Free Alternative to Regex101
Regex101 is the gold standard for regex debugging — but it sends your patterns and test strings to their servers for explanation generation. Irreva's Regex Tester runs entirely in the browser using JavaScript's native RegExp engine.
Features comparison
| Feature | Irreva | Regex101 |
|---|---|---|
| Live match highlighting | Yes | Yes |
| Capture group display | Yes | Yes |
| Multiple flags (g, i, m, s) | Yes | Yes |
| Regex engine | JavaScript (RegExp) | PCRE, Python, JS, Go |
| Explanation panel | No | Yes (AI-powered) |
| Processing | 100% browser | Server-side for explanation |
When Irreva is the right choice
For frontend JavaScript developers testing patterns that will run in the browser, Irreva's native RegExp engine guarantees identical behavior to production. Sensitive test strings (emails, SSNs, API keys) never leave your browser.
When Regex101 is better
For PCRE (PHP, Perl), Python re, or Golang regexp patterns, Regex101 supports those engines natively. If you need the detailed explanation panel, Regex101 remains the best choice.
Frequently Asked Questions
Does Irreva support lookaheads and lookbehinds?
Yes — modern JavaScript (ES2018+) supports lookbehind assertions, which are supported in Irreva's regex tester.
Are my test strings private?
Yes. Matching runs in your browser using the native RegExp object. Test strings are never sent to any server.