Common Regex workflows
Regex flavors share syntax but not behavior. Lookbehind, named groups, Unicode classes and backtracking differ between JavaScript, Python re and Go RE2. Test with the flavor your application runs and with input that should not match.
Test extraction and replacement
Choose the regex flavor used by your application, inspect groups and matches, then try replacement on representative input. Browser JavaScript, Python re and Go regexp have different syntax and behavior.
- Regex Tester — Test regexes with live highlighting and groups.
- Python Regex Tester — Test patterns with Python re syntax and semantics.
- Go Regex Tester — Test patterns with Go regexp (RE2) syntax and semantics.
- Find and Replace — Replace text in bulk, with optional regex.
Check a pattern against edge cases
Generate strings that a pattern accepts, then paste them alongside inputs that should fail. Review anchors and quantifiers when unexpected text matches.
- Regex Sample Generator — Generates repeatable examples from a JavaScript-style regex using a seed.
- Regex Tester — Test regexes with live highlighting and groups.
Choose the same regex flavor as your runtime
A pattern that works in JavaScript may fail in Python or Go. The flavor-specific testers document compatibility limits. Timeouts keep expensive matching from blocking the page, but do not prove a pattern is safe for production input.
Frequently asked questions
Which regex tester should I use?
Use the tester for the language that will run the pattern: JavaScript, Python re or Go regexp. Their syntax and matching behavior differ, so a pattern can work in one and fail in another.
Why does my pattern freeze other testers?
Nested quantifiers can cause catastrophic backtracking. The JavaScript tester stops runaway matching instead of freezing the page; rewrite the pattern before using it on untrusted input.
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