it3 — Free URL Shortener

Regex Tester

Experiment with patterns and flags against sample strings. See matches with indexes and try a replacement string.

Flags

Uses String.replace. With flag g, all matches are replaced.

FAQ

Flavors matter?

This uses JavaScript `RegExp`—PCRE lookahead or backreference rules differ from grep or Ruby; confirm engine when porting patterns.

Catastrophic backtracking?

Nested quantifiers like `(a+)+$` can freeze the tab; keep alternation tight and test with short strings first.

Unicode property escapes?

Require `u` flag and ES2018+ support—Safari versions vary; verify target matrix.

Replacement callbacks?

We only show simple string replacement—`$1` groups work but function replacers are out of scope here.

Security?

Never run user-supplied regex on servers without sandboxing—ReDoS is real.

Performance on huge haystacks?

Megabyte logs belong in ripgrep, not interactive browsers.

🆓100% Free
🔒Secure & Private
⚡No Signup Needed
Share:WhatsAppTwitterLinkedInTelegram
❓

Frequently Asked Questionsabout Regex Tester

Regex Tester is a free browser-based utility on it3.site. Use it when you need fast results without installing desktop software. It is designed for quick daily workflows like content cleanup, format conversion, or validation before publishing.
Yes. Regex Tester is free to use. Most processing in it3 tools runs directly in your browser, which helps keep your input private and reduces server dependency.
You provide input, the tool applies client-side logic in JavaScript, and the processed output is shown instantly. For many tools, data is transformed in-memory and cleared when you close or refresh the page.
A common use case is speeding up repetitive work before publishing or sharing: preparing cleaner data, generating developer-ready output, or validating content quality in seconds.
For large inputs, performance depends on your device and browser memory. Keep backups of original content, verify final output before production use, and test on real target environments when needed.
Browser tools are faster to open and easier to use across devices, while desktop apps may support larger batch workflows and advanced automation. For everyday quick tasks, the browser version is usually enough.
Still have questions?
We are here to help you get the most out of this tool.
Contact us →

Related Tools

Explore More Tools

Tap a tag to open a tool. The current page is highlighted.

File TransferCron Job SchedulerPassword GeneratorWhatsApp Link GeneratorRedirect CheckerUTM BuilderUnit ConverterWorld Time ConverterJSON FormatterXML FormatterBase64 Encoder / DecoderStringify to JSONJSON to StringifyURL Encoder DecoderSlug GeneratorText Case ConverterRemove Extra SpacesText ReverserSort LinesWord CounterCharacter CounterRandom Text GeneratorDiseImage CompressorImage ResizerJPG to PNG ConverterPNG to WebP ConverterWebP to JPG ConverterFavicon GeneratorScreenshot to PDFImage to Base64 ConverterImage Crop ToolPhoto Watermark ToolHTML Encoder / DecoderCSS MinifierJS MinifierHTML MinifierMorse Code TranslatorJSON ValidatorHTML BeautifierRegex Testerhtaccess Redirect GeneratorHTTP Headers CheckerQR Code GeneratorAge CalculatorXML Sitemap GeneratorRobots.txt GeneratorKeyword Density CheckerPercentage Calculator
Buy Me a Coffee at ko-fi.com