.onion Link Validator — Check Onion URL Format
Validate the format of any .onion address. Checks v2 vs v3 format, length, character set, and common errors in onion URLs.
.onion Link Validator
Validate the format of a .onion address and check whether it uses v2 or v3 format.
Validation happens in real time as you type. Nothing is sent to any server.
How are .onion addresses generated?
V3 addresses (current): A v3 .onion address is derived from an ed25519 public key. The 56-character address encodes the public key (32 bytes), a checksum (2 bytes), and a version byte, all base32 encoded. This provides 256-bit security and makes it cryptographically infeasible to impersonate a service.
V2 addresses (deprecated): V2 addresses were derived from the SHA-1 hash of a 1024-bit RSA public key, truncated to 80 bits and base32 encoded into 16 characters. The shorter key length and weaker hash made them vulnerable to impersonation attacks.
- Only the operator of the corresponding private key can host the service
- The address itself acts as both an identifier and a verification mechanism
- Vanity addresses (with readable prefixes) are generated by brute-forcing key pairs until a match is found
- V3 addresses are significantly longer but provide much stronger security guarantees