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Version: Endpoint V2 Docs

Omnichain Composability

Composability is a core requirement for building advanced, interconnected cross-chain applications.

LayerZero’s framework for composability breaks complex cross-chain interactions into discrete, sequential steps rather than forcing all operations into one atomic transaction. This design not only simplifies development, but also ensures that each step achieves instant and irreversible finality.

The Need for Cross-Chain Composability​

On a single blockchain, composability is straightforward – any smart contract can call others on the same network. However, when you have many different blockchains, things get siloed. A smart contract traditionally can only compose with contracts on its own chain, making it hard to build applications that span multiple networks​.

This lack of interoperability leads to fragmented liquidity and user experiences, as developers have to deploy all instances of an app on each chain to reach users there. Cross-chain composability aims to remove these barriers by letting contracts on different chains interact as easily as those on one chain. In other words, it unlocks an “omnichain” world where a single unified application can live across multiple blockchains.

Horizontal Composability in LayerZero​

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  • Mitigating atomicity limitations:
    In cross-chain scenarios, an all-or-nothing (atomic) transaction may seem ideal, but if one function call fails in a long chain of operations, the entire process is reverted. Horizontal composability mitigates this risk by treating each step as a separate message, reducing the potential for cascading failures.

  • Improving cross-chain user experience:
    By splitting operations into independent messages, users experience more predictable outcomes. For example, one message may transfer tokens in one operation, while a follow-up message triggers additional logic such as staking or swapping. Each step has its own execution context and error handling, ensuring that a failure in one part doesn’t necessarily cancel the entire operation of bridging.

  • Supporting advanced workflows:
    The framework enables sophisticated multi-chain applications. Whether coordinating token transfers with additional business logic or initiating sequential actions on different chains, horizontal composability provides the flexibility needed to build robust, complex cross-chain solutions.

  • Ensuring instant guaranteed finality:
    Finality is the assurance that once a transaction is confirmed, it cannot be reversed. LayerZero’s framework guarantees that every step in a cross-chain operation reaches finality as soon as it is processed. This instant, irrevocable finality is invaluable in cross-chain scenarios, as it prevents inconsistencies between chains and instills user trust, making cross-chain interactions as reliable as single-chain transactions.

How Composability Works​

  1. Initial message dispatch:
    The source application initiates a cross-chain call using LayerZero’s messaging protocol. This call triggers a primary state change, such as transferring tokens or updating a record.

  2. Triggering a composed message:
    After the primary operation is processed, the receiving application constructs and dispatches a follow-up, or composed, message. This secondary message is sent as an independent packet to the LayerZero Endpoint and includes context such as a unique identifier, source chain data, and additional parameters needed for the next action (either from the sender or application itself).

  3. Composer role:
    The same Executor service that delivered the initial message packet to the receiving application calls a dedicated composer contract for composed messages. When it receives a call, the composer processes the message and executes the next step in the workflow—whether that’s another state update, executing business logic, or interacting with an external protocol. In effect, the composer acts as a coordinator that links the independent steps together.

  4. Decoupled error handling:
    Since each step is executed as a separate transaction, a failure in one composed message does not automatically revert the original cross-chain operation. This decoupling allows issues to be isolated, retried, or compensated for without impacting the overall process.

Broad Impact Across Environments​

Regardless of the underlying blockchain, the core principles of horizontal composability remain consistent:

  • Message-based interaction:
    Every step in the process is communicated as an independent message.

  • Separation of concerns:
    Each operation has a clear, self-contained responsibility, enhancing modularity and simplifying debugging.

  • Flexible execution:
    Developers can set gas limits, fee configurations, and execution parameters independently for each message. This flexibility ensures that every cross-chain call is optimized for its specific environment.

Further Reading​

For VM-specific guides, developers can refer to:

By leveraging dedicated composer contracts and a structured messaging system, LayerZero’s horizontal composability framework allows developers to build resilient and complex cross-chain applications.