A modular blockchain is part of an architecture that distributes blockchain responsibilities across specialized layers. Instead of requiring one integrated system to perform every task, a modular design separates functions that can have different scaling needs and security assumptions. A layer may still perform more than one function.
The main responsibilities
Execution applies transactions to update balances and application state. Consensus establishes agreement on an ordered history. Data availability ensures that required data has been published and can be obtained. Settlement can verify state claims, resolve disputes and support transfers between layers, depending on the architecture.
For example, an execution layer can publish transaction data to Celestia, which provides consensus and data availability. Celestia making those bytes available does not, by itself, verify that the application's transactions follow its rules. That remains the responsibility of the execution and verification design.
Flexibility comes with dependencies
Separating functions lets developers choose execution environments and share infrastructure without building every component independently. It can also distribute resource demands and support scaling.
However, connections between layers need defined verification rules. Bridge contracts, data providers, upgrade authorities and differences in finality can introduce failures or trust assumptions. Modules cannot necessarily be swapped without migration or coordination. “Modular” describes an architecture, not a guarantee of interoperability, decentralization or superior security.