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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

Stylesheets are set in the model_stylesheet graph attribute:
example.fabro
digraph Example {
    graph [
        goal="Build and review a utility function",
        model_stylesheet="
            *        { model: claude-haiku-4-5;}
            .coding  { model: claude-sonnet-4-5; reasoning_effort: high; }
            #review  { model: gemini-3.1-pro-preview;}
        "
    ]

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

    spec      [label="Write Spec"]
    implement [label="Implement", class="coding"]
    test      [label="Write Tests", class="coding"]
    review    [label="Code Review"]

    start -> spec -> implement -> test -> review -> exit
}
In this example:
  • spec gets Haiku (matches *)
  • implement and test get Sonnet with high reasoning (match .coding)
  • review gets Gemini Pro (matches #review)

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Selectors

Each rule starts with a selector that determines which nodes it applies to:
SelectorSyntaxMatchesSpecificity
Universal*All nodes0
Shapebox, tab, hexagon, etc.Nodes with that Graphviz shape1
Class.classnameNodes with class="classname"2
ID#nodeidThe node with that specific ID3

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Assigning classes

Set the class attribute on a node to target it with class selectors. Multiple classes are space-separated: 
implement [label="Implement", class="coding critical"]
This node matches both .coding and .critical rules.

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Properties

Stylesheets support four properties:
PropertyDescriptionExample
modelModel ID or aliasclaude-sonnet-4-5, opus, gemini-pro
providerProvider name (optional — auto-inferred from the model catalog when omitted)anthropic, openai, gemini
reasoning_effortReasoning effort levellow, medium, high
backendAgent execution backend — api (default) runs Fabro’s own tool loop, cli delegates to an external CLI tool. See Backends.cli, api
See Models for the full list of model IDs and aliases.

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Specificity and cascading

When multiple rules match the same node, the rule with the highest specificity wins. This follows the same principle as CSS: 
* (0) < shape (1) < .class (2) < #id (3)
For example: 
*       { model: claude-haiku-4-5; }
.coding { model: claude-sonnet-4-5; }
#review { model: gpt-5.2; }
A node with id="review" and class="coding" gets gpt-5.2 because #id (specificity 3) beats .class (specificity 2). If two rules have the same specificity, the last one in the stylesheet wins.

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Explicit attributes override stylesheets

A model set directly on a node attribute always takes precedence over stylesheets, regardless of specificity: 
implement [label="Implement", class="coding", model="claude-opus-4-6"]
Even if .coding sets model: claude-sonnet-4-5, this node uses Opus because the explicit attribute wins.

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Syntax reference

The stylesheet syntax is a simplified subset of CSS: 
selector { property: value; property: value; }
  • Selectors: *, shape, .class, #id
  • Properties and values are separated by :
  • Declarations are separated by ;
  • Whitespace is flexible — newlines and indentation are ignored
  • CSS comments (/* ... */) are not supported

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Full example

*            { model: claude-haiku-4-5;reasoning_effort: low; }
box          { reasoning_effort: high; }
tab          { reasoning_effort: low; }
.coding      { model: claude-sonnet-4-5;reasoning_effort: high; }
.review      { model: gemini-3.1-pro-preview;}
#final_check { model: claude-opus-4-6;reasoning_effort: high; }
This stylesheet:
  • Defaults everything to Haiku with low reasoning
  • Overrides all agent nodes (box shape) to high reasoning
  • Keeps prompt nodes (tab shape) at low reasoning
  • Routes .coding nodes to Sonnet
  • Routes .review nodes to Gemini for independent critique
  • Routes the final_check node to Opus for maximum quality