Model Stylesheets

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.

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)

Template stylesheets

The root graph’s model_stylesheet is a MiniJinja template. It can read typed run inputs and server-managed variables through inputs and vars:

variable-effort.fabro

digraph Review {
    graph [
        model_stylesheet="
            * { reasoning_effort: low; }

            {% if inputs.effort == 'deep' %}
            .variable-effort { reasoning_effort: high; }
            {% elif inputs.effort == 'balanced' %}
            .variable-effort { reasoning_effort: medium; }
            {% endif %}
        "
    ]

    triage [prompt="Triage the change"]
    review [prompt="Review the change", class="variable-effort"]
}

Stylesheet templates support expressions, conditionals, loops, filters, macros, {% set %}, and normal local values such as loop. They do not expose goal, env, or secrets. Fabro renders a stylesheet once. If an input or variable contains {{ ... }} or {% ... %}, that text stays literal. Fabro does not render it again. Template output is not escaped as stylesheet syntax. Map user-facing choices to fixed declarations instead of inserting unrestricted text directly:

model_stylesheet="
    {% set efforts = {'quick': 'low', 'thorough': 'high'} %}
    .review { reasoning_effort: {{ efforts[inputs.review_mode] }}; }
"

Use single quotes inside MiniJinja expressions when possible. A double quote must follow normal DOT string escaping because the surrounding graph attribute uses double quotes. MiniJinja braces need no extra escaping inside the quoted DOT attribute. Static template includes are supported and resolve relative to the workflow template root:

graph [model_stylesheet="{% include 'styles/models.partial' %}"]

Include paths must be literal. Dynamic or root-escaping include paths fail validation. model_stylesheet does not support the @file shorthand. Fabro uses this order:

Parse the DOT source.
Expand workflow imports and supported file references.
Render the root model_stylesheet with { inputs, vars }.
Parse and apply the rendered stylesheet.
Resolve model and provider selectors.
Validate the transformed graph.

A model_stylesheet on an imported graph is ignored and produces an imported_model_stylesheet_ignored warning. Put the stylesheet on the root graph. A root stylesheet can target imported nodes by their generated IDs, classes, or shapes. If an input or variable is unavailable, fabro validate reports template_undefined_variable. It skips stylesheet syntax and model checks for that validation pass. Run-style commands treat the same diagnostic as an error before they create or start a run.

Selectors

Each rule starts with a selector that determines which nodes it applies to:

Selector	Syntax	Matches	Specificity
Universal	`*`	All nodes	0
Shape	`box`, `tab`, `hexagon`, etc.	Nodes with that Graphviz shape	1
Class	`.classname`	Nodes with `class="classname"`	2
ID	`#nodeid`	The node with that specific ID	3

Assigning classes

Set the class attribute on a node to target it with class selectors. Separate multiple classes with spaces:

implement [label="Implement", class="coding critical"]

This node matches both .coding and .critical rules.

Properties

Stylesheets support five properties:

Property	Description	Example
`model`	Model ID or alias	`claude-sonnet-4-5`, `opus`, `gemini-pro`
`provider`	Provider name (optional — auto-inferred from the model catalog when omitted)	`anthropic`, `openai`, `gemini`
`reasoning_effort`	Reasoning effort level	`low`, `medium`, `high`
`speed`	Output speed mode. `fast` enables Anthropic’s fast mode for up to 2.5x faster output at higher cost.	`fast`
`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.	`api`, `cli`, `acp`

See Models for the full list of model IDs and aliases.

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-5.4; }

A node with id="review" and class="coding" gets gpt-5.4 because #id (specificity 3) beats .class (specificity 2). If two rules have the same specificity, the last one in the stylesheet wins.

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.

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 block comments (/* ... */) can appear between tokens and are ignored
Comments close at the first */ and do not nest; an unterminated comment is a syntax error
// starts a comment in the surrounding workflow file, but not inside a stylesheet

Full example

/* Use a fast model by default. */
*            { 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

Getting Started

Core Concepts

Defining Workflows

Executing Workflows

Human Tools

Agents

Integrations

Reference

Model Stylesheets

Defining a stylesheet

Template stylesheets

Selectors

Assigning classes

Properties

Specificity and cascading

Explicit attributes override stylesheets

Syntax reference

Full example

​Defining a stylesheet

​Template stylesheets

​Selectors

​Assigning classes

​Properties

​Specificity and cascading

​Explicit attributes override stylesheets

​Syntax reference

​Full example

Defining a stylesheet

Template stylesheets

Selectors

Assigning classes

Properties

Specificity and cascading

Explicit attributes override stylesheets

Syntax reference

Full example