Regex Generator (from Examples)
Generate a regex pattern from sample strings — paste what should match and what should not.
What is Regex Generator?
A regex inference tool that analyzes example strings to detect common patterns — literal prefixes/suffixes, digit runs, letter runs, separators — and synthesizes a regex that matches the positives while avoiding the negatives.
How it works
We align your examples character-by-character, detect which positions are constant vs variable, infer character classes for variable positions, and assemble the pattern with appropriate quantifiers.
- Enter your input. Type or paste your input into the field above — the tool responds instantly.
- Review the result. Output updates live as you type. Everything runs entirely in your browser.
- Copy or download. Use the Copy button to grab the result, or Download to save it as a file.
Examples
Reverse-engineering a pattern
Feed a few sample strings and get a regex that matches them — then test it against negatives to refine.
Common mistakes
Overfitting the samples
Generated patterns match the examples given, not necessarily the full domain — always test against edge cases.
Frequently asked questions
How accurate is the generated regex?
It's a best-guess from your examples. The more examples you provide, the better the pattern will be. Always test the generated regex before using it in production.