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⚡️ Integrate the Block SDK

Block SDK

The Block SDK is open-source software licensed under MIT. It is free to use, and has existing plug-and-play Lanes that work immediately!

Visit the GitHub repo here.

Please reach out to us if you need help!

⚙️ Architecture [15 mins]


This is a high-level overview of the architecture, please reference this page or the Block-SDK repo for detailed and up to date info. For those eager to code, feel free to skip this and start down the page at Set Up!

How Were Blocks Constructed pre-Block-SDK?

There are 3 relevant stages of consensus (these are all ABCI++ methods)

  • PrepareProposal
    • In this step, the consensus-engine (CometBFT, etc.) gives the application all of the transactions it has seen thus far.
    • The app looks over these, performs some app-specific logic, and then gives them back to the consensus-engine. The consensus-engine then creates and broadcasts a proposal containing the transactions sent back from the app.
  • ProcessProposal
    • In this step, all validators check that the transactions in the proposal are valid, and that the proposal (as a whole) satisfies validity conditions determined by the application
      • If the proposal fails, validators will not vote on the block, and the network will be forced to another round of consensus
      • if the proposal passes, valdiators vote on the block, and the block will become canonical (barring unforeseen events)

Application Mempools

In v0.47.0 of the cosmos-sdk, app-side mempools were added to the SDK. With app-side mempools, validators no longer need to rely on the consensus-engine to keep track of and order all available transactions. Now applications can define their own mempool implementations, that

  1. Store all pending (not finalized in a block) transactions
  2. Order the set of pending transactions

How does block-building change?

Now in PrepareProposal instead of getting transactions from the consensus-engine, validators can pull transactions from their application-state aware mempools, and prioritize those transactions instead of the consensus-engine's transactions.

Why is this better?

  • Mempools that are not app-state aware will not have the ability to make state-aware ordering rules. Like
  1. All staker transactions are placed at the top of the block
  2. All IBC LightClientUpdate messages are placed at the top of the block
  3. Anything you can think of!!
  • The consensus engine's mempool is generally in-efficient.
    • The consensus-engine's mempool does not know when to remove transactions from its own mempool
    • The consensus-engine spends most of its time re-broadcasting transactions between peers, hogging network bandwidth


The Block-SDK defines its own custom implementation of an app-side mempool, a LaneMempool. The LaneMempool is composed of Lanes, and handles transaction ingress, ordering, and cleaning.

transaction ingress

  • The LanedMempool constructor defines an ordering of lanes. When a transaction is received by the app, it iterates through all lanes in order and inserts the transaction into the first Lane that it belongs in. ordering
  • Each Lane of the LanedMempool maintains its own ordering of transactions. When the LanedMempool routes a transaction to its corresponding Lane the Lane then inserts the transaction at its designated position with respect to all other transactions in the lane


When the application is instructed to PrepareProposal it iterates through its Lanes in order, and calls each Lane's PrepareLane method. The Lane.PrepareLane method collects transactions from a Lane and appends those transactions to the set of transactions from previous Lane's PrepareLane calls. In other words, each block-proposal is now a collection of the transactions from the LanedMempool's constituent lanes.


When the application receives a proposal, and calls ProcessProposal, the app delegates the validation to the LaneMempool.ProcessLanes method. Remember, the proposal is composed of transactions from the sub-lanes of the LaneMempool, as such, the LaneMempool can route each Lane's contribution to the Proposal to that Lane for validation. The proposal passes iff all Lane's contributions are valid.


A block constructed from a LaneMempool's PrepareLanes method must always pass that LaneMempool's ProcessLanes method, otherwise, the chain will fail to produce blocks!! These functions are consensus critical, so practice caution when implementing them!!

📖 Set Up [20 mins]

To get set up, we're going to implement the Default Lane, which is the most general and least restrictive that accepts all transactions. This will cause no changes to your chain functionality, but will prepare you to add lanes with more functionality afterwards!

The default lane mirrors how CometBFT creates proposals today.

  • It does a basic check to ensure that the transaction is valid.
  • Orders the transactions based on tx fee amount (highest to lowest).
  • The PrepareLane handler will reap transactions from the lane up to the MaxBlockSpace limit
  • The ProcessLane handler will ensure that the transactions are ordered based on their fee amount and pass the same checks done in PrepareLane.

🏗️ Default Lane Setup

📦 Dependencies

The Block SDK is built on top of the Cosmos SDK. The Block SDK is currently compatible with Cosmos SDK versions greater than or equal to v0.47.0.

Release Compatibility Matrix

Block SDK VersionCosmos SDK

📥 Installation

To install the Block SDK, run the following command:

$ go install

📚 Usage

  1. First determine the set of lanes that you want to use in your application. The available lanes can be found in our Lane App Store. This guide only sets up the default lane
import (
defaultlane ""

// 1. Create the lanes.
// NOTE: The lanes are ordered by priority. The first lane is the highest priority
// lane and the last lane is the lowest priority lane. Top of block lane allows
// transactions to bid for inclusion at the top of the next block.
// For more information on how to utilize the LaneConfig please
// visit the README in
// Default lane accepts all transactions.

func NewApp() {
defaultConfig := base.LaneConfig{
Logger: app.Logger(),
TxEncoder: app.txConfig.TxEncoder(),
TxDecoder: app.txConfig.TxDecoder(),
MaxBlockSpace: math.LegacyZeroDec(),
MaxTxs: 0,
defaultLane := defaultlane.NewDefaultLane(defaultConfig)
// TODO(you): Add more Lanes!!!
  1. In your base application, you will need to create a LanedMempool composed of the lanes you want to use.
        // 2. Set up the relative priority of lanes
lanes := []block.Lane{
mempool := block.NewLanedMempool(app.Logger(), true, lanes...)
  1. Next, order the lanes by priority. The first lane is the highest priority lane and the last lane is the lowest priority lane. It is recommended that the last lane is the default lane.
    // 3. Set up the ante handler.
anteDecorators := []sdk.AnteDecorator{

anteHandler := sdk.ChainAnteDecorators(anteDecorators...)

// Set the lane ante handlers on the lanes.
// NOTE: This step is very important. Without the antehandlers, lanes will not
// be able to verify transactions.
for _, lane := range lanes {
  1. You will also need to create a PrepareProposalHandler and a ProcessProposalHandler that will be responsible for preparing and processing proposals respectively. Configure the order of the lanes in the PrepareProposalHandler and ProcessProposalHandler to match the order of the lanes in the LanedMempool.
    // 4. Set the abci handlers on base app
// Create the LanedMempool's ProposalHandler
proposalHandler := abci.NewProposalHandler(

// set the Prepare / ProcessProposal Handlers on the app to be the `LanedMempool`'s

💅 Next step: implement other lanes

Visit our Lane App Store and select the lanes you want, or Build Your Own.