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Chainlinking Cosmos: A step-by-step guide to building your own blockchain with code examples

The Cosmos blockchain is an exciting development that allows developers to create their own blockchain with customized features. This technology has the potential to revolutionize the way we think about decentralized applications and create new opportunities for entrepreneurs and developers.

In this article, we will explore how to build a chain using the Cosmos blockchain with code examples. We will cover the basics of the Cosmos SDK, discuss the steps involved in building a custom chain, and provide examples to demonstrate how the different components of a chain come together.

What is the Cosmos SDK?

The Cosmos SDK is a developer-friendly toolkit for building blockchain applications. It includes a range of modules and tools that allow developers to create customized chains with built-in features like staking, governance, and account management.

One of the key advantages of the Cosmos SDK is its modular design. This allows developers to pick and choose the features they need, rather than being forced to use a one-size-fits-all approach.

The Cosmos SDK also includes support for the Tendermint consensus algorithm, which provides fast, secure and consistent block validation. This makes it an ideal tool for building scalable and reliable applications.

The Steps Involved in Building a Custom Chain

Building a Cosmos chain involves several steps, including:

  1. Installing the Cosmos SDK
  2. Creating a new chain directory
  3. Initializing the configuration for the new chain
  4. Defining the genesis file
  5. Configuring validators and nodes
  6. Running the new chain

Step 1: Installing the Cosmos SDK

Before you can start building your chain, you’ll need to install the Cosmos SDK. You can download the latest version from the official Cosmos repository on GitHub.

Once you’ve downloaded the files, you can install them by running the following command:

make install

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This will install the Cosmos SDK and all of its dependencies.

Step 2: Creating a New Chain Directory

Once you’ve installed the Cosmos SDK, you can create a new directory for your chain using the following command:

mkdir mychain
cd mychain

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Step 3: Initializing the Configuration for the New Chain

To initialize the configuration for your new chain, you can use the following command:

init <moniker> --chain-id <chain-id>

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Replace <moniker> with a label for your chain, and <chain-id> with a unique identifier for your chain.

Step 4: Defining the Genesis File

The genesis file defines the initial state of your blockchain, including the initial validator set and distribution of tokens.

To create the genesis file, you’ll need to define the initial validator set and the total number of tokens. You can do this using the following commands:

gentx --name <validator-name> --amount <staking-amount>

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Replace <validator-name> with your chosen label for a validator, and <staking-amount> with the amount of tokens you want to stake.

Step 5: Configuring Validators and Nodes

Once you’ve created the genesis file, you can configure validators and nodes by creating a config.toml file in the root directory of your chain. This file includes various configuration options, such as:

  • P2P networking
  • Consensus parameters
  • Fee structures
  • Node-specific settings

Here’s an example of what a config.toml file might look like:

# P2P networking settings
laddr = "tcp://"

# Consensus parameters
wal_file = "data/cs.wal/wal"
timeout_commit = "5s"
skip_timeout_commit = false
create_empty_blocks = true

# Fee structures
amount = 0
gas = 200000

# Node-specific settings
priv_validator_file = "data/priv_validator_key.json"

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Step 6: Running the New Chain

To start your new chain, you can use the following command:


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This will start the chain in a separate terminal window, allowing you to monitor its progress and make adjustments as needed.

Code Examples

Now that we’ve covered the basic steps involved in building a custom chain using the Cosmos SDK, let’s take a look at some code examples to see how the different components of a chain come together.

Defining a Module

Modules are the building blocks of a Cosmos chain. They define the functionality of your chain by specifying the types of messages it can process and the transactions it can execute.

Here’s an example of how to define a module in the Cosmos SDK:

type MyModule struct {}

func (m MyModule) Name() string {
  return "mymodule"

func (m MyModule) RegisterCodec(cdc *codec.Codec) {
  cdc.RegisterConcrete(&MyMsg{}, "mymodule/MyMsg", nil)

func (m MyModule) DefaultGenesis() json.RawMessage {
  return []byte{}

func (m MyModule) ValidateGenesis(data GenesisState) error {
  return nil

func (m MyModule) BeforeBlockCommit(ctx sdk.Context, txs []sdk.Tx) {
  // do something before the block is committed

func (m MyModule) AfterBlockCommit(ctx sdk.Context) {
  // do something after the block is committed

func (m MyModule) HandleMsg(ctx sdk.Context, msg Msg) sdk.Result {
  switch msg := msg.(type) {
  case *MyMsg:
    // process MyMsg
    return sdk.Result{}
    return sdk.ErrUnknownRequest("unknown message type")

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This example module defines a custom message type called MyMsg, along with implementations for various functions that are required by the Cosmos SDK.

Creating a Transaction

Transactions are the basic units of action in a Cosmos chain. They allow users to perform actions like transferring tokens, voting on proposals, and submitting new code.

Here’s an example of how to create a transaction in the Cosmos SDK:

tx := Tx{
  Msgs: []sdk.Msg{
      To: "cosmos1tfxswyxv2257drf3325yxm6trss5ls5d5l5lq3",
      From: "cosmos13yp0lf2w82fkl6rmv7p8gdh6dhm7y9a6cuflf",
      Amount: sdk.Coin{Denom: "stake", Amount: sdk.NewInt(100)},
  Fee: sdk.NewCoins(sdk.NewCoin("stake", sdk.NewInt(10))),
  Signatures: []sdk.StdSignature{
      PubKey: pk,
      Signature: sig,

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This example transaction transfers 100 stake tokens from one account to another, with a fee of 10 stake tokens. It includes a signature to verify its authenticity and to prevent fraud.

Validating Incoming Transactions

Once a transaction is received by the chain, it needs to be validated to ensure that it meets the requirements of the Cosmos SDK.

Here’s an example of how to validate incoming transactions in the Cosmos SDK:

func ValidateTransaction(tx Tx) error {
  if len(tx.Msgs) != 1 {
    return errors.New("transaction must have exactly one message")

  if tx.Fee.Amount.LT(sdk.NewInt(1)) {
    return errors.New("transaction fee must be at least 1 token")

  return nil

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This example function validates that the transaction includes exactly one message, and that the transaction fee is at least 1 token. If the transaction fails to meet these requirements, it will be rejected by the chain.


Building a custom chain using the Cosmos SDK may seem daunting at first, but with the right toolkit and guidance, it can be a rewarding and exciting experience. By following the steps outlined in this article, you can create your own custom blockchain with unique features and capabilities.

Whether you’re a seasoned developer or a new entrepreneur looking to break into the world of blockchain technology, the Cosmos SDK provides a powerful and versatile toolkit that can help you achieve your goals. So why not give it a try and see what kinds of innovative solutions you can create?

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