Regex Tester & Visualizer

Practical guide

Using the Regex Tester

Test patterns, flags, and capture groups.

Pattern: \b[A-Z][a-z]+\b
Text: Ada met Grace

Matches: Ada, Grace

Patterns use JavaScript RegExp syntax, which differs from some other regex engines.
This tool tests matches; it does not prove a pattern is safe from catastrophic backtracking.

SEO & developer education

A fast browser-based regex validator for debugging expression logic, flags, and captured groups in real time.

The tester compiles the user pattern in the browser using JavaScript's native RegExp engine for fast visual feedback.

Flag toggles change matching behavior instantly, helping developers compare g, i, m, and s semantics without a manual script.

Each match includes the exact text plus capture group values so debugging complex patterns is faster and clearer.

The pattern suggestions speed up common validation tasks like email extraction, URL discovery, and date matching.

Test a patternJavaScript

const pattern = /[A-Z][a-z]+/g;
const text = "Alpha Beta gamma";
console.log([...text.matchAll(pattern)].map((m) => m[0]));

Pattern extraction in PythonPython

import re

text = "Alpha Beta gamma"
for match in re.finditer(r"[A-Z][a-z]+", text):
    print(match.group(0))

Use shell grep for quick validationcURL

echo "Alpha Beta gamma" | grep -Eo '[A-Z][a-z]+'

Remember that the g flag changes matching behavior by iterating across all matches instead of returning just the first one.
If a pattern unexpectedly fails, consider whether a character class or escaping issue is preventing the match.
Use the s flag when you want . to match newline characters in multi-line text samples.
The m flag changes ^ and $ boundaries so that they operate per line rather than across the full input string.

What are the flag toggles for?+

They control how the pattern matches text: g finds all matches, i ignores case, m handles multiline anchors, and s allows dot to match newlines.

Why do capture groups matter?+

Capture groups reveal the exact subparts matched by a pattern, which is critical for parsing URLs, dates, and structured values.

Is this a full JavaScript regex engine?+

Yes. It uses the browser's native RegExp engine, so your testing behavior matches real JavaScript runtime behavior as closely as possible.