Blocks and Operations#

The content of a Tezos block is made up of a block header and a payload consisting of a list of operations.

This page first describes the protocol-specific part of the block header, and then explains what operations are. For the protocol-independent part of the block header, see Shell header.

Protocol-specific block header#

Recall that, for the shell to interact with the economic protocol, two notions are defined abstractly at the level of the shell and made concrete at the level of the consensus protocol. Namely, these two notions are the protocol-specific header and the fitness.

As in Emmy*, the protocol-specific header contains the fields:

  • signature: a digital signature of the shell and protocol headers (excluding the signature itself)

  • seed_nonce_hash: a commitment to a random number, used to generate entropy on the chain

  • proof_of_work_nonce: a nonce used to pass a low-difficulty proof-of-work for the block, as a spam prevention measure

  • liquidity_baking_toggle_vote: a vote to continue the Liquidity Baking Subsidy, stop it, or abstain.

There are two additional fields: payload_hash and payload_round which are needed for establishing if a block is final.


Operations implement and reify different functionalities provided by a Tezos economic protocol: from reaching consensus on the state of the Tezos blockchain, to performing smart contract calls and transactions. Each Tezos economic protocol can specify different kinds of operations.

This page only describes the operations supported by the economic protocol that implement enabled features – that is, those available to end-users on Tezos Mainnet. The complete list of operations, including those corresponding to features in development or available only on test networks, is given in the OCaml Documentation .

Validation Passes#

The different kinds of operations are grouped into classes. Each class has an associated index, a natural number, also known as a validation pass. There are currently four classes of operations: consensus, voting, anonymous, and manager operations. This order also specifies the validation and application priority of each of these classes. Consensus operations are considered the highest priority ones, and manager operations the lowest.

Each kind of operation belongs to exactly one validation pass, except for the Failing_noop operation which belongs to no validation pass and therefore cannot be applied.

In the sequel, we describe the different classes of operations, and the different kinds of operations belonging to each class.

Consensus Operations#

Consensus operations are administrative operations that are necessary to implement the consensus algorithm. There are two kinds of consensus operations, each belonging to the different voting phases required to agree on the next block.

  • A Preattestation operation implements a first vote for a candidate block with the aim of building a preattestation quorum.

  • An Attestation operation implements a vote for a candidate block for which a preattestation quorum certificate (PQC) has been observed.

Voting Operations#

Voting operations are operations related to the on-chain Tezos Amendment process. In this economic protocol, there are two voting operations:

  • The Proposal operation enables delegates to submit (also known as to “inject”) protocol amendment proposals, or to up-vote previously submitted proposals, during the Proposal period.

  • The Ballot operation enables delegates to participate in the Exploration and Promotion periods. Delegates use this operation to vote for (Yea), against (Nay), or to side with the majority (Pass), when examining a protocol amendment proposal.

Further details on each operation’s implementation and semantics are provided in the dedicated entry for on-chain governance.

Anonymous Operations#

This class groups all operations that do not require a signature from a Tezos account (with an exception, detailed below). They implement different functionalities of the protocol, and their common characteristic is that they allow the account originating these operations to remain anonymous in order to avoid censorship.

Two operations in this class implement functionality pertaining to the protocol’s random seeds generation mechanism:

  • The Seed_nonce_revelation operation allows a baker to anonymously reveal the nonce seed for the commitment it had included in a previously baked block (in the previous cycle).

  • The Vdf_revelation operation allows the submission of a solution to, and a proof of correctness of, the VDF challenge corresponding to the VDF revelation period of the randomness generation protocol.

Further details on the latter operation’s implementation and semantics are provided in the random seed generation protocol.

Three operations in this class are used to punish participants which engage in Byzantine behaviour – notably delegates which “double sign” blocks, or emit conflicting consensus operations:

  • The Double_preattestation_evidence operation allows for accusing a delegate of having double-preattested – i.e., of having preattested two different block candidates, at the same level and at the same round. The bulk of the evidence, the two arguments provided, consists of the two offending preattestations.

  • Similarly, the Double_attestation_evidence operation allows for accusing a delegate of having double-attested – i.e., of having attested two different block candidates at the same level and the same round – by providing the two offending attestations.

  • The Double_baking_evidence allows for accusing a delegate of having “double-baked” a block – i.e., of having signed two different blocks at the same level and at same round. The bulk of the evidence consists of the block headers of each of the two offending blocks.

See here for further detail on the semantics of evidence-providing operations.

The Activation operation allows users which participated in the Tezos fundraiser to make their accounts operational.

Finally, the Drain_delegate operation allows an active consensus-key account, i.e., an account to which a baker delegated its consensus-signing responsibility, to empty its delegate account. This operation is used as a deterrent to ensure that a delegate secures its consensus key as much as its manager (or main) key.

Manager Operations#

Manager operations enable end-users to interact with the Tezos blockchain – e.g., transferring funds or calling smart contracts. A manager operation is issued by a single manager account which signs the operation and pays the fees to the baker for its inclusion in a block. Indeed, manager operations are the only fee-paying and gas-consuming operations.

  • The Reveal operation reveals the public key of the sending manager. Knowing this public key is indeed necessary to check the signature of future operations signed by this manager.

  • The Transaction operation allows users to either transfer tez between accounts and/or to invoke a smart contract.

  • The Delegation operation allows users to delegate their stake to a delegate (a baker), or to register themselves as delegates.

  • The Update_consensus_key operation allows users to delegate the responsibility of signing blocks and consensus-related operations to another account. Note that consensus keys cannot be BLS public keys.

  • The Origination operation is used to originate, that is to deploy, smart contracts in the Tezos blockchain.

  • The Set_deposits_limit operation enables delegates to adjust the amount of stake a delegate has locked in bonds.

  • Support for registering global constants is implemented with the Register_global_constant operation.

  • The Increase_paid_storage operation allows a sender to increase the paid storage of some previously deployed contract.

  • The Event operation enables sending event-like information to external applications from Tezos smart contracts – see Contract Events for further detail.

Moreover, all operations necessary to implement Tezos’ enshrined Layer 2 solutions into the economic protocol are also manager operations.

In particular, smart rollups maintenance is handled with dedicated manager operations.

  • The Smart_rollup_originate operation is used to originate, that is, to deploy smart rollups in the Tezos blockchain.

  • The Smart_rollup_add_messages operation is used to add messages to the inbox shared by all the smart rollups originated in the Tezos blockchain. These messages are interpreted by the smart rollups according to their specific semantics.

  • The Smart_rollup_publish operation is used to regularly declare what is the new state of a given smart rollup in a so-called “commitment”. To publish commitments, a user account has to own at least ꜩ 10,000, which are frozen as long as at least one of their commitments is disputable.

  • The Smart_rollup_cement operation is used to cement a commitment, if the following requirements are met: it has been published for long enough, and there is no concurrent commitment for the same state update. Once a commitment is cemented, it cannot be disputed anymore.

  • The Smart_rollup_recover_bond operation is used by a user account to unfreeze their ꜩ 10,000. This operation only succeeds if and only if all the commitments published by the user account have been cemented.

  • The Smart_rollup_refute operation is used to start or pursue a dispute. A dispute is resolved on the Tezos blockchain through a so-called refutation game, where two players seek to prove the correctness of their respective commitment. The game consists in a dissection phase, where the two players narrow down their disagreement to a single execution step, and a resolution, where the players provide a proof sustaining their claims. The looser of a dispute looses their frozen bond: half of it is burned, and the winner receives the other half in compensation.

  • The Smart_rollup_timeout operation is used to put an end to a dispute if one of the two players takes too much time to send their next move (with a Smart_rollup_refute operation). It is not necessary to be one of the players to send this operation.

  • The Smart_rollup_execute_outbox_message operation is used to enact a transaction from a smart rollup to a smart contract, as authorized by a cemented commitment. The targeted smart contract can determine if it is called by a smart rollup using the SENDER Michelson instruction.

Manager Operation Batches#

Manager operations can be grouped, forming a so-called batch. Batches enable the inclusion of several manager operations from the same manager in a single block.

Batches satisfy the following properties:

  • All operations in a batch are issued by the same manager, which provides a single signature for the entire batch.

  • A batch is applied atomically: all its operations are executed sequentially, without interleaving other operations. Either all the operations in the batch succeed, or none is applied.

Failing_noop operation#

The Failing_noop operation is not executable in the protocol:

Rather, the Failing_noop operation allows to sign an arbitrary string, without introducing an operation that could be misinterpreted in the protocol.

The Octez client provides commands to sign and verify the signature of input messages by a given key. These commands create a failing_noop operation from the message that is being signed or checked.

octez-client sign message "hello world" for <account>

octez-client check that message "hello world" was signed by <account> to
produce <signature>