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Test and debug regular expressions with real-time match highlighting.
Use Regex Tester to try a regular expression pattern against realistic sample text before putting it into code, validation rules, or search filters. The preview helps you inspect matches, capturing groups, anchors, and flags. Test both strings that should match and strings that should not match so the pattern is neither too loose nor too strict.
Replace broad tokens with explicit character classes and use anchors such as ^ or $ when the whole line must match.
Review multiline and global flags because anchors and repeated searches behave differently with those options.
Add non-capturing groups with ?: for structure and reserve capturing parentheses for values you need.
Test smaller pieces, name the purpose in surrounding code, and keep sample strings that show accepted and rejected cases.
Regex Tester evaluates the pattern and sample text in your browser, so the examples are not intentionally uploaded to a remote matching service. Use sanitized logs and fake customer records because sample text can still reveal private identifiers during screen sharing or copy paste.
Include lines that should match plus near misses that should be rejected by the pattern.
Add anchors, character classes, quantifiers, and capturing groups that match the exact rule you need.
Check global, case-insensitive, or multiline behavior to mirror the JavaScript environment where the regex will run.
Confirm the highlighted matches and captured values before copying the pattern into code.
Pattern: ^ORD-[0-9]{6}$. Sample: ORD-123456 matches, while ORD-123 and XORD-123456 do not.
Pattern: ^(INFO|WARN|ERROR): (.+)$. Sample: ERROR: disk full captures ERROR as group 1 and disk full as group 2.
Pattern: ^[a-z0-9]+(?:-[a-z0-9]+)*$. Sample: image-resizer matches, while Image Resizer and image--resizer are rejected.
It applies your regular expression pattern to sample text and highlights matches so you can inspect groups, boundaries, and flag behavior before using the pattern in code.
Common flags include global matching, case-insensitive matching, and multiline behavior. Test the same flags your target JavaScript regex will use.
Use parentheses around the part you need to capture, then test against realistic sample lines. Name or document the groups in your code if other people will maintain the pattern.
A greedy quantifier such as .* may consume more than expected. Try a more specific character class, a lazy quantifier, or start and end anchors.
No. It helps with representative samples, but production text can contain unexpected line breaks, Unicode characters, or very long strings. Add tests in the destination codebase too.
Test the pattern as the target environment expects it. A JavaScript regex literal, a JSON string, and a form field can require different escaping, especially for backslashes, forward slashes, and replacement strings.
Add sample text that should not match, such as malformed IDs, extra characters, missing prefixes, or invalid dates. A useful regex test includes both accepted and rejected examples so a green match is meaningful.
Realistic text exposes spacing, punctuation, and line boundary problems that short invented samples often miss.