Pattern and flags
Enter the pattern without slash delimiters and choose JavaScript flags such as global, case-insensitive, multiline, dotAll, or Unicode as supported.
Developer Tools · Local processing
Regex Tester
Test JavaScript regular expressions, flags, matches, and capture groups with timeout protection.
Isolated worker
Regex Tester
Inputs and results stay in this page and are not sent to any server.
0 matches
No matches yet. The worker is terminated if execution exceeds 500 ms.
The practical guide
Inspect regex matches without letting a bad pattern freeze the main interface.
The tester runs the expression against sample text in a disposable Web Worker and reports matches and captured groups.
Matches and captures
Review each match location and any numbered or named capture groups returned by the JavaScript regex engine.
Timeout protection has limits
The worker is terminated after the safety window, reducing interface freezes. It does not prove that a pattern is safe for every production input.
Privacy by architecture
Your files and tool inputs stay in your browser.
The selected files, inputs, settings, and outputs are processed in this page and are not uploaded to any server.
Questions, answered
Frequently asked questions
Which regex syntax is used?
The browser JavaScript RegExp engine is used, so syntax and features follow that implementation.
Why did the test time out?
The expression may cause catastrophic backtracking or the input may be too expensive for the safety window.
Does the tester replace text?
No. It reports matches and groups; it does not currently provide a replacement workflow.
Can a passing test guarantee production safety?
No. Test representative worst-case inputs and apply limits in the system where the pattern will run.