Regex Tester
Test and debug regular expressions
Use Regex Tester
Active sample: Email finder. Run the test to inspect positions, captures, and replacement behavior.
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Assumptions
Use Regex Tester for asset and page setup work when you need a local browser check and output you can review before using it in the next step.
Worked example
When To Use Regex Tester
- Paste a real example into Regex Tester that includes the edge case you need to check.
- Review whether the output matches prepare browser-facing assets or snippets for real pages before using it in the next step.
Sample Input And Output Checks
- Start with a sample that includes the failure you are trying to reproduce, not only a clean placeholder.
- Review rendering assumptions, minification side effects, and metadata completeness before trusting the output.
- Preview one real page or asset after generation so layout or metadata issues surface before release.
About This Tool
Practical Example And Review Checks
Test ^(INFO|WARN|ERROR)\s+\[(?<service>[^\]]+)\]\s+(?<message>.+)$ against several real log lines.
Review full matches, named groups, and unmatched lines before moving the pattern into code or a log filter.
- Compare before and after text when the regex is used for cleanup.
- Count matched text if excerpts or limits matter.
- Testing only one clean sample while production text includes blank lines.
- Using broad greedy patterns where a narrower character class is clearer.
- Forgetting that JavaScript regex syntax differs from PCRE features in some tools.
- The tester previews JavaScript-style regular expressions; it does not prove performance on every possible input.
- Final validation rules still belong in the target application.
Local processing note: Pattern tests run locally, but pasted logs can contain IDs, emails, or tokens that should be redacted before sharing.
Use the regex tester to build and debug JavaScript regular expressions against realistic text before moving a pattern into validation, scraping, log parsing, routing, or replacement code. The workbench shows match counts, positions, capture groups, flags, and replacement output.
How to Test Safely
Start with the smallest pattern that proves the case, then add anchors, groups, and flags one at a time. Test both matching and non-matching examples, especially empty strings, multiline input, punctuation, Unicode text, and values that should fail validation.
Interpreting Results
Capture groups show what your code can reuse, while match indexes show where extraction will happen. A pattern that works here follows the browser JavaScript regex engine; other languages may differ in lookbehind support, named groups, Unicode handling, or replacement syntax.
Common Pitfalls
Watch for overly broad .* matches, missing anchors in input validation, greedy groups that swallow too much text, and patterns that pass a single happy-path sample but fail real logs or form data. Compare replacement output with the Diff Checker before applying it to larger text.