Programming interactive tool

Regular Expressions Interactive Demo

Test regex patterns, inspect capture groups, preview replacements, and learn common text-processing patterns in one browser-first teaching tool.

Local browser processingCapture groupsReplacement preview

Current run

Ready

Matches

Flags

The regex runs inside a browser worker and stops slow patterns to protect the page.

Try it yourself

Pattern, flags, and input text

Regex pattern

//gi

Test text507 / 20,000 characters

Examples

Load a teaching pattern

Safety note

Regex can be computationally expensive. This tool limits pattern length, text size, and execution time. It is built for learning, teaching, and safe text examples.

Live results

Highlighted matches

Regular expressions are powerful tools for text processing.

CONTACT INFO:
- Emails: john.doe@example.com, support@company.co.uk, test_user-123@sub.domain.org
- Phone: (555) 123-4567, 555.123.4567, 5551234567, +1-555-123-4567

WEB AND TECH:
- URLs: https://www.example.com, http://subdomain.site.com/path?query=value
- IP addresses: 192.168.1.1, 10.0.0.255, 255.255.255.0

DATES AND CODE:
- Dates: 01/15/2023, 2023-05-18, 15-Jan-2023
function hello() { return "Hello, world!"; }
print(f"The answer is {42}")

Capture groups

Match table

Matches and capture groups will appear here after the pattern matches the text.

Replace mode

Preview replacement

Replacement text

Replacement preview appears here.

How to teach it

Regex learning path

1. Start with literal text, then introduce character classes like \d and \w.
2. Add quantifiers such as +, *, and {n,m}.
3. Use capture groups to extract meaningful parts, such as date components or usernames.
4. Show flags one at a time so students see how matching behavior changes.

Reference

Common regex tokens

Token	Meaning	Example
.	Any character except newline, unless DotAll is enabled.	a.c matches abc
^	Start of string, or start of line with multiline mode.	^Error
$	End of string, or end of line with multiline mode.	done$
\d	Any digit from 0 to 9.	\d{4}
\w	Word character: letter, digit, or underscore.	\w+
\s	Whitespace such as spaces, tabs, and line breaks.	\s+
[abc]	One character from a set.	[aeiou]
[^abc]	One character not in a set.	[^0-9]
*	Zero or more repetitions.	go*gle
+	One or more repetitions.	\d+
?	Zero or one repetition, or lazy mode after another quantifier.	colou?r
{n,m}	Between n and m repetitions.	\d{2,4}
(...)	Capture a group for reuse or inspection.	(cat\|dog)
(?<name>...)	Named capture group.	(?<year>\d{4})
\|	Either the left or right alternative.	jpg\|png