MintCloseAuthority (extension)

What it is

MintCloseAuthority names an address allowed to close the mint account itself and recover the rent-exempt lamports locked in it — provided the mint’s supply is zero. It’s a small extension that fixes a long-standing SPL Token annoyance: a created-then-abandoned mint locked its rent forever.

Why it exists

In SPL Token, a Mint account can never be closed. Every test mint, every mistaken deployment, every wound-down token left ~0.0015 SOL of rent stranded permanently. Token-2022 lets a designated authority close a fully-burned mint and reclaim that rent, which matters at scale for issuers who spin up and retire many mints.

Byte layout

This is the payload of a MintCloseAuthority TLV entry (extension_type = 3, length = 32). The full on-chain entry adds the 4-byte TLV header (see the TLV layout primer).

Total payload: 32 bytes.

Where you see it

Issuers that programmatically create and retire mints (test environments, ephemeral campaign tokens, factory-style token launchers). Most long-lived tokens leave this as None.

Common gotchas

• Supply must be zero to close. The program rejects CloseAccount on a mint with any outstanding supply. Every token must be burned first; otherwise the close fails and the rent stays locked.
• Closing the mint is permanent and frees the address. After close, the account is gone and its address could in principle be reused by a new account. Don’t cache a closed mint’s metadata as if the address is stable.
• It’s a separate authority from mint/freeze authority. The close authority can be a different key than the mint authority or freeze authority. Don’t assume one key holds all three.
• None at creation is forever. Like other mint extensions, if the mint shipped without a close authority it can never gain one — the rent is locked for good, exactly as in SPL Token.