Regex Tester Free Online Tool

Test your regular expressions against sample text. Free, no signup required. Use it right in your browser.

About this tool

What it does, limits, use cases, tips, and answers to common questions.

Overview

Regular expressions are easy to get almost right. This tester lets you paste a pattern and a sample string and see matches, groups, and failures before you ship the regex to production.

It uses JavaScript regex semantics. That is not identical to Python, grep, or .NET. Flags (i, m, g, s) change meaning. A pattern that "works" here can still ReDoS a server if it is catastrophic. Keep patterns simple.

Testing is local. You can paste log lines that contain IPs or emails without sending them to a hosted regex debugger.

Limitations

  • JavaScript regex is not PCRE or Python.

  • Catastrophic backtracking can freeze the tab. Avoid nested .* on huge inputs.

  • This is not a replacement for unit tests in your repo.

Common Use Cases

  • Validating emails or slugs before writing backend code.

  • Extracting IDs from log lines.

  • Teaching yourself lookaheads on a short example.

Pro Tips

  • Test against a string that should fail, not only one that should pass.

Frequently Asked Questions

Why no match?

Check flags, anchoring (^ $), and whether you need the global flag for multiple hits.

Can I save patterns?

Not in an account. Copy them into your codebase or a snippet file.

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