What the regex visualizer shows
Type a regular expression and test string and see every match highlighted in color, in real time, with ready-made presets for email, IP address, URL, phone number, and hex color. Instead of guessing whether a pattern matches, you watch exactly what it captures.
How regular expressions work
A regex is a tiny pattern language. Character classes (\d,
[a-z]) match sets of characters; quantifiers (*,
+, 4) control how many; anchors
(^, $) pin matches to the start or end; and
groups (( )) capture pieces for reuse. The engine scans the
string left to right, trying to satisfy the pattern at each position.
Why it matters
Regex shows up everywhere — form validation, log parsing, search-and-replace, routing. A visual tester turns the usual trial-and-error into something you can actually see and reason about. Keep common patterns handy with the regex cheatsheet.
Frequently asked questions
What's the difference between greedy and lazy quantifiers?
Greedy (.*) matches as much as possible then backtracks; lazy (.*?) matches as little as possible. Lazy is what you usually want when extracting content between delimiters.
What is a capture group?
Parentheses that remember the matched text so you can reference it ($1) in a replacement or extract it programmatically. Use (?: ) for grouping without capturing.
Why is my regex extremely slow?
Usually "catastrophic backtracking" — nested quantifiers on overlapping patterns (like (a+)+) can explode exponentially on non-matching input. Simplify the pattern or make quantifiers possessive/atomic.