mint authority is active, someone can mint more of the token at any time — supply is not capped. If it's revoked (null), the current supply is permanent. The same logic applies to freeze authority: an active value means the issuer can freeze any holder's account.getAccountInfo RPC call, server-side, with a 5-minute cache. Mint state changes rarely, so even popular tokens hit the upstream RPC at most a handful of times per hour regardless of traffic.On-chain SPL mints store decimals, supply, and authorities — but not name or symbol. Those live in a separate Metaplex Metadata account. Reading them requires deriving a program-derived address (PDA), which needs ed25519 math beyond this page's scope.
The address allowed to mint new tokens into circulation. If it's null, the supply is permanently capped — minting is disabled. Stablecoins typically keep mint authority active; capped tokens like fixed-supply NFTs revoke it.
The address allowed to freeze any token account holding this mint, blocking transfers. Most user-facing tokens have it null. USDC and USDT keep it active for compliance reasons.
Token-2022 is a newer program with optional extensions (transfer fees, confidential transfers, interest bearing tokens, etc.). It's a superset of SPL Token — most simple tokens still use the original program for compatibility.