> ## Documentation Index
> Fetch the complete documentation index at: https://docs.arcium.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Arcium.toml

> Configuration reference for the Arcium CLI tooling suite

`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.

## Localnet configuration

The `[localnet]` section controls your local development cluster. All required fields are auto-generated by `arcium init` with sensible defaults.

| Field                   | Type               | Required | Default                        | Description                                |
| ----------------------- | ------------------ | -------- | ------------------------------ | ------------------------------------------ |
| `nodes`                 | integer            | Yes      | `2`                            | Number of MPC nodes. Minimum: 2            |
| `nodes_ips`             | array of `[u8; 4]` | No       | Sequential from `172.20.0.100` | IPv4 addresses for each node               |
| `localnet_timeout_secs` | integer            | Yes      | `60`                           | Seconds to wait for localnet startup       |
| `backends`              | array of string    | No       | `["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.

## 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.

| Field    | Type    | Required | Description                                                                                                                                     |
| -------- | ------- | -------- | ----------------------------------------------------------------------------------------------------------------------------------------------- |
| `offset` | integer | Yes      | Cluster offset for PDA derivation. See [Deployment - Cluster offsets](/developers/deployment#understanding-cluster-offsets) for current values. |

The CLI reads these entries when you run commands such as:

```bash theme={null}
arcium test --cluster devnet
```

For local tests without a `--cluster` argument, the CLI uses the `[localnet]` configuration.

## Full example

```toml theme={null}
[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
```

## Common mistakes

| Issue                                                | Fix                                                                  |
| ---------------------------------------------------- | -------------------------------------------------------------------- |
| `arcium test --cluster <name>` cannot find a cluster | Add `[clusters.<name>]` with an `offset` field                       |
| Tests derive the wrong cluster account               | Check that the offset matches the target network                     |
| Localnet startup times out                           | Increase `localnet_timeout_secs` or reduce local resource contention |
| Custom node IPs do not work                          | Keep `nodes` and `nodes_ips` lengths aligned                         |