1. Regular expression
Enter your regular expression and select the flags you want to use.
\d+ rather than /\d+/g.
2. Test text
Enter the text you want to search. Matching sections will be highlighted below.
3. Match highlighting
Matched portions of your test text are highlighted.
4. Match details and capture groups
Inspect each match, its position in the text, and the values captured by your groups.
| # | Match | Start | End | Capture groups |
|---|---|---|---|---|
| Run a test to display match details. | ||||
5. Test replacement
Test how your regex behaves when replacing matching text. JavaScript replacement syntax is supported.
$& inserts the entire match.
$1 inserts the first capture group.
$$ inserts a literal dollar sign.
Common regex examples
Select a pattern to load it into the tester.
Regular expression quick reference
| Expression | Meaning | Example |
|---|---|---|
. |
Any character except line terminators, unless using the s flag. | a.c |
\d |
A digit from 0 to 9. | \d+ |
\w |
A word character: letters, digits and underscore. | \w+ |
\s |
Whitespace characters. | \s+ |
^ |
Beginning of input or line with m flag. | ^Hello |
$ |
End of input or line with m flag. | end$ |
* |
Zero or more repetitions. | ab* |
+ |
One or more repetitions. | \d+ |
? |
Zero or one repetition. | colou?r |
{n,m} |
Between n and m repetitions. | \d{2,4} |
[abc] |
Any one character from the set. | [aeiou] |
[^abc] |
Any character not in the set. | [^0-9] |
(abc) |
Capturing group. | (\d{4}) |
(?:abc) |
Non-capturing group. | (?:https?) |
| |
Alternation (OR). | cat|dog |
\b |
Word boundary. | \bcat\b |
(?=...) |
Positive lookahead. | \d(?=px) |
(?!...) |
Negative lookahead. | \d(?!px) |
JavaScript regex flags explained
g - Global
Find all matches instead of stopping after the first match.
i - Ignore case
Match uppercase and lowercase letters without distinguishing between them.
m - Multiline
Make the beginning and end anchors work at individual line boundaries.
s - DotAll
Allow the dot character to match line terminators as well.
u - Unicode
Enable Unicode-aware regular expression processing.
y - Sticky
Require each match to start at the current regular expression position.
d - Match indices
Expose start and end indices for the complete match and its capture groups.
Frequently Asked Questions
What is a regular expression?
A regular expression, often called regex or regexp, is a pattern used to search, match, validate or manipulate text. It is commonly used in programming, data processing, form validation and text analysis.
How do I test a regular expression?
Enter a regex pattern, select the desired flags, and paste your test text into the text field. The tester highlights matches and displays their positions and capture groups.
What are capture groups?
Capture groups are sections of a regular expression enclosed
in parentheses. They allow you to extract specific parts of a match.
For example, (\d{4})-(\d{2})-(\d{2}) captures the
year, month and day separately.
What is the difference between global and non-global matching?
A global expression using the g flag finds multiple
matches. Without the global flag, the tester returns only the first
match.
Does this tester use JavaScript regex syntax?
Yes. It uses the regular expression engine built into JavaScript. Some syntax supported by other regex engines, such as certain PCRE-specific features, may not work here.
Can I use this tool to validate email addresses?
You can test basic email-like patterns, but email validation is more complicated than a single regular expression. For important applications, combine reasonable client-side checks with server-side validation and email confirmation.
Is my test text uploaded?
No. This tool performs regex matching directly in your browser. The entered pattern and test text are not sent to the LifeAfterFlex server.
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