Developer & Text · Regex Tester
Test a regular expression and see every match
Quick answer
Open Toolfox → Regex Tester, paste test text and type your pattern in Options to see every match with its position and captured groups, updated as you type. Patterns use Rust regex syntax, which has no look-ahead, look-behind or backreferences. It runs entirely on your computer (Mac, Windows or Linux). Files are never uploaded.
How to do it
- Open Regex Tester and paste test text or open a file.
- Type the pattern in Options. Named groups use (?P<name>…) or (?<name>…).
- Toggle ignore case (i), multiline (m), dot matches line breaks (s) or whole words only.
- Review the matches and groups, then Copy or Save… them.
Options you can set
- Pattern
- Ignore case (i)
- ^ and $ match at line breaks (m)
- . matches line breaks (s)
- Whole words only
Good to know
- Uses Rust regex syntax, which always runs in linear time. Look-ahead, look-behind and backreferences aren't available.
- The first 1,000 matches are listed; the total count is always exact.
- Byte positions count UTF-8 bytes; character positions and columns count Unicode characters, starting at 0 and 1 respectively.
Regex Tester FAQ
Is it the same as JavaScript or PCRE regex?
Not exactly. It uses Rust regex syntax: look-ahead, look-behind and backreferences aren't available, and in exchange matching always runs in linear time.
Is there a limit on matches?
The first 1,000 matches are listed; the total count is always exact.
How are positions counted?
Byte positions count UTF-8 bytes. Character positions count Unicode characters starting at 0, and columns start at 1.
Is Regex Tester in Toolfox free?
Yes. Regex Tester is one of 57 tools in Toolfox, a free app for Mac, Windows and Linux with no account, ads, limits or watermarks.
Does Regex Tester upload my files?
No. Toolfox processes files on your own computer and works offline; your files are never uploaded.
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Updated 2026-10-18 · Toolfox v0.2.1