Regex Tester
Test regular expressions against sample input with live match highlighting. Use this free online tool directly in your browser.
Flags
Test String
Replacement (optional — use $1, $2 for groups, $& for full match)
What is Regex Tester?
Regular expressions (regex) are a powerful pattern-matching language built into virtually every programming language. They allow you to find, validate, extract, and transform text using compact pattern syntax. A regex pattern describes the structure of strings you want to match — characters, repetitions, groups, anchors, and lookaheads combine to match everything from email addresses to log file entries. This tester shows live match highlighting as you type, supports all standard JavaScript flags (g, i, m, s, u), displays capture groups, and lets you test your pattern against real sample input before adding it to production code. Since regex syntax differences exist between languages, always verify your pattern in the target runtime.
How to use
- 1
Paste or enter your data in the Regex Tester input area.
- 2
Run the conversion, generation, or validation action.
- 3
Copy or download the result for your project workflow.
Common Use Cases
- 1
Build and test email, phone, or URL validation patterns before adding them to form validation logic
- 2
Construct capture groups to extract structured fields from server log lines
- 3
Debug why a regex works in the browser console but fails in your Python or Go backend
- 4
Test edge cases against real sample data to verify your pattern handles them correctly
- 5
Quickly prototype replacement patterns for string transformation without spinning up a REPL
Try an Example
Example Input
Pattern: ^[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}$
Text: help@bitesizetools.comFrequently Asked Questions
What is Regex Tester?
Regex Tester is a free browser-based utility on Bite Size Tools. Test regular expressions against sample input with live match highlighting.
Is Regex Tester safe to use with sensitive data?
Yes. Tool processing runs in your browser, so your input is not sent to a server by default in this app.
Can I use Regex Tester for production work?
Yes. You can use the output directly in development and production workflows after validating it with your project requirements.