Free RegEx Negative Lookahead Tester & Visualizer

Debug, test, and visualize negative lookahead assertions `(?!...)` in real-time.

Regular Expression

/ /g

Invalid Regex

Test String

Visualization

Matches found: 0

How Negative Lookahead Works

A Negative Lookahead (?!...) asserts that the pattern inside the parentheses does not follow the current position.

It is a non-consuming assertion, meaning it checks the condition but does not include the check in the final match length.

Example: \b\w+(?!ing)\b

This matches any whole word that is not followed by "ing".

Type your RegEx in the top box.
Type your test text in the middle box.
Matches will be highlighted in yellow.
The tool updates instantly as you type.