Playwright MCP

browser_resize

Destructive

Adjust browser window dimensions for testing responsive web designs or capturing specific viewport states during automation.

Instructions

Resize the browser window

Input Schema

TableJSON Schema

Name	Required	Description	Default
`width`	Yes	Width of the browser window
`height`	Yes	Height of the browser window

Implementation Reference

src/tools/common.ts:54-72 (handler)

The handler function for the 'browser_resize' tool. It resizes the viewport size of the current browser tab using the provided width and height parameters, generates a code snippet representing the action, defines an action to execute the resize, and returns the necessary metadata for execution.

handle: async (context, params) => {
  const tab = context.currentTabOrDie();

  const code = [
    `// Resize browser window to ${params.width}x${params.height}`,
    `await page.setViewportSize({ width: ${params.width}, height: ${params.height} });`
  ];

  const action = async () => {
    await tab.page.setViewportSize({ width: params.width, height: params.height });
  };

  return {
    code,
    action,
    captureSnapshot,
    waitForNetwork: true
  };
},

src/tools/common.ts:43-52 (schema)

The schema definition for the 'browser_resize' tool, including name, title, description, input schema validating 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',
},

src/tools.ts:35-50 (registration)

Registration of the browser_resize tool as part of the snapshotTools array, imported via common(true) which includes the resize tool.

export const snapshotTools: Tool<any>[] = [
  ...common(true),
  ...console,
  ...dialogs(true),
  ...files(true),
  ...install,
  ...keyboard(true),
  ...navigate(true),
  ...network,
  ...pdf,
  ...screenshot,
  ...snapshot,
  ...tabs(true),
  ...testing,
  ...wait(true),
];

src/tools.ts:52-66 (registration)

Registration of the browser_resize tool as part of the visionTools array, imported via common(false) which includes the resize tool.

export const visionTools: Tool<any>[] = [
  ...common(false),
  ...console,
  ...dialogs(false),
  ...files(false),
  ...install,
  ...keyboard(false),
  ...navigate(false),
  ...network,
  ...pdf,
  ...tabs(false),
  ...testing,
  ...vision,
  ...wait(false),
];

Tool Definition Quality

B3.3/5.0

Behavior3/5

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

Annotations already indicate destructiveHint=true (mutation) and readOnlyHint=false, so the agent knows this modifies state. The description adds no behavioral context beyond this, such as whether resizing affects page layout, requires specific permissions, or has side effects. With annotations covering the safety profile, a baseline 3 is appropriate as the description doesn't contradict but adds little 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, efficient sentence with zero waste. It's front-loaded and directly conveys the core function 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 moderate complexity (destructive operation with two parameters), annotations provide safety context, but there's no output schema. The description lacks details on return values (e.g., success confirmation) or error conditions, leaving gaps. It's minimally adequate but not fully complete for informed use.

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 parameter descriptions for width and height. The description adds no meaning beyond what the schema provides, such as unit explanations (pixels), valid ranges, or default behaviors. Since the schema does the heavy lifting, the baseline score of 3 is warranted.

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), making the purpose immediately understandable. It distinguishes from siblings like browser_close or browser_navigate by specifying the resize operation. However, it lacks explicit differentiation from tools like browser_snapshot that might also involve window dimensions, preventing a perfect score.

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., an active browser session), exclusions (e.g., not for mobile browsers), or comparisons to siblings like browser_take_screenshot for visual changes. This leaves the agent with minimal context for tool selection.

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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