Regex Tester

About the Regex Tester

Regex Tester tests, debugs, and evaluates Regular Expressions against sample text in real time, highlighting matching groups, supporting all standard flags (`g`, `i`, `m`, `s`, `u`), and explaining pattern tokens.

How to Use the Regex Tester

1. Enter your Regular Expression pattern (e.g. `^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$`).
2. Select flags: Global (`g`), Case-Insensitive (`i`), Multiline (`m`), DotAll (`s`).
3. Paste test text into the test area.
4. Review color-coded match highlights, capture group breakdowns, and match counts.

Expert Tips for Regex Tester

• Capture Group Inspection: View individual named and numbered capture groups for each match index.
• Regex Cheat Sheet: Use built-in token cheat sheets for character classes, lookaheads `(?=...)`, and quantifiers.
• Catastrophic Backtracking Prevention: Test patterns against complex text to prevent ReDoS CPU freezes in production.

Related Guides & Tutorials

• Json Formatting For Developers — Learn in-depth concepts, best practices, and expert tips.
• Base64 Encoding Explained — Learn in-depth concepts, best practices, and expert tips.

Frequently Asked Questions

Which regex flavor does this use?

Standard JavaScript regex syntax, which should also work in most other languages with minor differences.

What does the 'g' flag do?

The global flag finds all matches in the string rather than stopping after the first one — without it, only the first match would be found and highlighted.

What's the difference between 'i' and 'm' flags?

The 'i' flag makes matching case-insensitive, while the 'm' flag changes how ^ and $ behave, making them match the start and end of each line rather than just the start and end of the whole string.

Can I use this to build a regex for our AI Regex Generator's output?

Yes — it's a great way to verify and refine a regex pattern generated elsewhere, testing it against your own real sample strings before using it in actual code.

Can I test multiple patterns against the same string?

Yes — simply update the pattern field and the highlighting refreshes instantly against your existing test string, making it easy to compare several pattern variations quickly.

Cite This Tool

Referencing this tool in a paper, article, or bibliography? Copy a ready-made citation below.

NexLove.org. (2026). Regex Tester [Software]. https://nexlove.org/tools/regex-tester.html

“Regex Tester.” NexLove.org, 2026, nexlove.org/tools/regex-tester.html.

NexLove.org (2026) Regex Tester. Available at: https://nexlove.org/tools/regex-tester.html (Accessed: 2026).

@misc{nexlove_regex_tester,
  title = {Regex Tester},
  author = {{NexLove.org}},
  year = {2026},
  url = {https://nexlove.org/tools/regex-tester.html}
}

Embed This Tool

Add the live Regex Tester tool to your own website with this snippet — it loads the real, working tool in an iframe, not a static screenshot.

<iframe src="https://nexlove.org/embed/regex-tester.html" width="100%" height="600" style="border:1px solid #e2e8f0;border-radius:12px" title="Regex Tester — NexLove.org" loading="lazy"></iframe>