canvas

name	canvas
description	Instructions for rendering rich A2UI canvas elements to the chat interface. Auto-injected for web UI sessions.
category	core
triggers	canvas, ui, interface, form, a2ui, interactive
alwaysApply	true
injectionFormat	content
metadata	{"gobby":{"audience":"all","sources":["claude_sdk_web_chat","gemini_sdk_web_chat"]}}

Canvas Frontend Integration

When interacting with a user in the web chat interface, you can render rich interactive elements (forms, layouts, status cards) directly in their chat view using the Canvas tools.

When to use the Canvas

Use the canvas when you need to:

• Collect multiple pieces of structured input (e.g., a configuration form with checkboxes and text fields).
• Present a complex dashboard or interactive summary.
• Display a rich card with actionable buttons instead of a plain text list.
• Keep the chat clean by replacing long text prompts with a visual form.

Available Tools

The canvas tools are available through the gobby-canvas (or internal MCP) server:

1. render_surface: Renders a declarative JSON UI. Pass a flat components map (keyed by component ID), a root_id, and an initial data_model.
2. update_surface: Patches an existing canvas with new components or data.
3. wait_for_interaction: Pauses execution until the user interacts with the canvas (e.g., clicking a submit button). Returns the action name and the updated data model.
4. close_canvas: Manually closes/completes the canvas when interaction is done.
5. canvas_present: Present a local HTML file in the Canvas panel sandbox (iframe).

A2UI Component System

A2UI is a declarative JSON layout system. Components are defined in a flat surface map keyed by unique component IDs. Parent components reference children by ID via children: { explicitList: ["child-id-1", "child-id-2"] }.

Key components:

• Layouts: Column, Row, Card, List
• Inputs: TextField, CheckBox
• Displays: Text, Badge, Icon, Image
• Actions: Button

Data Binding

Text and labels use BoundValue objects:

• Literal text: { "literalString": "Hello" }
• Data-bound: { "path": "user/name" } (resolves from the data_model)

Actions

Buttons define actions as: "actions": [{ "name": "action_name", "context": { "key": { "path": "field/path" } } }]

Example Workflow

// 1. Define a flat component surface map
{
  "components": {
    "root": {
      "type": "Card",
      "label": { "literalString": "Configuration" },
      "children": { "explicitList": ["username-field", "save-btn"] }
    },
    "username-field": {
      "type": "TextField",
      "label": { "literalString": "Username" },
      "value": { "path": "username" }
    },
     
       
          
                  
    
  
   
      
   
   

# 1. Render the surface
result = call_tool("gobby-canvas", "render_surface", {
    "components": {
        "root": {
            "type": "Card",
            "label": {"literalString": "Configuration"},
            "children": {"explicitList": ["username-field", "save-btn"]}
        },
        "username-field": {
            "type": "TextField",
            "label": {"literalString": "Username"},
            "value": {"path": "username"}
        },
        "save-btn": {
            "type": "Button",
            "label": {"literalString": "Save"},
            "actions": [{"name": "save_config", "context": {"username": {"path": "username"}}}]
        }
    },
    "root_id": "root",
    "data_model": {"username": "admin"},
    "blocking": True,
    "timeout": 300
})

# blocking=True means render_surface waits for interaction and returns the result directly
canvas_id = result.get("canvas_id")
action = result.get("action")

 action  action.get() == :
    username = action.get(, {}).get()
    

    
    call_tool(, , {: canvas_id})