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browser_resize

Read-only

Resize browser windows to specific dimensions for testing or content layout adjustments. Set width and height parameters to control viewport size.

Instructions

Resize the browser window

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
widthYesWidth of the browser window
heightYesHeight of the browser window

Implementation Reference

  • The handler function for the 'browser_resize' tool. It adds code to resize the viewport and waits for completion by calling page.setViewportSize with the provided width and height.
    handle: async (tab, params, response) => {
      response.addCode(`await page.setViewportSize({ width: ${params.width}, height: ${params.height} });`);
    
      await tab.waitForCompletion(async () => {
        await tab.page.setViewportSize({ width: params.width, height: params.height });
      });
    },
  • The schema definition for the 'browser_resize' tool, specifying the name, title, description, input schema (width and height as numbers), and type as readOnly.
    schema: {
      name: 'browser_resize',
      title: 'Resize browser window',
      description: 'Resize the browser window',
      inputSchema: z.object({
        width: z.number().describe('Width of the browser window'),
        height: z.number().describe('Height of the browser window'),
      }),
      type: 'readOnly',
    },
  • The full tool definition and registration using defineTabTool, which includes schema and handler. This tool is exported and included in the allTools array in src/tools.ts.
    const resize = defineTabTool({
      capability: 'core',
      schema: {
        name: 'browser_resize',
        title: 'Resize browser window',
        description: 'Resize the browser window',
        inputSchema: z.object({
          width: z.number().describe('Width of the browser window'),
          height: z.number().describe('Height of the browser window'),
        }),
        type: 'readOnly',
      },
    
      handle: async (tab, params, response) => {
        response.addCode(`await page.setViewportSize({ width: ${params.width}, height: ${params.height} });`);
    
        await tab.waitForCompletion(async () => {
          await tab.page.setViewportSize({ width: params.width, height: params.height });
        });
      },
    });
Behavior3/5

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

Annotations already provide readOnlyHint=true, openWorldHint=true, and destructiveHint=false, indicating it's a safe, non-destructive operation. The description adds no behavioral context beyond this, such as whether it affects the current tab or all tabs, or if there are constraints like minimum/maximum dimensions. It doesn't contradict annotations, but offers minimal extra value.

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 a single, direct sentence with zero wasted words. It's front-loaded and efficiently conveys the core purpose without unnecessary elaboration, making it easy for an agent to parse quickly.

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

Completeness3/5

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

Given the tool's simplicity (2 parameters, 100% schema coverage, no output schema) and annotations covering safety, the description is minimally adequate. However, it lacks context on integration with sibling tools or operational details, which could help in more complex scenarios. It meets basic needs but doesn't fully leverage the opportunity for completeness.

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

Parameters3/5

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

Schema description coverage is 100%, with clear descriptions for width and height parameters. The description doesn't add any semantic details beyond the schema, such as unit explanations (e.g., pixels) or practical constraints. Baseline 3 is appropriate since the schema fully documents the parameters.

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 'Resize the browser window' clearly states the action (resize) and resource (browser window), which is specific and unambiguous. However, it doesn't explicitly differentiate from sibling tools like browser_tab_new or browser_tab_select, which also involve browser window management but for different purposes.

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

Usage Guidelines2/5

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

The description provides no guidance on when to use this tool versus alternatives. It doesn't mention prerequisites (e.g., needing an active browser session), exclusions, or related tools for similar tasks, leaving the agent to infer usage from context alone.

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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