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JustasMonkev

MCP Accessibility Scanner

by JustasMonkev
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TypeScript
Hybrid

browser_drag

Destructive

Enable drag-and-drop interactions between specified web elements to test accessibility and functionality during automated WCAG compliance scans using MCP Accessibility Scanner.

Instructions

Perform drag and drop between two elements

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
endElementYesHuman-readable target element description used to obtain the permission to interact with the element
endRefYesExact target element reference from the page snapshot
startElementYesHuman-readable source element description used to obtain the permission to interact with the element
startRefYesExact source element reference from the page snapshot

Implementation Reference

  • src/tools/snapshot.ts:165-178 (handler)
    Handler function for the browser_drag tool. It resolves locators for the start and end elements from the page snapshot, performs the drag operation using Playwright's dragTo method, waits for completion, and adds the corresponding code snippet to the response.
    handle: async (tab, params, response) => {
  response.setIncludeSnapshot();

  const [startLocator, endLocator] = await tab.refLocators([
    { ref: params.startRef, element: params.startElement },
    { ref: params.endRef, element: params.endElement },
  ]);

  await tab.waitForCompletion(async () => {
    await startLocator.dragTo(endLocator);
  });

  response.addCode(`await page.${await generateLocator(startLocator)}.dragTo(page.${await generateLocator(endLocator)});`);
},
  • src/tools/snapshot.ts:152-163 (schema)
    Schema definition for the browser_drag tool, specifying the input parameters for start and end elements (human-readable description and exact ref from snapshot), marked as destructive.
    schema: {
  name: 'browser_drag',
  title: 'Drag mouse',
  description: 'Perform drag and drop between two elements',
  inputSchema: z.object({
    startElement: z.string().describe('Human-readable source element description used to obtain the permission to interact with the element'),
    startRef: z.string().describe('Exact source element reference from the page snapshot'),
    endElement: z.string().describe('Human-readable target element description used to obtain the permission to interact with the element'),
    endRef: z.string().describe('Exact target element reference from the page snapshot'),
  }),
  type: 'destructive',
},
  • src/tools/snapshot.ts:229-236 (registration)
    The drag tool (browser_drag) is registered by being included in the default export array of tools from this module.
    export default [
  snapshot,
  click,
  drag,
  hover,
  selectOption,
  scanPage
];

Tool Definition Quality

B3.3/5.0
Behavior3/5

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

Annotations already declare destructiveHint=true and readOnlyHint=false, indicating this is a mutating operation. The description adds minimal behavioral context beyond this - it specifies the action involves two elements but doesn't describe what 'drag and drop' entails (e.g., visual feedback, timing, error conditions). No contradiction with annotations exists, but the description could better explain the destructive nature implied by the annotations.

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 that immediately conveys the core action. Every word earns its place - 'Perform' establishes it as an action tool, 'drag and drop' specifies the interaction type, and 'between two elements' clarifies the scope. No wasted words or redundant information.

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?

For a destructive browser interaction tool with no output schema, the description is minimally adequate. It identifies the action but lacks important context about how drag-and-drop works in this implementation, what visual feedback to expect, or how to handle failures. The annotations provide safety information, but the description could better prepare the agent for this mutating operation.

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?

With 100% schema description coverage, the input schema already fully documents all four parameters. The description adds no additional parameter information beyond implying there are 'two elements' (matching start/end parameters). This meets the baseline for high schema coverage but doesn't enhance understanding of parameter usage or relationships.

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 ('Perform drag and drop') and specifies the relationship ('between two elements'), which distinguishes it from simpler single-element interactions like browser_click or browser_hover. However, it doesn't explicitly differentiate from other complex interactions like browser_file_upload or browser_select_option, which might also involve multi-step 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 (like needing element references from browser_snapshot), nor does it explain when drag-and-drop is appropriate versus other interaction methods. The agent must 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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