Regex Tester for JavaScript Regular Expressions
Test patterns against sample text, tune flags, inspect match indexes, and copy results with browser-side processing.
Try a common regex task
Regex safety note
This tester uses JavaScript RegExp behavior. Check edge cases before using a pattern for validation, security filtering, or production data cleanup.
Index 8
Index 30
A regex tester runs a regular expression against sample text and shows matching results.
This page uses the browser JavaScript RegExp engine, so behavior follows JavaScript regex rules.
Use realistic sample text
Test against real-looking logs, URLs, IDs, or messages instead of only one idealized example.
Check edge cases
Include empty values, repeated matches, punctuation, line breaks, and mixed capitalization.
Example
Paste log text and test an email, ID, or URL pattern before moving it into code.
Assumption
Regex behavior follows browser JavaScript rules and supported flags.
Limitation
It does not emulate regex engines from Python, PCRE, Java, or databases.
Testing only one idealized sample
Add misses, edge cases, punctuation, line breaks, and mixed case before trusting the pattern.
Forgetting engine differences
This tester uses JavaScript RegExp. PCRE, Python, Java, database, and shell regex behavior can differ.
Creating expensive patterns
Nested quantifiers and broad wildcards can become slow on long text. Test realistic input sizes.
Log parsing
Test patterns for timestamps, IDs, error codes, and repeated log lines.
Form validation
Check JavaScript patterns for emails, slugs, usernames, and simple inputs.
Capture groups
Confirm that groups capture the intended pieces before using match results.
Search cleanup
Find repeated words, delimiters, URLs, or structured snippets in pasted text.
Does it support flags?
Yes. Use JavaScript flags such as g, i, m, s, u, v, y, and d when supported by the browser.
Which regex engine does it use?
It uses the browser JavaScript RegExp engine. Regex engines vary, so results can differ from PCRE, Python, Java, database, or shell behavior.
Can it show capture groups?
Yes. When a match includes capture groups, the result notes the group count.
How is regex testing processed?
Pattern testing is handled in the browser for this tool based on the current public implementation.
Suggested workflow
Pattern cleanup path
Clean sample text, test a JavaScript regex, and compare before-and-after results.