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Arcium.toml is auto-generated by arcium init and configures the Arcium CLI tooling. It lives at the root of your project alongside Anchor.toml. Most projects only need to edit this file when changing localnet behavior or adding a cluster offset for devnet or mainnet testing.

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Localnet configuration

The [localnet] section controls your local development cluster. All required fields are auto-generated by arcium init with sensible defaults.
FieldTypeRequiredDefaultDescription
nodesintegerYes2Number of MPC nodes. Minimum: 2
nodes_ipsarray of [u8; 4]NoSequential from 172.20.0.100IPv4 addresses for each node
localnet_timeout_secsintegerYes60Seconds to wait for localnet startup
backendsarray of stringNo["Cerberus"]MPC backends (only "Cerberus" supported)
Use the default values unless you need to test against a larger local cluster or a custom Docker network setup.

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Cluster configuration

The [clusters.<name>] sections map network names to cluster offsets. These entries are used by arcium test --cluster <name> to resolve the cluster offset for testing.
FieldTypeRequiredDescription
offsetintegerYesCluster offset for PDA derivation. See Deployment - Cluster offsets for current values.
The CLI reads these entries when you run commands such as: 
arcium test --cluster devnet
For local tests without a --cluster argument, the CLI uses the [localnet] configuration.

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Full example

[localnet]
nodes = 2
nodes_ips = [
  [172, 20, 0, 100],
  [172, 20, 0, 101]
]
localnet_timeout_secs = 60
backends = ["Cerberus"]

[clusters.devnet]
offset = 456

[clusters.mainnet]
offset = 2026

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Common mistakes

IssueFix
arcium test --cluster <name> cannot find a clusterAdd [clusters.<name>] with an offset field
Tests derive the wrong cluster accountCheck that the offset matches the target network
Localnet startup times outIncrease localnet_timeout_secs or reduce local resource contention
Custom node IPs do not workKeep nodes and nodes_ips lengths aligned