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How to view and deploy parachains

The guide has been updated to work with the Alexander testnet.

How to view parachains

On the Polkadot UI navigate to the Chain State tab. Select the parachains module and the parachains() then hit the + button. It will return an array of the currently active parachains.

How to deploy the Adder parachain

You will need to have the minimum deposit needed to create a referendum. Currently this minimum is 5 DOTs.

The adder parachain is a simple parachain which will keep a value in storage and add to this value as messages are sent to it. It can be found in the Polkadot repository under the test-parachains folder.

A slightly out-of-date video version of this guide presented by Adrian Brink is available here. When the two guides diverge, please refer to this written text as definitive and updated.

Building the code

The first step is to download locally the Polkadot code and switch to the v0.4 branch.

git clone
cd polkadot
git checkout v0.4

Now make sure you have Rust installed.

curl -sSf | sh
sudo apt install make clang pkg-config libssl-dev
rustup update

Now navigate to the test-parachains folder in the Polkadot code repository and run the build script.

cd test-parachains

This will create the Wasm executable of the simple adder parachain contained in this folder. This parachain will simply add messages that are sent to it. The Wasm executable will output into the parachains/test/res/adder.wasm path so make sure you are able to find it there.

You will need to build and run the collator node in order to get the genesis state of this parachain.

Navigate to the test-parachains/adder/collator directory and run the build and run commands.

cargo build
cargo run

Feel free to stop the collator node right away. You will get some output that looks like this:

Starting adder collator with genesis:
Dec: [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 27, 77, 3, 221, 140, 1, 241, 4, 145, 67,
207, 156, 76, 129, 126, 75, 22, 127, 29, 27, 131, 229, 198, 240, 241, 13, 137, 186, 30, 123, 206]
Hex: 0x00000000000000000000000000000000000000000000000000000000000000000000000000000000011b4d03dd8c01f1049143cf9c4c817e4b167f1d1b83e5c6f0f10d89ba1e7bce

The important information is the hex string. This is your genesis state and you will need to save it for the next steps.

Deploying the parachain

Go to Polkadot UI on the Extrinsics tab. Select the account you wish to deploy the parachain from. You will need to create a referendum to deploy the parachain.

Click on democracy -> propose(proposal,value) -> parachains -> registerParachain(id,code,initial_head_data).

In the id input enter in the id of the parachain. In the case of the simple adder it will be 100. In the code field click on the page button and then upload the adder.wasm binary that was compiled from before. In the initial_head_data we will copy and paste the hex data that we got from running the collator node. In the value field you will need to input the minimum required value for creating a referendum. At the time of writing this is 5 DOTs on the Alexander testnet.

registering a parachain

If you navigate to the Democracy tab you will be able to see your proposal in the proposals section.

Once you wait for the proposal to become a referendum you will be able to vote Nay or Aye on it. Assumably, you will vote Aye as this will be a vote for the deployment of your parachain.

parachain referendum

After the voting period of your referendum goes through you will be able to query the state of your parachain.

You can go to the Chain State tab and by querying the parachains state you should be able to see some information on your parachain.

parachain info

Interacting with the parachain

Coming soon