BIP 342 (Tapscript)

BIP 342, known as Tapscript, is the Bitcoin improvement proposal that defines the script validation rules used when spending Taproot outputs. It activated together with BIP 340 (Schnorr signatures) and BIP 341 (Taproot) at block 709,632 in November 2021, and it applies to scripts committed under Taproot leaf version 0xc0.

Why it matters

Tapscript modernizes Bitcoin's scripting system without disturbing older transaction types. It replaces the legacy OP_CHECKMULTISIG opcode with OP_CHECKSIGADD, which counts valid signatures in a way that works efficiently with batch verification of Schnorr signatures. It also lifts the 10,000 byte script size limit and the 201 opcode limit for Tapscript spends, and it reserves a set of OP_SUCCESS opcodes that make future soft fork upgrades cleaner to deploy.

For users, the practical result is that complex spending conditions, such as multisignature arrangements or timelocked recovery paths, can be built with smaller on-chain footprints and better privacy than earlier script formats allowed.

How it works

Under BIP 341, a Taproot output commits to a Merkle tree of alternative spending scripts. When a spender reveals one leaf of that tree, BIP 342 defines how nodes evaluate the revealed script. Signature opcodes verify 64 byte Schnorr signatures, public keys are versioned so new signature schemes can be added later, and unspent code paths stay hidden. Only the executed branch ever touches the blockchain, which keeps fees lower and reveals the minimum necessary information.