Skip to main content

Polkadot Relay Chain

Before you get started on your journey towards becoming an Astar network hacker, it will be beneficial to know about what Polkadot is, and its relationship to Astar. If you are already building on Astar you will not need to go over the sections covering Substrate and how to create a Runtime, but it will be helpful for you to understand the environment, terminology and how to leverage this interconnected network of blockchains, that's right within your grasp.

Polkadot is a multi-chain environment which enables specialized blockchains (called Parachains) to communicate with each other in a secure, trustless environment.

Astar is a blockchain connected to Polkadot Relay chain, specialized for:

  • Executing all types of smart contracts.
  • Providing a hybrid EVM + Wasm environment supporting Cross-VM (XVM) smart contract calls.
  • Incentivizing ecosystem innovation and providing basic income for dApp developers.
  • Seamlessly aggregating features or assets from parachains in the ecosystem.

Blockchain Basics

A blockchain is a decentralized ledger that records information in a sequence of blocks. The information contained in a block is an ordered set of instructions that may or may not result in a change in state.

In a blockchain network, individual computers—called nodes—communicate with each other to form a decentralized peer-to-peer (P2P) network. There is no central authority that controls the network and, typically, each node that participates in block production stores a copy of the blocks that make up the canonical chain.

In most cases, users interact with a blockchain by submitting a request that might result in a change in state, for example, a request to change the owner of a file or to transfer funds from one account to another. These transactions requests are gossiped to other nodes on the network and assembled into a block by a block author. To ensure the security of the data on the chain and the ongoing progress of the chain, the nodes use some form of consensus to agree on the state of the data in each block and on the order of transactions executed. Read more...

What is Polkadot

To get started, let's kick it off with two short videos that do a very good job at explaining some core concepts around Polkadot. First, watch Bill Laboon, Director of Education and Support at the Web3 Foundation, explain the basics of Polkadot.

Ok, you can’t learn it all in one minute. But how about in 5 minutes? Have a look at this excellent video from DeFi Teller, explaining how Polkadot works.

How the Relay Chain Works

The Polkadot network uses a sharded model where shards - called "parachains", allow transactions to be processed in parallel instead of sequentially. Each parachain in the network has a unique state transition function. Polkadot is a Relay Chain acting as the main chain of the system.

Parachains construct and propose blocks to validators on the Relay Chain, where the blocks undergo rigorous availability and validity checks before being added to the finalized chain. As the Relay Chain provides the security guarantees, collators - full nodes of these parachains - don't have any security responsibilities, and thus do not require a robust incentive system. This is how the entire network stays up to date with the many transactions that take place.


Based on Polkadot's design, as long as a chain's logic can compile to Wasm and adheres to the Relay Chain API, then it can connect to the Polkadot network as a parachain. However, the majority of parachains today are built using Substrate because Substrate-based chains are easy to integrate into Polkadot or Kusama to become a parachain. Essentially, Substrate is the SDK which can be used to build parachains and Polkadot is the means of securing the chains and allowing them to communicate with each other.

At a high level, a Substrate node provides a layered environment with two main elements:

  1. An outer node that handles network activity such as peer discovery, managing transaction requests, reaching consensus with peers, and responding to RPC calls.
  2. A runtime that contains all of the business logic for executing the state transition function of the blockchain. Read more about Architecture.


FRAME is an acronym for Framework for Runtime Aggregation of Modularized Entities which encompasses a significant number of modules and support libraries that simplify runtime development. In Substrate, these modules (called pallets) offer customizable business logic for different use cases and features that you might want to include in your runtime. For example, there are pallets that provide a framework of business logic for staking, consensus, governance, and other common activities. Read more about Runtime development

Applications Running on a Blockchain

Applications that run on a blockchain, often referred to as decentralized applications or dApps, are typically web applications written using front-end frameworks, but powered by smart contracts on the backend, to affect the blockchain state.

A smart contract is a program that runs on a blockchain and executes transactions on behalf of users under specific conditions. Developers can write smart contracts to ensure that the outcomes of programmatically-executed transactions are recorded, and can't be tampered with. Yet, smart contracts operate in a sandboxed environment, where developers don't have access to underlying blockchain functionality, such as consensus, storage, or transaction layers, and instead, abide by a chain's fixed rules and restrictions. Smart contract developers often accept these limitations as a tradeoff that shortens the development lifecycle, by avoiding having to make core design decisions.

Where Do Smart Contracts Execute?

The Polkadot runtime does not support smart contracts. Smart contracts require a Virtual Machine (VM) environment where contracts can be executed, and the most well-known and widely supported platform being the Ethereum Virtual Machine (EVM). Substrate FRAME contains modules that support Wasm smart contract execution, as well as EVM.

Ethereum Virtual Machine (EVM)

The Ethereum Virtual Machine (EVM) is a virtual computer with components that enable Ethereum network participants to store data and agree on the state of that data. On a Substrate-based blockchain, the core responsibilities of the EVM are implemented in the EVM pallet, that's responsible for executing Ethereum contract bytecode written in a high level language like Solidity. Astar EVM provides a fully Ethereum Virtual Machine compatible platform, which you can learn more about in the EVM chapter.

Substrate Virtual Machine for Wasm Contracts

Substrate also ships with a module for smart contracts, called pallet-contracts. If a parachain is developed on Substrate it can easily add smart contract functionality by including this pallet. Astar supports this Polkadot Native approach to smart contracts, and you can learn more in the Wasm chapter.