Tool UI Skill

Status: Production Ready Last Updated: 2026-01-21 Dependencies: @/components/chat/renderers

Quick Start

To add a custom UI for a new tool:

/add-tool-ui my-tool-name

Or follow the manual steps below.

Step 1: Create the Component

Create a new card component in src/components/ai-elements/:

// src/components/ai-elements/my-tool-card.tsx
'use client';

import type { ComponentProps } from 'react';
import { cn } from '@/lib/utils';

export interface MyToolData {
    // Match your tool's outputSchema
    result: string;
    value: number;
}

interface MyToolCardProps extends ComponentProps<'div'> {
    data: MyToolData;
}

export function MyToolCard({ data, className, ...props }: MyToolCardProps) {
    return (
        <div className={cn('not-prose mb-4 w-full rounded-md border p-4', className)} {...props}>
            <span className="font-medium">{data.result}</span>
            <span className="text-muted-foreground">{data.value}</span>
        </div>
    );
}

// Type guard - REQUIRED for registry
export function isMyToolData(data: unknown): data is MyToolData {
    if (!data || typeof data !== 'object') return false;
    const d = data as Record<string, unknown>;
    return typeof d.result === 'string' && typeof d.value === 'number';
}

Critical: The type guard function is required for the registry to validate output data.

Step 2: Register in the Registry

Add registration to src/components/chat/renderers/index.ts:

// At the imports section
import { MyToolCard, isMyToolData } from '@/components/ai-elements/my-tool-card';

// After the existing toolUIRegistry.register() calls
toolUIRegistry.register({
    toolIds: ['my-tool-id'],        // Must match tool's `id` in Mastra
    Component: MyToolCard,
    isValidOutput: isMyToolData,
});

Note: toolIds is an array - some tools have different IDs in different contexts (e.g., ['get-weather', 'weatherTool']).

Step 3: Done

The component now automatically renders in:

• ✅ Streaming via network-renderer.tsx
• ✅ History via dynamic-tool-renderer.tsx

Registry API

interface ToolUIRegistration<TOutput = unknown> {
    toolIds: string[];                              // Tool ID(s)
    Component: FC<{ data: TOutput }>;               // React component
    isValidOutput: (output: unknown) => output is TOutput;  // Type guard
}

// Register
toolUIRegistry.register(registration);

// Check if tool has custom UI
toolUIRegistry.hasCustomUI('tool-id');  // boolean

// Get component for output
toolUIRegistry.getComponent('tool-id', output);  
// Returns: { Component, data } | null

How It Works

flowchart TD
    subgraph Registry["ToolUIRegistry"]
        Map["Map<toolId, Registration>"]
    end
    
    subgraph Streaming["Streaming Context"]
        NR["network-renderer.tsx"]
        Extract["extractToolUIFromNetwork()"]
        NR --> Extract --> Map
    end
    
    subgraph History["History Context"]
        DTR["dynamic-tool-renderer.tsx"]
        Lookup["getComponent()"]
        DTR --> Lookup --> Map
    end
    
    Map --> Component["Your Component"]

Troubleshooting

Component not rendering during streaming

1. Check the tool ID matches exactly what Mastra uses
2. Verify the tool is in an agent that uses networkRoute()
3. Check toolResults structure in network steps

Component not rendering in history

1. Check toolName in childMessages matches registered ID
2. Verify isValidOutput returns true for the data
3. Check console for validation errors

Finding the correct tool ID

Look at your Mastra tool definition:

// src/mastra/tools/my-tool.ts
export const myTool = createTool({
    id: 'my-tool-id',  // <-- This is the ID to register
    // ...
});

Example: WeatherCard

Reference implementation at:

• Component: src/components/ai-elements/weather-card.tsx
• Tool: src/mastra/tools/weather-tool.ts
• Registration: src/components/chat/renderers/index.ts