Nostr keys come in two formats: hex and bech32.

Hex is the raw format: 64 characters using 0-9 and a-f. This is what the cryptography actually uses. Bech32 is the human-readable format that starts with npub for public keys and nsec for private keys, and includes a checksum to catch typos. An npub1abc... is the same key as a 64-character hex string, just encoded differently.

Use bech32 when sharing or storing keys since the prefix makes it obvious what you're looking at and the checksum prevents errors. Use hex when interfacing with low-level tools or libraries that expect it. Most apps accept both, and Signet accepts both.