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A2UI MCP Server

by mitsuru
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Update A2UI Components

a2ui_update_components
Idempotent

Update an A2UI surface by submitting a flat list of declarative components. Include a root entry to arrange layout, text, inputs, buttons, and images in real time.

Instructions

Add or update components on an A2UI surface.

Components are defined as a flat list with ID references. The component tree is built using the 'children' property.

IMPORTANT: You must include a component with id='root' as the entry point.

Available components:

  • Column: Vertical layout container (children: string[])

  • Row: Horizontal layout container (children: string[])

  • Card: Card container with optional title (children: string[], title?: string)

  • Text: Text display (text: string, style?: {...})

  • Button: Clickable button (label: string, variant?: 'primary'|'secondary'|'outlined', action?: string)

  • TextField: Input field (label: string, placeholder?: string, value?: string)

  • Image: Image display (src: string, alt?: string)

  • Divider: Horizontal line

  • Progress: Progress bar (value?: number 0-100, indeterminate?: boolean)

Example - Simple form: { "surface_id": "my_form", "components": [ { "id": "root", "component": "Column", "children": ["title", "name_field", "submit_btn"] }, { "id": "title", "component": "Text", "text": "Contact Form", "style": { "fontSize": 24, "fontWeight": "bold" } }, { "id": "name_field", "component": "TextField", "label": "Your Name", "placeholder": "Enter name..." }, { "id": "submit_btn", "component": "Button", "label": "Submit", "variant": "primary" } ] }

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
componentsYesArray of components. Must include a 'root' component.
surface_idYesSurface ID to update

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.0

TDQS

A4.1/5.0
Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations establish that the operation is non-read-only, non-destructive, and idempotent. The description supplements this by explaining how components are structured: a flat list with ID references, the root requirement, and tree construction via children. It does not disclose merge/replacement semantics for existing components or error behavior, but the provided detail is strong for safe invocation.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is long but every section earns its place: purpose, structural rule, component catalog, and example. The component list is scannable, the IMPORTANT note is appropriately emphasized, and the example demonstrates nesting without filler or redundancy.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the lack of an output schema and the mutation-oriented nature of the tool, the description covers all essential invocation details: required surface_id, component array shape, root requirement, and the full catalog of supported components. It does not explain what happens if the surface does not exist or whether existing components are replaced, but the annotations and schema cover the main risk profile sufficiently.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters5/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Although schema description coverage is 100%, the description goes well beyond it by mapping each component type to its applicable properties and providing a full JSON example. This per-component guidance resolves ambiguity that the generic schema property descriptions leave open, significantly improving correct parameter usage.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description opens with a specific verb and resource: 'Add or update components on an A2UI surface.' It also enumerates the exact component types and gives an example, making the tool's function easy to grasp. However, it does not explicitly differentiate itself from sibling tools like a2ui_create_surface or a2ui_update_data.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description clearly implies when to use the tool: when adding or updating UI components on an A2UI surface. It also provides critical usage rules such as the mandatory 'root' component and the flat-list/children structure. It stops short of saying 'use this instead of X' or listing exclusions relative to siblings, so the guidance is implied rather than explicit.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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