Regex Tester

Test regular expressions with live matches, capture groups, and replacements. Run locally or via Django API.

Use Django API

Regular Expression (without slashes)

Flags: g i m s u y

Presets:

Replacement (optional)

Supported: $& entire match, $1…$99 capture groups, $$ literal dollar.

Test String

Tip: Ctrl/Cmd+Enter runs the test.

Matches & Replace Preview

Idle

Highlighted input

Replacement output

Capture Groups

#	Match	Index	Groups

Regular Expressions — A Practical Guide

Regular expressions (regex) describe text patterns for validation, extraction, and search/replace. Use anchors for validation, and test on realistic samples.

Common tokens

. any char (add s for dotall)
\\d \\w \\s digits/word/space
^ $ line anchors (m flag)
(...) capture, (?:...) non‑capture
[abc] class, [^abc] negated

Useful patterns

Email: ^[\\w.%+-]+@[\\w.-]+\\.[A-Za-z]{2,}$
URL: https?:\\/\\/[\\w.-]+(?:\\/[\\w./%#?=&-]*)?
IPv4: \\b\\d{1,3}(?:\\.\\d{1,3}){3}\\b

Pitfalls & tips

Watch for catastrophic backtracking; simplify where possible.
Use u for Unicode and s for multiline dot.
Benchmark on long inputs; the API enforces timeouts for safety.

Replacement Cheatsheet

$& = full match
$1 … $99 = capture groups
$$ = literal “$”

Example

Pattern:  (\\d{4})-(\\d{2})-(\\d{2})
Replace:  $3/$2/$1
Input:    2025-08-19 → Output: 19/08/2025