---
title: "Variables"
description: "Using variables in workflows"
---

Fabro supports `$variable` placeholders that let you parameterize workflows without editing the Graphviz file.

## Run config inputs

Define inputs in the `[run.inputs]` section of a run config TOML file:

```toml title="run.toml"
_version = 1

[workflow]
graph = "check.fabro"

[run]
goal = "Run tests for $repo_name"

[run.inputs]
repo_name = "fabro"
repo_url = "https://github.com/fabro-sh/fabro"
language = "rust"
```

These inputs are expanded into the Graphviz source **before** the graph is parsed. You can use `$variable` anywhere in the Graphviz file — goals, prompts, labels, scripts, or any other attribute:

```dot title="check.fabro"
digraph Check {
    graph [goal="Run tests for $repo_name"]

    start [shape=Mdiamond, label="Start"]
    exit  [shape=Msquare, label="Exit"]

    clone [label="Clone", shape=parallelogram, script="git clone $repo_url repo"]
    test  [label="Test", prompt="Run the $language test suite in the repo/ directory."]

    start -> clone -> test -> exit
}
```

When launched with `fabro run run.toml`, Fabro replaces `$repo_name`, `$repo_url`, and `$language` with their values before parsing the graph.

### Undefined variables

If a `$variable` in the Graphviz file has no matching entry in `[run.inputs]`, Fabro raises an error. This catches typos early — a misspelled `$langauge` fails immediately rather than passing a literal `$langauge` to the LLM.

### Escaping `$`

To include a literal `$` in the output, write `$$`:

```dot
test [prompt="The env var is $$HOME"]
```

This produces `The env var is $HOME` without treating `$HOME` as a variable reference. A bare `$` not followed by an identifier character (e.g. `costs $5`) does not need escaping.

## The `$goal` variable

Inside agent and prompt node prompts, Fabro automatically expands `$goal` to the workflow's `goal` attribute. This happens at runtime, after graph parsing:

```dot title="example.fabro"
digraph Example {
    graph [goal="Implement the login feature"]

    plan [label="Plan", prompt="Create a plan for: $goal"]
}
```

The plan node's prompt becomes `"Create a plan for: Implement the login feature"`.

## Input merging

`[run.inputs]` intentionally replaces the inherited map wholesale rather than merging by key. Whichever layer has the highest precedence and sets `[run.inputs]` wins its entire map — lower-precedence inputs do not show through.

| Source | Priority |
|---|---|
| CLI flags (`-V key=value`, repeated) | Highest |
| `workflow.toml` `[run.inputs]` | |
| `fabro.toml` `[run.inputs]` | |
| `~/.fabro/settings.toml` `[run.inputs]` | Lowest |

If you need per-key overrides on top of inherited defaults, set each input explicitly in the winning layer.