Tester
Build the pattern, apply the right flags, test it against realistic text, and inspect the exact matches and capture groups before you trust it in production code.
Sample patterns
Start with a common regex example if you want to test the matching flow before writing your own pattern from scratch.
Pattern and flags
Enter the regex pattern first, then add only the flags you actually want the JavaScript engine to use.
Add the regex flags you want to use here, like g, i, or m.
/([A-Z])\w+/gTest text
Paste real sample text here so you can see whether the pattern behaves the way you actually need.
Match preview
Review live highlighting to see what the pattern matches, skips, or grabs too aggressively.
Capture groups
Inspect the full match and the captured groups for each result.
Match 1
Full match
Hello
Group 1
H
Match 2
Full match
Regex
Group 1
R
How to Use This Regex Tester
Use the tester as a fast regex workbench: write the pattern, apply the right flags, compare the result against sample text, and inspect the matches before you move the regex into production logic.
Paste or write the pattern
Start with the exact regex you want to test instead of guessing how it behaves in your code editor or terminal.
Turn on the flags you need
Switch flags like global, case-insensitive, multiline, dotAll, or Unicode depending on the kind of matching you expect.
Test against real sample text
Use realistic input so you can see whether the pattern matches what you want, misses data, or grabs too much.
Inspect matches and capture groups
Check the highlighted results and captured groups before you move the pattern into validation, parsing, or replacement logic.
When This Tool Is Most Useful
Regex testing helps most when the pattern looks close to correct, but the match behavior still feels off or too risky to trust without seeing it against real text.
Input validation checks
Test email, username, password, date, and ID patterns before you wire them into forms or API validation.
Log and text extraction
Build patterns for timestamps, IDs, error lines, URLs, and other structured data hiding inside plain text.
Regex debugging under pressure
See when a pattern is too greedy, too narrow, or broken entirely before you waste time chasing the wrong fix.
Capture group verification
Confirm that the groups you plan to use in code actually capture the pieces of text you care about.
How Regex Matching Works
A regular expression is just a pattern. The regex engine reads that pattern and tries to match it against the sample text from left to right based on the rules you wrote.
That means the same pattern can behave very differently depending on anchors, groups, quantifiers, character classes, and flags. A tester is useful because it lets you see those decisions play out immediately instead of guessing from the pattern alone.
What the Main Flags Change
Regex flags are not small details. They often change what gets matched, how many results you see, and whether anchors or dot characters behave the way you expect.
/g
Global matching
Find every match in the sample text instead of stopping after the first one.
/i
Case-insensitive matching
Ignore letter casing when the text can appear in uppercase, lowercase, or mixed form.
/m
Multiline anchors
Make ^ and $ work line by line instead of only at the start and end of the whole string.
/s
DotAll mode
Allow . to match newline characters when the pattern needs to span multiple lines.
Common Regex Pitfalls
Most regex bugs are not syntax bugs. They come from patterns that technically run, but do not match the right text once the input gets messy or the edge cases show up.
A pattern can match too much because a quantifier is greedy when you expected a narrower result.
A validation rule can fail because the right flag was missing, especially g, i, m, or s.
A capture group can look correct at first but still return the wrong substring once real data changes shape.
A regex can work on a toy sample and still break on multiline logs, Unicode text, or edge-case input.
FAQs
What regex engine does this tool use?
It uses the browser’s native JavaScript RegExp engine, so the behavior matches the kind of regex you use in frontend code and many browser-based workflows.Can I test modern JavaScript regex features here?
Yes. This tester is suitable for common JavaScript regex work including flags, capture groups, lookarounds, and other browser-supported pattern features.Does this tool show capture groups?
Yes. It highlights matches and also lists captured groups so you can inspect the exact pieces your pattern returns.Is my test data sent anywhere?
No. Pattern testing happens locally in your browser so the regex and sample text stay on your machine.