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browser_screenshot

Capture screenshots of web pages or specific elements during penetration testing to document vulnerabilities and analyze web application security.

Instructions

Take a screenshot of the current page or a specific element

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
nameYesName for the screenshot
selectorNoCSS selector for element to screenshot
fullPageNoTake a full page screenshot (default: false)

Implementation Reference

  • Handler function for browser_screenshot tool: captures screenshot of page or element, encodes to base64, stores it, notifies resource change, returns success message and image content.
    case ToolName.BrowserScreenshot: {
      const fullPage = (args.fullPage === 'true');
    
      const screenshot = await (args.selector ?
        page.locator(args.selector).screenshot() :
        page.screenshot({ fullPage }));
      const base64Screenshot = screenshot.toString('base64');
    
      if (!base64Screenshot) {
        return {
          content: [{
            type: "text",
            text: args.selector ? `Element not found: ${args.selector}` : "Screenshot failed",
          }],
          isError: true,
        };
      }
    
      screenshots.set(args.name, base64Screenshot);
      server.notification({
        method: "notifications/resources/list_changed",
      });
    
      return {
        content: [
          {
            type: "text",
            text: `Screenshot '${args.name}' taken`,
          } as TextContent,
          {
            type: "image",
              data: base64Screenshot,
              mimeType: "image/png",
            } as ImageContent,
          ],
        isError: false,
      };
    }
  • index.ts:50-62 (registration)
    Tool registration in TOOLS array, including name, description, and input schema for browser_screenshot.
    {
      name: ToolName.BrowserScreenshot,
      description: "Take a screenshot of the current page or a specific element",
      inputSchema: {
        type: "object",
        properties: {
          name: { type: "string", description: "Name for the screenshot" },
          selector: { type: "string", description: "CSS selector for element to screenshot" },
          fullPage: { type: "boolean", description: "Take a full page screenshot (default: false)", default: false },
        },
        required: ["name"],
      },
    },
  • Input schema defining parameters for the browser_screenshot tool: name (required), selector (optional), fullPage (optional boolean).
    inputSchema: {
      type: "object",
      properties: {
        name: { type: "string", description: "Name for the screenshot" },
        selector: { type: "string", description: "CSS selector for element to screenshot" },
        fullPage: { type: "boolean", description: "Take a full page screenshot (default: false)", default: false },
      },
      required: ["name"],
    },
  • index.ts:841-842 (registration)
    Registers the list of tools (including browser_screenshot) with the MCP server via ListToolsRequestSchema handler.
      tools: TOOLS,
    }));
Behavior2/5

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It states what the tool does but lacks critical behavioral details: it doesn't specify output format (e.g., image file, base64), error handling (e.g., what happens if selector isn't found), or side effects (e.g., whether it pauses page interaction). This leaves significant gaps for an agent to understand how to use it effectively.

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, clear sentence with zero wasted words. It's front-loaded with the core action and target, making it easy to parse quickly. Every word earns its place by conveying essential information.

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

Completeness2/5

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

Given the tool's moderate complexity (screenshot functionality with three parameters) and the absence of both annotations and an output schema, the description is incomplete. It fails to address key contextual aspects like what the tool returns, how errors are handled, or dependencies on other tools (e.g., browser_navigate). This makes it inadequate for safe and effective use by an agent.

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?

The input schema has 100% description coverage, so the schema already documents all parameters thoroughly. The description adds no additional meaning beyond what's in the schema—it doesn't explain parameter interactions (e.g., how selector and fullPage relate) or provide examples. This meets the baseline for high schema coverage.

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 clearly states the action ('take a screenshot') and the target ('current page or a specific element'), which is specific and unambiguous. However, it doesn't explicitly differentiate from sibling tools like browser_evaluate or browser_navigate, which serve different purposes but are also page-related operations.

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 a page loaded first), exclusions, or comparisons to other screenshot-related tools that might not exist in the sibling list.

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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