Regex Tester & Visualizer
Test and debug regular expressions instantly in your browser. Visual highlighting, capture groups, and execution time. 100% private, no data uploaded.
- Real-time highlighting
- Capture group viewer
- No upload, no sign-up
Match Details
| # | Match | Index | Groups |
|---|---|---|---|
| 1 | support@tooldeck.online | 28 | - |
| 2 | sales@example.com | 55 | - |
- Runs in your browser
- No upload
- No sign-up
- Real-time matching
- Works offline
Related tools
Free AI and developer tools that run in your browser. Nothing uploaded, ever.
Why this tool is the best choice
Most regex testers are cluttered with ads or send your text to a server. This one is clean and private.
| Feature | TToolDeck | Regex101 | RegExr |
|---|---|---|---|
| Runs entirely in your browser | Yes | No | No |
| No data sent to a server | Yes | No | No |
| Live highlighting as you type | Yes | Yes | Partial |
| Execution time tracking | Yes | Yes | No |
| No ads or interruptions | Yes | No | No |
| Completely free | Yes | Yes | paid |
How it works
- 1
Enter your regex
Type your regular expression pattern and select the flags (g, i, m, s) you need.
- 2
Paste your text
Add the text you want to test. Matches are highlighted instantly as you type.
- 3
Analyze matches
View execution time, total matches, and the exact capture groups for every match.
Everything you get for free
Real-Time Highlighting
See exactly what your regex matches as you type. No need to click a "Run" button, the results update instantly.
Capture Group Viewer
If your regex uses groups (parentheses), we break them down into a clean table so you can verify your data extraction.
100% Secure
Regex tests often contain sensitive text like emails or logs. Because it runs locally, your data never leaves your device.
Performance Metrics
See exactly how many milliseconds your regex takes to execute. Spot catastrophic backtracking before it hits production.
Flag Controls
Easily toggle Global (g), Case Insensitive (i), Multiline (m), and DotAll (s) flags with one click.
Clean Interface
No popups, no ads, and a dark mode that is easy on the eyes during long debugging sessions.
What people use it for
Validating Emails
Quickly test standard email regex patterns against real-world email formats to ensure they match correctly.
Parsing Logs
Extract IP addresses, timestamps, or error codes from raw server logs using capture groups.
URL Routing
Test your Next.js or Express URL routing patterns before writing the code.
Data Cleaning
Create regex patterns to find and remove unwanted characters, extra spaces, or HTML tags from text.
Learning Regex
Use the live highlighting and match groups to learn how regex engines parse different patterns visually.
Bug Hunting
Check execution time to ensure your complex regex isn't going to freeze the browser on a large block of text.
Questions people ask
What regex flavor does this use?
This tool uses the native JavaScript RegExp engine. It supports standard ECMAScript regular expressions, which are highly compatible with other languages.
Is my text sent to a server?
No. The matching process is handled entirely by your browser's JavaScript engine. Your text and regex patterns are never uploaded or logged.
What are the flags (g, i, m, s)?
g (Global) finds all matches instead of stopping at the first. i (Insensitive) ignores case. m (Multiline) makes ^ and $ match the start/end of lines. s (DotAll) makes the dot match newlines.
Why does it say "Invalid Regex"?
If you have an unclosed parenthesis, an unmatched bracket, or an invalid quantifier, the JS engine throws an error. The tool will show you exactly what is wrong.
Why is the execution time important?
Some regex patterns suffer from "catastrophic backtracking," which can freeze your computer. Tracking the execution time helps you write efficient regular expressions.
Does it support lookbehinds?
Yes, modern browsers (Chrome, Edge, Safari) fully support positive and negative lookbehinds (?<=) and (?<!).
Can I test multiple lines of text?
Yes. Paste multi-line text into the test string box and use the "m" (Multiline) flag if you want ^ and $ to match line boundaries.
Is there a character limit?
No. Because it runs entirely in your browser, the limit is only your device's memory.