Test Regex Without Sending Your Data to a Server

Regular expressions are powerful and easy to get wrong. You tweak a pattern, re-run a test, repeat — often dozens of times. Online testers help, but your test corpus may include real customer emails, log lines, or production JSON.

The risk of upload-based testers

Some popular regex playgrounds transmit both pattern and subject to a remote service. That is convenient for sharing links — risky for sensitive strings.

ZeroKit's regex tester runs JavaScript RegExp locally. Your pattern and haystack stay in-tab.

Test privately → ZeroKit Regex Tester

What you get

• Live matching as you edit (depending on tool UX)
• Flags such as g, i, m, s where exposed in the UI
• Group capture visibility for debugging
• A curated list of starter patterns for email, URLs, hex colours, etc.

Regex cheat sheet

Token	Meaning
.	Any char (except newline by default)
\d	Digit
\w	Word char
\s	Whitespace
^ / $	Start / end
[abc]	Character class
(a|b)	Alternation
(group)	Capturing group
{n,m}	Repetition bounds

Example patterns

Use case	Starting point
Email (simple)	[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}
IPv4 (loose)	\b\d{1,3}(\.\d{1,3}){3}\b
Hex colour	# + 3- or 6-digit hex (build in regex tester)

Want English → regex? Try the AI Regex Builder.

Regex testing checklist

• Start with a small sample before testing a full log file.
• Turn on flags deliberately: g, i, m, and s change results.
• Test matching and non-matching examples.
• Check capture groups, not only the full match.
• Re-test the final pattern in the runtime that will execute it.

FAQ

Which regex flavour?›

The tool uses JavaScript regular expressions — good for browser and Node stacks, not identical to PCRE or every engine.

Production tip›

Always re-test critical patterns in the runtime that will execute them (Java, Go, Python, etc.) — edge cases differ.