replacements, and match details.
How to Use the Regex Tester
- Enter your regular expression pattern in the pattern input field between the `/` delimiters
- Toggle the regex flags you need — `g` for global matching is enabled by default
- Type or paste your test string in the test string area
- All matches are highlighted instantly in the preview panel below the test string
- The Match Results panel shows every match with its position and capture group values
- Switch to Replace Mode to test your replacement string with `$1`, `$2`, and `$&` references
Understanding Regex Flags
Finds all matches rather than stopping after the first match.
Matches regardless of whether characters correspond to upper or lowercase.
Changes ^ and $ to match the start and end of any line.
Makes the . character match newline characters as well.
Treats the pattern as a sequence of Unicode code points.
Generates array indices for substring matches.
Capture Groups Explained
Regular capture groups `()` capture the matched text and make it available as `$1`, `$2` etc. in replacements and as numbered groups in match results.
Advanced: Non-capturing groups `(?:)` group without capturing. Named groups `(?<name>)` let you reference matches by name. All group types are shown in the match results panel.
Common Use Cases for Regex
Trust and Privacy Notice
All regex processing happens entirely in your browser using JavaScript's native RegExp engine. No patterns or test strings are ever sent to any server. Your sensitive data remains completely private.
Frequently Asked Questions
What is a regular expression?
A regular expression (regex) is a sequence of characters that defines a search pattern. It is used to find, match, extract, validate, and replace text in strings. Regular expressions are supported in virtually every programming language and are essential for text processing tasks.
How do I test a regex pattern online?
Enter your regex pattern in the pattern field, choose your flags, and type or paste your test string. All matches are highlighted instantly in the preview panel and listed with full details including position and capture groups.
What are regex capture groups?
Capture groups are portions of a regex pattern enclosed in parentheses (). They capture and return the matched portion of each group separately. For example the pattern (\w+)@(\w+) on test@example captures group 1 as test and group 2 as example. Named groups use the syntax (?<name>pattern).
What does the global flag g do in regex?
The global flag g makes the regex find all matches in the string instead of stopping after the first match. Without the g flag only the first match is returned. Most practical use cases require the g flag to be enabled.
How do I use regex for text replacement?
Switch to Replace Mode using the tab above the test string. Enter your replacement string in the replacement field. Use $1 $2 for capture groups, $& for the full match, $` for the text before the match, and $' for the text after. The replacement result updates instantly.
What regex flavor does this tester use?
This tester uses JavaScript's native RegExp engine, which follows the ECMAScript regex specification. It supports all standard regex features including lookaheads, lookbehinds, named capture groups, and Unicode mode. Patterns tested here will work directly in JavaScript and TypeScript code.
Can I share my regex pattern with someone?
Yes. Click the Share button to generate a URL that encodes your current pattern, flags, and test string. Anyone with the link can open the tool with your exact regex pre-loaded.
Is this regex tester free?
Yes, completely free with no account or signup required. All regex processing happens entirely in your browser using JavaScript's native RegExp engine. No data is ever sent to any server.
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