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🥷 For Searchers

Searcher Simluation

Bundles must only pass basic CheckTx validation (e.g. nonce, account balance, etc.) in order to be accepted by the auction. This means that bundles that are submitted to the auction may not be entirely valid on-chain since runMsgs is not executed. Searchers are encouraged to simulate their bundles before submitting them to the auction.

➡️ How do searchers submit bundles to chains that use the Block SDK?


💡 AuctionTx (auction bid transaction) = sdk.Tx that includes a single MsgAuctionBid

Searchers submit bundles by broadcasting a AuctionTx in the same way they broadcast any other transaction. A few important things to note:

  • When a MsgAuctionBid message is included in a transaction, no other sdk.Msg can be present.
  • Interfacing with the auction may be different across Block SDK chains. Bidding may involve interacting with a dedicated AuctionHouse smart contract instead of including this special message type. In the future, we will link a chain directory here to check on which interface you need, when there are different implementations.

Default Auction Bid Message

// MsgAuctionBid defines a request type for sending bids to the x/auction
// module.
type MsgAuctionBid struct {
// bidder is the address of the account that is submitting a bid to the
// auction.
Bidder string `protobuf:"bytes,1,opt,name=bidder,proto3" json:"bidder,omitempty"`
// bid is the amount of coins that the bidder is bidding to participate in the
// auction.
Bid types.Coin `protobuf:"bytes,3,opt,name=bid,proto3" json:"bid"`
// transactions are the bytes of the transactions that the bidder wants to
// bundle together.
Transactions [][]byte `protobuf:"bytes,4,rep,name=transactions,proto3" json:"transactions,omitempty"`

There are three things searchers must specify to participate in an auction:

  1. The Transactions they want executed at the top of block.
    • Transactions will be executed in the order they are specified in the message.
    • Each transactions included must be the raw bytes of the transaction.
  2. The Bidder who is bidding for top of block execution.
    • This must be the same account that signs the transaction.
  3. The Bid they want to send alongside the bundle.
    • This should be in the denom configured by the auction parameters (see below)
  4. The Timeout height i.e. until what height the bid is valid for.
    • This must be added to the transaction when it is being constructed i.e. txBuilder.SetTimeoutHeight(timeoutHeight)

Nonce Checking

In general, all bundles must respect nonce ordering of accounts. If a bundle is submitted with an invalid nonce, it will be rejected. The execution of the bundle will always look like the following:

  • Auction Transaction (which extracts the bid)
  • All transactions in the bundle (in order)

For example, assume the following:

  1. Searcher has account A with nonce n
  2. Searcher wants to submit a bundle with 3 transactions from account A

The searcher must first sign the AuctionTx with nonce n + 1. Then, the searcher must sign the first transaction in the bundle with nonce n + 2, the second transaction with nonce n + 3, and the third transaction with nonce n + 4.

Skipper Bot

User’s can bootstrap their searching bots by utilizing Skip’s own open source Skipper Bot.

Creating an AuctionTx

// createBidTx creates an auction bid tx with the given parameters
func createBidTx(
privateKey *secp256k1.PrivKey,
bidder string,
bid sdk.Coin,
bundle [][]byte,
height uint64,
sequenceOffset uint64,
) (sdk.Tx, error) {
// bid transaction can only include a single MsgAuctionBid
msgs := []sdk.Msg{
Bidder: bidder,
Bid: bid,
Transactions: bundle,

// Retrieve the expected account and sequence number
sequenceNum, accountNum := getAccountInfo(privateKey)

txConfig := authtx.NewTxConfig(
txBuilder := txConfig.NewTxBuilder()

// Set the messages along with other fee information

// ******************************************************
// ******************************************************

// Sign the auction transaction with nonce n + 1
// where n is the number of transactions in the bundle
// that are signed by the searcher
offsetNonce := sequenceNum + sequenceOffset
signerData := auth.SignerData{
AccountNumber: accountNumber,
Sequence: offsetNonce,

sigV2, err = clientTx.SignWithPrivKey(
if err != nil {
return nil, err

if err = txBuilder.SetSignatures(sigV2); err != nil {
return nil, error

return txBuilder.GetTx(), nil

⚙️ Auction fees

Auction Configuration

All auction parameters are accessible though the /block-sdk/x/auction/v1/params HTTP path on a standard node or gRPC service defined by x/auction.

In order to participate in an auction, searchers must pay a fee. This fee is paid in the native token of the chain. The fee is determined by the auction parameters, which are set by the chain. The auction parameters are:

  1. MaxBundleSize: specifies the maximum number of transactions that can be included in a bundle (bundle = an ordered list of transactions). Bundles must be ≤ this number.
  2. ReserveFee: specifies the bid floor to participate in the auction. Bids that are lower than the reserve fee are ignored.
  3. MinBidIncrement: specifies how much greater each subsequent bid must be (as seen by an individual node) in order to be considered. If the bid is lower than the highest current bid + min bid increment, the bid is ignored.
  4. FrontRunningProtection: determines whether front-running and sandwich protection is enabled.
Front-running and sandwich protection

If this is set to true, your bundle must follow these guidelines:

  • You must put your signed transactions after transactions you didn’t sign
  • You can only have at most two unique signers in the bundle

Bundle Examples:

  1. Valid: [tx1, tx2, tx3] where tx1 is signed by the signer 1 and tx2 and tx3 are signed by the bidder.
  2. Valid: [tx1, tx2, tx3, tx4] where tx1 - tx4 are signed by the bidder.
  3. Invalid: [tx1, tx2, tx3] where tx1 and tx3 are signed by the bidder and tx2 is signed by some other signer. (possible sandwich attack)
  4. Invalid: [tx1, tx2, tx3] where tx1 is signed by the bidder, and tx2, tx3 are signed by some other signer. (possible front-running attack)

Querying auction parameters

func getAuctionParams() (*auctiontypes.Params, error) {
# Replace this URL with the gRPC url of a node
url := "localhost:9090"

# Establish a gRPC connection to query auction parameters
grpcConn, err := grpc.Dial(
if err != nil {
return nil, err

client := auctiontypes.NewQueryClient(grpcConn)

req := &auctiontypes.QueryParamsRequest{}
resp, err := client.Params(context.Background(), req)

return resp.Params

🚨 Chains currently using the MEV-Lane


Chain NameChain-IDBlock-SDK Version


Chain NameChain-IDBlock-SDK Version