Regex Tester

About Regular Expressions

Global (g) - Find all matches instead of stopping at the first one.

Case Insensitive (i) - Match uppercase and lowercase letters equally.

Multiline (m) - ^ and $ match start/end of each line, not just the string.

Dotall (s) - Dot (.) matches newline characters as well.

Privacy

All processing happens locally in your browser. Your data is never uploaded to any server.

Frequently Asked Questions

What is a regular expression?

A regular expression (regex) is a sequence of characters that defines a search pattern. It's used for pattern matching within strings, such as finding emails, phone numbers, or validating input formats.

What are capture groups?

Capture groups are portions of the regex pattern enclosed in parentheses (). They let you extract specific parts of a match. For example, in the pattern (\d{4})-(\d{2})-(\d{2}), each group captures year, month, and day separately.

What's the difference between * and + quantifiers?

* matches zero or more occurrences (optional), while + matches one or more occurrences (at least one required). For example, a* matches "", "a", "aa", but a+ only matches "a", "aa", not empty string.

How do I match special characters literally?

Escape special characters with a backslash (\). For example, to match a literal dot, use \. instead of . which matches any character. Special characters include: . * + ? ^ $ { } [ ] \ | ( )

Is my data safe using this tool?

Yes, 100% safe. All regex testing happens locally in your browser using JavaScript. Your patterns and test strings are never sent to any server - we literally cannot see your data.

About Regex Tester

Test regular expressions online free with FreeToolBox's Regex Tester — write your regex pattern, input test strings, and instantly see all matches highlighted in real time. Regular expressions are a powerful text processing tool used by developers and data analysts to search, validate, and extract text patterns. Whether you're matching email addresses, validating phone number formats, parsing log files, or writing find-and-replace patterns, our Regex Tester helps you build and debug patterns interactively.

The tester runs entirely in your browser using JavaScript's built-in RegExp engine — no data is sent to any server. Supports flags: global (g), case-insensitive (i), multiline (m), and dotall (s). Shows all match groups and capture groups clearly. Completely free, no account required.

Frequently Asked Questions

What regex flavor does the tester use?

The tester uses JavaScript's ECMAScript (ES2018+) regex engine, which supports lookahead, lookbehind, named capture groups, and Unicode property escapes. Note that PCRE, Python, and Java regex flavors have some syntax differences.

How do I test multiline patterns?

Enable the multiline (m) flag to make ^ and $ match the start and end of each line rather than the entire string. Use the dotall (s) flag to make . match newline characters.

Can I see what each capture group matched?

Yes. The tester displays all match details including the full match, indexed capture groups ($1, $2, ...), and named capture groups (?<name>) so you can verify each part independently.

Is my regex data sent to a server?

No. All matching runs in your browser's JavaScript engine. Neither your patterns nor your test text are transmitted anywhere.

Regular Expression

Test String

Match Result

Capture Groups

Common Patterns

About Regular Expressions

Privacy

Frequently Asked Questions

Related Tools

About Regex Tester

Frequently Asked Questions