SPL Token Instructions

What it is

The SPL Token Program’s instructions move and manage token balances: transfer, mint, burn, approve a delegate, freeze, close. They operate on Mint and Token Account accounts. Token-2022 shares the same instruction layout plus extension-specific additions.

Why it exists

Every token action — sending USDC, minting an NFT, burning a supply, approving a DEX to spend — is one of these instructions. They’re among the most-executed instructions on Solana.

Byte layout

SPL Token instruction data uses a 1-byte discriminator followed by the variant’s fields:

Transfer is bytes 03 + an 8-byte little-endian amount. TransferChecked adds a decimals byte and requires the mint as an account so the program can verify the caller’s decimals assumption.

Where you see it

Every token movement on Solana. Wallet sends, DEX swaps (which approve + transfer), mint operations, and supply burns all decode to these.

Common gotchas

• Prefer the Checked variants. Transfer (3) doesn’t verify decimals, so a client using the wrong decimals can move 1000× the intended amount. TransferChecked (12) passes the mint and decimals so the program rejects a mismatch. New code should use Checked.
• amount is atomic units, not display units. Transferring “1 USDC” (6 decimals) is amount = 1_000_000. The instruction never sees the human number.
• 1-byte discriminator, unlike the 4-byte native programs. SPL Token, SPL Associated Token Account, and most SPL programs use a single-byte tag.
• Authority comes from accounts, not data. Who’s allowed to transfer (owner or delegate) is determined by which account signs, not by the instruction data. The data is just the discriminator + amount.