Introduction
The Regex Tester runs your pattern against real sample text so you can tune flags and catch bad matches before production. Regex mistakes often come from missing anchors, accidental partial matches, or slow backtracking on large inputs. Test with edge cases, then copy the pattern into your code alongside automated checks. Use ^ and $ when the entire string must validate. Engines differ—confirm features for JavaScript, Java, or PCRE as needed. For readability, pair with the Regex Explainer. A small set of pass and fail examples beats a clever pattern with no tests.
Explore more in Tools, All Tools, or the Text Tools category.
How to use
- Write your pattern and flags (g, i, m, etc.).
- Paste representative text including edge cases.
- Inspect matches and capture groups in the UI.
- Adjust the pattern until validation matches your intent.
- Copy the final pattern into code and add automated tests.
Use cases
- Validate emails, slugs, and IDs with anchored patterns
- Extract fields from logs using capture groups
- Debug multiline matches with correct m-flag behavior
- Compare two approaches before choosing a regex for production
- Share a pattern with a teammate using a reproducible sample string
FAQ
- Why does my regex match part of the string?
- Without anchors, many patterns match substrings. Use ^ and $ for full-string validation.
- What causes slow regex?
- Nested quantifiers and ambiguous alternation can cause catastrophic backtracking. Prefer simpler patterns.
- Are lookarounds supported everywhere?
- Support depends on the engine. Test your target runtime’s flavor.
- How do I debug a complex regex?
- Use the Regex Explainer and break the pattern into smaller pieces.
- Is this tool free?
- Yes. DevToolDock provides this regex tester for free in your browser.