Regex Complexity Calculator
Score regex complexity and flag ReDoS (catastrophic backtracking) risk. Enter your values, click Calculate, and get the full result with its breakdown — everything is processed on your device, nothing is sent to a server.
All calculations run in your browser. Your data is never sent to our servers.
Example
Example Input
(a+)+b
Example Output
high — ReDoS risk
How to Use
- 1Fill in each input field with the values you want to compute.
- 2If there are choices (units, mode, operation), pick what you need.
- 3Click the Calculate button (or press Ctrl+Enter).
- 4The main result and its breakdown appear in the Result area. Click Copy to copy it.
About the Regex Complexity Calculator
The Regex Complexity Calculator scores a regex pattern's complexity based on quantifier count, nested quantifiers, backreferences, and lookarounds. Most importantly, it flags nested quantifiers that risk ReDoS — patterns that can hang a regex engine on certain inputs.
Useful for security audits and avoiding regex denial-of-service vulnerabilities.
FAQ
Is this Regex Complexity Calculator accurate?
Yes. It uses standard formulas and runs directly in your browser at full JavaScript precision (plus BigInt/decimal.js for large numbers where needed).
Is my data sent to a server?
No. All calculations happen entirely on your device. No values are sent to or stored on our servers.