fabro/docs/execution/run-configuration.mdx

---
title: "Run Configuration"
description: "Configure workflow runs with TOML files"
---

A run config is a TOML file that bundles a workflow graph with all the settings needed to execute it — the goal, model, sandbox, setup commands, variables, and hooks. Instead of passing a dozen CLI flags, you check a `.toml` file into version control and launch with a single command:

```bash
arc run start run.toml
```

## Minimal example

A run config requires three fields:

```toml title="run.toml"
version = 1
goal = "Implement the login feature"
graph = "workflow.dot"
```

| Field | Description |
|---|---|
| `version` | Config format version. Must be `1`. |
| `goal` | What the workflow should accomplish. Passed to agents and used in retrospectives. |
| `graph` | Path to the DOT workflow file, resolved relative to the TOML file's directory. |

## Full example

```toml title="run.toml"
version = 1
goal = "Run the CI pipeline for $repo_name"
graph = "pipelines/ci.dot"
directory = "/tmp/workdir"

[llm]
model = "claude-sonnet-4-5"
provider = "anthropic"

[llm.fallbacks]
anthropic = ["gemini", "openai"]
gemini = ["anthropic", "openai"]

[setup]
commands = ["git clone $repo_url repo", "cd repo && npm install"]
timeout_ms = 120000

[sandbox]
provider = "daytona"
preserve = false

[sandbox.daytona]
auto_stop_interval = 60

[sandbox.daytona.labels]
project = "arc"
env = "ci"

[sandbox.daytona.snapshot]
name = "node-20"
cpu = 4
memory = 8
disk = 20
dockerfile = "FROM node:20-slim\nRUN apt-get update && apt-get install -y git"

[vars]
repo_name = "arc"
repo_url = "https://github.com/qltysh/arc"

[[hooks]]
event = "stage_start"
command = "./scripts/pre-check.sh"
blocking = true
sandbox = false

[[hooks]]
event = "run_complete"
command = "echo done"
```

## Sections

### `[llm]`

Override the default model and provider for all nodes that don't have an explicit model assigned via a [stylesheet](/workflows/stylesheets).

```toml title="run.toml"
[llm]
model = "claude-sonnet-4-5"
provider = "anthropic"
```

| Field | Description |
|---|---|
| `model` | Model ID or alias (e.g. `claude-sonnet-4-5`, `opus`, `gemini-pro`). See [Models](/core-concepts/models). |
| `provider` | Provider name: `anthropic`, `openai`, `gemini`, `kimi`, `zai`, `minimax`, `inception`. |

#### `[llm.fallbacks]`

Map each provider to an ordered list of fallback providers. When the primary provider is unavailable, Arc tries the fallbacks in order:

```toml title="run.toml"
[llm.fallbacks]
anthropic = ["gemini", "openai"]
gemini = ["anthropic", "openai"]
```

### `[setup]`

Shell commands to run before the workflow starts. Use this to clone repositories, install dependencies, or prepare the environment.

```toml title="run.toml"
[setup]
commands = ["pip install -r requirements.txt", "npm install"]
timeout_ms = 60000
```

| Field | Description |
|---|---|
| `commands` | List of shell commands, executed sequentially via `sh -c`. |
| `timeout_ms` | Per-command timeout in milliseconds. Default: `300000` (5 minutes). |

Each command must exit with status 0. If any command fails or times out, the run aborts before the workflow starts.

### `[sandbox]`

Configure how agent tools (bash, file edits) are executed.

```toml title="run.toml"
[sandbox]
provider = "docker"
preserve = true
```

| Field | Description |
|---|---|
| `provider` | Sandbox mode: `local` (default), `docker`, or `daytona`. |
| `preserve` | When `true`, keep the sandbox alive after the run finishes. Useful for debugging. |

#### `[sandbox.daytona]`

Additional settings when using the Daytona cloud sandbox:

```toml title="run.toml"
[sandbox.daytona]
auto_stop_interval = 60

[sandbox.daytona.labels]
project = "arc"
env = "staging"

[sandbox.daytona.snapshot]
name = "my-snapshot"
cpu = 4
memory = 8
disk = 20
dockerfile = "FROM rust:1.85-slim-bookworm\nRUN apt-get update"
```

| Field | Description |
|---|---|
| `auto_stop_interval` | Minutes of inactivity before the sandbox auto-stops. |
| `labels` | Key-value labels attached to the sandbox for filtering and identification. |
| `snapshot.name` | Snapshot name to create or use for the sandbox. |
| `snapshot.cpu` | CPU cores for the snapshot. |
| `snapshot.memory` | Memory in GB for the snapshot. |
| `snapshot.disk` | Disk in GB for the snapshot. |
| `snapshot.dockerfile` | Dockerfile content for building the snapshot image. |
| `network` | Network access mode: `"allow_all"` (default), `"block"`, or `{ allow_list = ["..."] }`. See [Sandboxing](/administration/sandboxing#network-access-control). |

### `[vars]`

Define variables that are expanded into the DOT source before the graph is parsed. See [Variables](/workflows/variables) for the full reference.

```toml title="run.toml"
[vars]
repo_name = "arc"
repo_url = "https://github.com/qltysh/arc"
language = "rust"
```

Variables can be used anywhere in the DOT file with `$name` syntax:

```dot title="c-i.dot"
digraph CI {
    graph [goal="Run tests for $repo_name"]
    clone [shape=parallelogram, script="git clone $repo_url repo"]
    test  [label="Test", prompt="Run the $language test suite."]
}
```

If a `$variable` in the DOT file has no matching entry in `[vars]`, Arc raises an error immediately. A bare `$` not followed by an identifier (e.g. `costs $5`) is left as-is.

### `[[hooks]]`

Define hooks that run in response to lifecycle events. Each hook is a TOML array entry:

```toml title="run.toml"
[[hooks]]
name = "pre-check"
event = "stage_start"
command = "./scripts/pre-check.sh"
matcher = "agent_loop"
blocking = true
timeout_ms = 30000
sandbox = false
```

| Field | Description |
|---|---|
| `name` | Optional display name for the hook. |
| `event` | Lifecycle event: `run_start`, `run_complete`, `stage_start`, `stage_complete`. |
| `command` | Shell command to execute (shorthand for `type = "command"`). |
| `matcher` | Regex matched against node ID or handler type. Limits which stages trigger this hook. |
| `blocking` | Whether the hook must complete before execution continues. Defaults vary by event. |
| `timeout_ms` | Hook timeout in milliseconds. Default: `60000` (60s). |
| `sandbox` | Run inside the sandbox (`true`, default) or on the host (`false`). |

See [Hooks](/agents/hooks) for hook types beyond simple commands (HTTP, prompt, agent).

## Top-level fields

In addition to the sections above, two optional top-level fields are available:

| Field | Description |
|---|---|
| `directory` | Working directory for the run. Defaults to the current directory. |

## Graph path resolution

The `graph` path is resolved relative to the TOML file's parent directory, not the current working directory. This means a run config and its workflow can live side by side:

```
project/
  runs/
    ci.toml       # graph = "ci.dot"
    ci.dot
```

Absolute paths are used as-is.

## Precedence

Settings can come from multiple sources. Arc resolves them in this order (first match wins):

| Source | Priority |
|---|---|
| Node-level [stylesheet](/workflows/stylesheets) | Highest |
| Run config TOML | |
| CLI flags (`--model`, `--provider`, `--sandbox`) | |
| Server defaults (`~/.arc/server.toml`) | |
| DOT graph attributes (`default_model`, `default_provider`) | |
| Built-in defaults | Lowest |

<Note>
For model and provider specifically, the precedence is: CLI flags > TOML config > server defaults > DOT graph attributes > built-in defaults. Stylesheet rules on individual nodes always take priority over all of these.
</Note>

### Server defaults

When running via `arc serve`, the server config at `~/.arc/server.toml` can set default values for `[llm]`, `[setup]`, `[sandbox]`, and `[vars]`. These defaults are applied to every run unless the run config overrides them.

For variables, defaults and run config are **merged** — the run config wins on key collisions:

```toml
# ~/.arc/server.toml
[vars]
default_key = "from_server"
shared = "from_server"

# run.toml
[vars]
shared = "from_run"       # wins
task_key = "from_run"
```

The same merge behavior applies to Daytona labels. All other fields use simple "first non-empty wins" precedence.

## Validation

Arc validates the run config when it loads:

- **Version check** — Only `version = 1` is accepted. Other versions are rejected immediately.
- **Required fields** — `version`, `goal`, and `graph` are all required. Missing any of them is an error.
- **Unknown fields** — Extra fields not listed above are rejected (`deny_unknown_fields`).
- **Variable check** — Any `$variable` in the DOT file without a matching `[vars]` entry produces an error.

Use `--preflight` to validate a run config without executing it:

```bash
arc run start run.toml --preflight
```