1. Enter a pattern
Type a regular expression without the surrounding slash characters. For example, use \bword\b instead of /\bword\b/g.
Free regex tester · developer tool · browser-based
Regex Tester Online
Test JavaScript regular expressions against sample text, inspect match counts and capture groups, try common flags, and catch invalid pattern errors before using a regex in code.
Regex pattern and test text
Enter a JavaScript regex pattern without wrapping slashes, choose flags, and add sample text.
This tester uses your browser's JavaScript RegExp behavior. Other regex engines such as PCRE, Python, Java, and .NET may differ.
Match results
Review matches, index positions, capture groups, and pattern errors.
Ready. Enter a regex pattern and sample text to test matches.
0Matches
gFlags
0Groups
ReadyPattern status
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How to use the Regex Tester
Use the tester as a lightweight browser-based JavaScript RegExp sandbox before copying a pattern into code.
2. Choose flags and text
Select flags such as global, case-insensitive, multiline, dotAll, or unicode, then paste realistic sample text.
3. Review matches
Check the match count, positions, capture groups, and invalid-pattern messages before using the regex elsewhere.
Practical regex testing use cases
Regex testing is most useful when you check a pattern against messy, realistic examples rather than one perfect string.
Validate simple patterns
Try email-like, URL-like, ID-like, or label patterns before adding them to scripts, forms, or cleanup workflows.
Debug extraction behavior
Inspect which text is matched, where each match starts, and whether capture groups return the values you expect.
Compare flag behavior
Test how global, case-insensitive, multiline, dotAll, and unicode flags change JavaScript RegExp matching.
Regex behavior and safety notes
This tool uses browser JavaScript RegExp behavior. Do not assume every programming language or regex engine will match exactly the same way.
Engine differences matter
PCRE, Python, Java, .NET, and browser JavaScript regex engines can differ in supported syntax and edge-case behavior.
Avoid heavy patterns
Very large input and poorly designed patterns can be slow. Test with realistic examples and simplify risky expressions.
Use parsers when needed
Regex is good for targeted matching, but complex nested HTML, JSON, or programming languages usually need parsers.
Regex Tester FAQ
What regex engine does this tester use?
It uses the browser JavaScript RegExp engine. Other engines such as PCRE, Python, Java, and .NET may support different syntax or edge-case behavior.
Can this tester show capture groups?
Yes. When a match includes capture groups, the results show numbered groups under the matching line.
What happens if my pattern is invalid?
The tool shows a readable invalid-pattern message and clears the error after you fix the pattern.
Can I use regex to parse HTML or JSON?
Regex can be useful for small targeted matches, but complex nested HTML or JSON should be handled with a parser or a dedicated formatter.