Why does my regex work here but not in my code?

Different programming languages have slightly different regex flavors. This tool uses JavaScript regex. If you are writing Python or Java, check for differences in lookbehind support, named groups or flag syntax.

Can I use lookaheads and lookbehinds?

Yes. The tool supports lookaheads (?=...) and (?!...) as well as lookbehinds (?<=...) and (?<!...) in modern browsers that support ES2018 regex features.

Regex Tester in Your Browser

Debug regular expressions without installing IDE plugins or CLI tools. This browser-based regex tester highlights matches in real time as you type, making it easy to iterate on complex patterns and understand how they work.

Open Regex Tester

Steps to Test a Regex

Enter your regular expression pattern in the pattern field
Set flags like global (g), case-insensitive (i), or multiline (m)
Paste your test string in the input area
View highlighted matches and capture group details instantly

Common Use Cases

Prototyping regex for input validation in web forms
Debugging patterns that work in one language but fail in another
Extracting structured data from unstructured text
Verifying regex before adding it to production code

Frequently Asked Questions

Why does my regex work here but not in my code?: Different programming languages have slightly different regex flavors. This tool uses JavaScript regex. If you are writing Python or Java, check for differences in lookbehind support, named groups or flag syntax.
Can I use lookaheads and lookbehinds?: Yes. The tool supports lookaheads (?=...) and (?!...) as well as lookbehinds (?<=...) and (?<!...) in modern browsers that support ES2018 regex features.