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Regex Tester

Test and debug regular expressions in real-time. See match highlighting, capture groups, and replacement previews — all running instantly in your browser.

//gi
2 matches

Match preview:

Contact us at hello@utulio.com or support@example.org

Matches (2)
  • hello@utulio.comat index 14groups: helloutulio.com
  • support@example.orgat index 34groups: supportexample.org

Getting Started with Regular Expressions

Regular expressions are one of the most powerful tools in a developer's toolkit. Whether you're validating form inputs, parsing log files, transforming text, or extracting data, regex provides a concise and universal solution.

Start with simple patterns and build complexity. A pattern like \d+ matches one or more digits. Add grouping: (\d3)-(\d4) matches a phone number and captures the two parts separately. Use flags like i for case-insensitive matching and g to find all occurrences.

This tester uses the standard JavaScript RegExp engine, so patterns work exactly as they would in Node.js, browser JavaScript, and most modern programming environments.

Regex Tester FAQs

What is a regular expression?
A regular expression (regex) is a sequence of characters that defines a search pattern. Regex can match specific text, validate formats (email, phone, URL), extract data, and perform find-and-replace operations. They are supported in virtually every programming language.
What do the regex flags mean?
The most common flags are: g (global — find all matches, not just the first), i (case insensitive), m (multiline — ^ and $ match line boundaries instead of string start/end), and s (dotall — makes . match newline characters too). You can combine multiple flags.
What's the difference between * and +?
* means "zero or more" repetitions. It matches even if the pattern appears zero times. + means "one or more" repetitions — it requires at least one match. For example, \d* matches an empty string, while \d+ requires at least one digit.
How do capture groups work?
Parentheses () create capture groups that extract specific parts of a match. For example, the pattern (\w+)@(\w+\.\w+) applied to "hello@example.com" captures "hello" as group 1 and "example.com" as group 2. You can reference captured groups in replacement strings with $1, $2, etc.
Is my data sent anywhere?
No. This regex tester runs entirely in your browser using the native JavaScript RegExp engine. Your patterns and test strings are never transmitted to any server. This makes it safe to test sensitive data patterns.
Why does my regex match nothing?
Common reasons: (1) the pattern is case-sensitive and your text has different casing — try the i flag, (2) special characters like . * + ? need escaping with \ if meant literally, (3) you're missing the g flag so only the first match is found, (4) anchors (^ $) are restricting the match too tightly.

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