# Introduction to Cumulus

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Official documentation of Cumulus
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{% embed url="<https://paritytech.github.io/polkadot-sdk/master/polkadot_sdk_docs/polkadot_sdk/cumulus/index.html>" %}

<figure><img src="/files/Dqgb6ILkXI6euicFOXf5" alt=""><figcaption></figcaption></figure>

### What is Cumulus?

A set of tools for writing [Substrate](https://substrate.io/)-based [Polkadot](https://wiki.polkadot.network/en/) [parachains](https://wiki.polkadot.network/docs/en/learn-parachains). Refer to the included [overview](https://github.com/paritytech/polkadot-sdk/blob/master/cumulus/docs/overview.md) for architectural details, and the [Connect to a relay chain how-to guide](https://docs.substrate.io/reference/how-to-guides/parachains/connect-to-a-relay-chain/) for a guided walk-through of using these tools.

It's easy to write blockchains using Substrate, and the overhead of writing parachains' distribution, p2p, database, and synchronization layers should be just as low. This project aims to make it easy to write parachains for Polkadot by leveraging the power of Substrate.

Cumulus clouds are shaped sort of like dots; together they form a system that is intricate, beautiful and functional.

#### Consensus

[`parachain-consensus`](https://github.com/paritytech/polkadot-sdk/blob/master/cumulus/client/consensus/common/src/parachain_consensus.rs) is a [consensus engine](https://docs.substrate.io/v3/advanced/consensus) for Substrate that follows a Polkadot [relay chain](https://wiki.polkadot.network/docs/en/learn-architecture#relay-chain). This will run a Polkadot node internally, and dictate to the client and synchronization algorithms which chain to follow, [finalize](https://wiki.polkadot.network/docs/en/learn-consensus#probabilistic-vs-provable-finality), and treat as best.

#### Collator

A Polkadot [collator](https://wiki.polkadot.network/docs/en/learn-collator) for the parachain is implemented by the `polkadot-parachain` binary (previously called `polkadot-collator`).

You may run `polkadot-parachain` locally after building it or using one of the container option described [here](https://github.com/paritytech/polkadot-sdk/blob/master/cumulus/docs/contributor/container.md).

### Resources

{% embed url="<https://docs.substrate.io/tutorials/build-a-parachain/connect-a-local-parachain/>" %}


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