Regex Tester Online — Test Regular Expressions Instantly

Q: What is a regular expression (regex)?

A regular expression (regex) is a sequence of characters that defines a search pattern. It is used to find, match, or replace text in strings. Regex is supported in nearly every programming language and many text editors.

Q: How do I test a regular expression?

Enter your pattern in the pattern field and your test string in the text area below. The tool will automatically highlight all matches and show a list of matches with their positions and captured groups.

Q: What regex flags should I use?

The most common flags are: g (global) to find all matches, i (case insensitive) to ignore case, m (multiline) to make ^ and $ match line boundaries, and s (dotAll) to make . match newlines.

Q: How do I make a case insensitive regex?

Add the i flag to your regex. For example, the pattern /hello/i will match 'hello', 'Hello', 'HELLO', and any other combination of upper and lowercase letters.

/ /

Type a pattern above, then paste test text here

How to Use the Regex Tester

Enter your pattern — type your regular expression between the / slashes
Set flags — adjust the flags after the closing slash (default: g for global match)
Paste test text — type or paste the string you want to test in the editor below
See instant results — matches highlight in the preview; each match is listed with its index, length, and captured groups
Replace mode — click Replace to test substitution patterns using back-references like $1, $2

Regex Flags Reference

Flag	Name	Description	Example
g	Global	Find all matches instead of stopping at the first	`/cat/g` matches every "cat"
i	Case insensitive	Match regardless of upper or lower case	`/hello/i` matches "Hello", "HELLO"
m	Multiline	Makes `^` and `$` match start/end of each line	`/^\d+/m` matches digits at line starts
s	DotAll	Makes `.` match newline characters too	`/a.b/s` matches "a\nb"
u	Unicode	Enables full Unicode matching	`/\u{1F600}/u` matches emoji
y	Sticky	Matches only at the current `lastIndex` position	Used for sequential parsing

Common Regex Patterns

Click Use to load any pattern directly into the tester:

Name	Pattern	Flags

Frequently Asked Questions

What is a regular expression (regex)?

A regular expression is a sequence of characters that defines a search pattern. It is used to find, match, validate, or replace text. Regex is supported in virtually every programming language and text editor, making it one of the most versatile text tools available.

How do I test a regular expression?

Enter your pattern in the field above and paste your test string in the editor. Results update automatically as you type — matches are highlighted in the preview and listed below with their character position, length, and any captured groups.

What regex flags should I use?

The most commonly used flags are g (global — find all matches), i (case insensitive), m (multiline — ^ and $ match line boundaries), and s (dotAll — dot also matches newlines). Combine freely, e.g. gi for global case-insensitive matching.

How do I make a case insensitive regex?

Add the i flag. With pattern hello and flags gi, the tester will match "hello", "Hello", "HELLO", and every other capitalization variant.

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