The off-chain system is a peer-to-peer network of Hubs that store user data. Most user actions are processed and stored within these Hubs, including:

• Posting new content.

• Following other users.

• Reacting to posts.

• Updating profile pictures.

Farcaster’s on-chain system is deployed on the Optimism mainnet to ensure security and data consistency. On-chain actions are kept minimal to reduce costs and optimize performance, and include:

• Creating new accounts.

• Paying for data storage.

• Adding account keys for connected apps.

Hubs function as distributed, peer-to-peer servers for validating and storing off-chain data. Users can set up their own Hub by installing it on a VPS. Each Hub synchronizes both on-chain data from Ethereum and off-chain data from other Hubs, storing a full copy of Farcaster’s data accessible via APIs.

When a validator node is involved, it ensures the integrity of every action within the Hub network. For example, when a user posts a message, it is signed with their account key. The message is then sent to a Hub, where validators verify it through signature checks and property validation. After validation, the message is stored locally, replicated across other Hubs, and synchronized with both the Layer-2 Optimism and Layer-1 Ethereum databases.

This structure ensures secure, efficient data management while maintaining decentralized storage and network-wide synchronization.