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Describe the pattern you want to match and get a regular expression back, with each component explained so you can verify it does what you meant rather than trusting it blindly.
Describe what you want to match in plain English and get a tested regex pattern with explanation. Browse 30+ pre-built patterns for common use cases like emails, URLs, dates, IPs, and more.
Always test a generated regex against inputs that should not match. A pattern that matches all your positive examples and also matches half your negative ones is worse than no pattern, and it is the standard failure mode: you check that it catches what you wanted and never check what else it catches.
Some things should not be regex at all. Email validation is the canonical example: the RFC-compliant pattern is famously monstrous, and the practical answer is to check for an @ with something on both sides and then send a confirmation email. Parsing HTML with regex is the other one. Nested structures are not a regular language and no pattern will handle them correctly.