Free OTP Generator
Generate cryptographically secure one-time passwords for testing and development. Choose length, encoding type, and how many codes you need — all generated client-side, nothing stored.
6
Generated using crypto.getRandomValues() — cryptographically secure randomness. Safe for testing and development.
OTP Entropy Reference
| Length | Numeric (10 chars) | Alphanumeric (32 chars) |
|---|---|---|
| 4 chars | 10,000 possibilities | 1,048,576 possibilities |
| 6 chars | 1,000,000 possibilities | 1,073,741,824 possibilities |
| 8 chars | 100,000,000 possibilities | 1,099,511,627,776 possibilities |
| 10 chars | 10,000,000,000 possibilities | 1,125,899,906,842,624 possibilities |
| 12 chars | 1,000,000,000,000 possibilities | 1,152,921,504,606,847,000 possibilities |
✦ NumberOTP
Need to test OTP delivery with a real phone number?
NumberOTP gives you real virtual numbers in 150+ countries. Perfect for end-to-end testing of your OTP flow — receive live SMS codes in your dashboard or via API.
$0.10 free credits on signup · No card required · Numbers from $0.01
Frequently Asked Questions
Is this OTP generator cryptographically secure?
Yes. Every code is generated using window.crypto.getRandomValues() — the Web Cryptography API built into all modern browsers. This uses the operating system's CSPRNG (cryptographically secure pseudo-random number generator), the same source used by password managers and security keys.
What length should I use for OTP codes?
6 digits is the industry standard for most consumer apps (WhatsApp, Google, banks). 4 digits is common for PIN-style codes. 8–12 digit or alphanumeric codes are used for higher-security scenarios like account recovery tokens. Longer codes are harder to guess but harder to type.
Can I use these codes in production?
This tool is designed for development and testing. For production OTP systems, generate codes server-side, store only a hashed version, enforce a short expiry (5–10 minutes), and rate-limit attempts. Never send real OTP codes through client-side code.
What is the difference between numeric and alphanumeric OTPs?
Numeric OTPs (0–9) are easier for users to type on mobile keyboards and are standard in most SMS verification flows. Alphanumeric OTPs use A–Z and 0–9, providing far more entropy per character — a 6-character alphanumeric code has ~36^6 = 2.18 billion possibilities vs 10^6 = 1 million for numeric.
Why does my app need OTP verification instead of passwords?
OTP verification proves ownership of a phone number or email at the point of action. It is far more resistant to credential stuffing and phishing than static passwords because each code expires within minutes and is useless after first use.
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