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139 lines
4.9 KiB
Text
139 lines
4.9 KiB
Text
---
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title: "Model Stylesheets"
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description: "Assign LLM models to workflow nodes using CSS-like rules"
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---
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Model stylesheets let you assign LLM models, providers, and settings to workflow nodes using a CSS-like syntax. Instead of hardcoding a model on every node, you write a set of rules that target nodes by ID, class, shape, or a universal wildcard — and Fabro applies them by specificity.
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## Defining a stylesheet
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Stylesheets are set in the `model_stylesheet` graph attribute:
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```dot title="example.fabro"
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digraph Example {
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graph [
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goal="Build and review a utility function",
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model_stylesheet="
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* { model: claude-haiku-4-5;}
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.coding { model: claude-sonnet-4-5; reasoning_effort: high; }
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#review { model: gemini-3.1-pro-preview;}
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"
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]
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start [shape=Mdiamond, label="Start"]
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exit [shape=Msquare, label="Exit"]
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spec [label="Write Spec"]
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implement [label="Implement", class="coding"]
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test [label="Write Tests", class="coding"]
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review [label="Code Review"]
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start -> spec -> implement -> test -> review -> exit
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}
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```
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In this example:
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- **spec** gets Haiku (matches `*`)
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- **implement** and **test** get Sonnet with high reasoning (match `.coding`)
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- **review** gets Gemini Pro (matches `#review`)
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## Selectors
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Each rule starts with a selector that determines which nodes it applies to:
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| Selector | Syntax | Matches | Specificity |
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|---|---|---|---|
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| Universal | `*` | All nodes | 0 |
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| Shape | `box`, `tab`, `hexagon`, etc. | Nodes with that Graphviz shape | 1 |
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| Class | `.classname` | Nodes with `class="classname"` | 2 |
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| ID | `#nodeid` | The node with that specific ID | 3 |
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### Assigning classes
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Set the `class` attribute on a node to target it with class selectors. Separate multiple classes with spaces:
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```dot
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implement [label="Implement", class="coding critical"]
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```
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This node matches both `.coding` and `.critical` rules.
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## Properties
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Stylesheets support four properties:
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| Property | Description | Example |
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|---|---|---|
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| `model` | Model ID or alias | `claude-sonnet-4-5`, `opus`, `gemini-pro` |
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| `provider` | Provider name (optional — auto-inferred from the model catalog when omitted) | `anthropic`, `openai`, `gemini` |
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| `reasoning_effort` | Reasoning effort level | `low`, `medium`, `high` |
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| `speed` | Output speed mode. `fast` enables Anthropic's fast mode for up to 2.5x faster output at higher cost. | `fast` |
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| `backend` | Agent execution backend — `api` (default) runs Fabro's own tool loop, `cli` delegates to a legacy external CLI tool, and `acp` runs an Agent Client Protocol stdio agent in the active sandbox. See [Backends](/core-concepts/agents#backends). | `api`, `cli`, `acp` |
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See [Models](/core-concepts/models) for the full list of model IDs and aliases.
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## Specificity and cascading
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When multiple rules match the same node, the rule with the **highest specificity** wins. This follows the same principle as CSS:
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```
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* (0) < shape (1) < .class (2) < #id (3)
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```
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For example:
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```
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* { model: claude-haiku-4-5; }
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.coding { model: claude-sonnet-4-5; }
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#review { model: gpt-5.4; }
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```
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A node with `id="review"` and `class="coding"` gets `gpt-5.4` because `#id` (specificity 3) beats `.class` (specificity 2).
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If two rules have the same specificity, the **last one** in the stylesheet wins.
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## Explicit attributes override stylesheets
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A model set directly on a node attribute always takes precedence over stylesheets, regardless of specificity:
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```dot
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implement [label="Implement", class="coding", model="claude-opus-4-6"]
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```
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Even if `.coding` sets `model: claude-sonnet-4-5`, this node uses Opus because the explicit attribute wins.
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## Syntax reference
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The stylesheet syntax is a simplified subset of CSS:
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```
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selector { property: value; property: value; }
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```
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- Selectors: `*`, `shape`, `.class`, `#id`
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- Properties and values are separated by `:`
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- Declarations are separated by `;`
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- Whitespace is flexible — newlines and indentation are ignored
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- CSS block comments (`/* ... */`) can appear between tokens and are ignored
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- Comments close at the first `*/` and do not nest; an unterminated comment is a syntax error
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- `//` starts a comment in the surrounding workflow file, but not inside a stylesheet
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### Full example
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```
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/* Use a fast model by default. */
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* { model: claude-haiku-4-5;reasoning_effort: low; }
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box { reasoning_effort: high; }
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tab { reasoning_effort: low; }
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.coding { model: claude-sonnet-4-5;reasoning_effort: high; }
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.review { model: gemini-3.1-pro-preview;}
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#final_check { model: claude-opus-4-6;reasoning_effort: high; }
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```
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This stylesheet:
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- Defaults everything to Haiku with low reasoning
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- Overrides all agent nodes (`box` shape) to high reasoning
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- Keeps prompt nodes (`tab` shape) at low reasoning
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- Routes `.coding` nodes to Sonnet
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- Routes `.review` nodes to Gemini for independent critique
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- Routes the `final_check` node to Opus for maximum quality
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