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Documentation Index

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The Nexus module is the backbone of Axelar’s interoperability protocol. It maintains a registry of all supported chains, routes cross-chain messages and asset transfers between them, tracks transfer states, and manages the set of validator maintainers responsible for each external chain. Every asset transfer and general message that moves through Axelar passes through this module.

Chain Registry

Maintains the canonical list of active and inactive chains, including EVM, IBC Cosmos, and CosmWasm chains.

Message Routing

Routes GeneralMessage objects from source chains to destination chains via registered MessageRoute handlers.

Asset Management

Registers assets on chains, tracks cross-chain transfer states, and manages fee configuration per chain/asset pair.

Chain Maintainers

Tracks which bonded validators maintain each external chain, enforcing participation thresholds to ensure liveness.

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Key Concepts

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Chain

A Chain represents any blockchain network registered with Axelar. Each chain has a unique name, an associated module (e.g., evm, axelarnet), and a key type. 
// Validate performs a stateless check to ensure the Chain object has been initialized correctly
func (m Chain) Validate() error {
    if err := m.Name.Validate(); err != nil {
        return errorsmod.Wrap(err, "invalid chain name")
    }
    if err := m.KeyType.Validate(); err != nil {
        return err
    }
    if m.Module == "" {
        return fmt.Errorf("missing module name")
    }
    return nil
}

​
CrossChainAddress

A CrossChainAddress pairs a chain with a native address string on that chain: 
func (m CrossChainAddress) Validate() error {
    if err := m.Chain.Validate(); err != nil {
        return err
    }
    if err := utils.ValidateString(m.Address); err != nil {
        return errorsmod.Wrap(err, "invalid address")
    }
    return nil
}

​
CrossChainTransfer

A CrossChainTransfer records a pending or completed asset transfer including a unique TransferID, a CrossChainAddress recipient, a sdk.Coin asset, and a TransferState. 
func NewPendingCrossChainTransfer(id uint64, recipient CrossChainAddress, asset sdk.Coin) CrossChainTransfer {
    return NewCrossChainTransfer(id, recipient, asset, Pending)
}

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TransferState

Transfers move through the following states:
StateDescription
TRANSFER_STATE_PENDINGQueued but not yet executed
TRANSFER_STATE_ARCHIVEDSuccessfully completed
TRANSFER_STATE_INSUFFICIENT_AMOUNTRejected because the transferred amount did not cover the minimum fee
TRANSFER_STATE_FAILEDTransfer failed during execution

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GeneralMessage

A GeneralMessage is an arbitrary cross-chain payload — for example, a GMP call from an EVM chain. The Nexus module routes it to the correct destination module via a registered MessageRoute. 
type MessageRoute func(ctx sdk.Context, routingCtx RoutingContext, msg GeneralMessage) error

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FeeInfo

Fees are registered per chain-asset pair with a rate, minimum, and maximum: 
func NewFeeInfo(chain ChainName, asset string, feeRate math.LegacyDec, minFee math.Int, maxFee math.Int) FeeInfo {
    return FeeInfo{Chain: chain, Asset: asset, FeeRate: feeRate, MinFee: minFee, MaxFee: maxFee}
}

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Message Routing Flow

When a cross-chain message is created on a source chain, Nexus processes it as follows:
  1. The source chain module (EVM or axelarnet) submits the GeneralMessage to Nexus.
  2. Nexus looks up the destination chain and retrieves the registered MessageRoute.
  3. If the route exists, the message is dispatched to the destination module’s handler.
  4. On success the message is marked APPROVED; on failure it transitions to FAILED and can be retried.
Failed general messages can be retried using axelard tx nexus retry-failed-message [id]. This re-invokes the routing logic without requiring a new source-chain event.

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Chain Registration & Maintainers

Chains are registered at genesis or via governance. Once registered, bonded validators can opt in as chain maintainers — they are responsible for monitoring and voting on that chain’s events. 
# Register your proxy as a chain maintainer for Ethereum and Avalanche
axelard tx nexus register-chain-maintainer ethereum avalanche \
  --from <proxy-key> \
  --chain-id axelar-dojo-1

# Remove yourself as a maintainer
axelard tx nexus deregister-chain-maintainer ethereum \
  --from <proxy-key> \
  --chain-id axelar-dojo-1
A validator must have registered a proxy account (via the snapshot module) before calling register-chain-maintainer. Calls from an unregistered proxy return an error.

​
Activate / Deactivate Chains

Governance or authorized accounts can activate and deactivate chains: 
axelard tx nexus activate-chain ethereum \
  --from <gov-key> \
  --chain-id axelar-dojo-1

axelard tx nexus deactivate-chain ethereum \
  --from <gov-key> \
  --chain-id axelar-dojo-1

​
Asset Fee Registration

Register or update the fee schedule for an asset on a specific chain: 
axelard tx nexus register-asset-fee \
  --chain ethereum \
  --asset uusdc \
  --fee-rate 0.001 \
  --min-fee 1000 \
  --max-fee 1000000 \
  --from <gov-key> \
  --chain-id axelar-dojo-1

​
Module Parameters

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ChainActivationThreshold
Threshold
required
Fraction of voting power required to activate a chain. Default: 55/100.
​
ChainMaintainerMissingVoteThreshold
Threshold
required
Fraction of missed votes within the check window before a maintainer is penalized. Default: 20/100.
​
ChainMaintainerIncorrectVoteThreshold
Threshold
required
Fraction of incorrect votes within the check window before a maintainer is penalized. Default: 15/100.
​
ChainMaintainerCheckWindow
int32
required
Number of recent blocks used to evaluate maintainer vote quality. Default: 500.
​
Gateway
sdk.AccAddress
Bech32 address of the Axelar Gateway account used for on-chain fee collection. Empty by default.
​
EndBlockerLimit
uint64
required
Maximum number of pending transfers processed per block in the end blocker. Default: 50.

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CLI Reference

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Query Commands

# List all registered chains
axelard query nexus chains

# Get chain state (active/inactive, assets)
axelard query nexus chain-state ethereum

# Query a general message by ID
axelard query nexus message [id]

# List assets registered on a chain
axelard query nexus assets ethereum

# Query fee info for a chain/asset pair
axelard query nexus fee-info ethereum uusdc

# Estimate the fee for a cross-chain transfer
axelard query nexus transfer-fee \
  --source-chain ethereum \
  --dest-chain osmosis \
  --asset uusdc \
  --amount 1000000

# List chain maintainers for a chain
axelard query nexus chain-maintainers ethereum

# Query pending/completed transfers for a chain
axelard query nexus transfers-for-chain ethereum --state pending

# Show nexus module parameters
axelard query nexus params

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Transaction Commands

# Register as chain maintainer
axelard tx nexus register-chain-maintainer ethereum avalanche \
  --from <proxy-key>

# Deregister as chain maintainer
axelard tx nexus deregister-chain-maintainer ethereum \
  --from <proxy-key>

# Activate a chain
axelard tx nexus activate-chain ethereum \
  --from <gov-key>

# Deactivate a chain
axelard tx nexus deactivate-chain ethereum \
  --from <gov-key>

# Register asset fee
axelard tx nexus register-asset-fee \
  --chain ethereum --asset uusdc \
  --fee-rate 0.001 --min-fee 1000 --max-fee 1000000 \
  --from <gov-key>

# Retry a failed general message
axelard tx nexus retry-failed-message [id] \
  --from <any-key>
Use axelard query nexus chain-by-asset [denom] to discover all chains on which a given asset denom is registered. This is helpful when constructing cross-chain transfer paths.

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