What is Regex?
Regex is a pattern language used to find, validate, extract and replace parts of text. It appears in editors, programming languages, logs, technical SEO, automation and data pipelines.
Premium tool for developers
Regex Tester
Write, test and refine regular expressions in real time with visual highlights, flags, replace preview, captured groups, practical examples and a cheatsheet. Everything runs locally in your browser.
Client-side: your regex and test text are not sent to the server.
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Ready to test regex.
How to test a regular expression
- Type the regex pattern, choose flags and paste real test text.
- Review the highlight, match list, captured groups and positions.
- Use replace, ready examples and the cheatsheet to refine the pattern safely.
How Regex works
A regular expression combines literal characters, classes, groups, quantifiers and anchors. The engine scans the text for fragments that satisfy the pattern and returns matches, indexes and captured groups.
Practical examples
Regex helps find emails, URLs, CPFs, ZIP codes, IPs, dates, phone numbers, HTML tags and hashtags. The ready examples on this page cover common development and analysis tasks.
Regex for validation
For validation, regex is good at format checks. For business rules, check digits or data semantics, combine regex with specific backend or application validation.
Regex for programming
Developers use regex for light parsing, string cleanup, data transformation, tests, simple routing, filters, imports and log processing.
Regex in JavaScript
This tool uses the native JavaScript regex engine in your browser. Flags like g, i, m, s, u and y follow RegExp behavior, including replace with $&, $1 and captured groups.
Common Regex mistakes
Common mistakes include escaping special characters incorrectly, forgetting the global flag, using unnecessary groups, creating overly greedy patterns and trying to solve complex rules only with regex.
When to avoid Regex
Avoid regex for complex HTML, nested languages, highly contextual rules or critical validation that requires calculation. Dedicated parsers and validators are safer in those cases.
Frequently asked questions
Is the test text sent to the server?
No. Testing, highlighting, replace and history happen locally in the browser.
Which regex engine does this tester use?
It uses the browser native JavaScript RegExp engine.
Can I inspect captured groups?
Yes. The tool lists matches, positions and numbered or named captured groups when available.
Can regex truly validate CPF?
Regex validates the format. To validate CPF check digits, use a specific rule in addition to regex.
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