app-screen-mcp

by xmuweili

Overview Schema Source Related Servers Discussions Admin

TypeScript

Local

tap

Tap at specific coordinates on iOS Simulator screens to automate testing and interaction tasks for mobile applications.

Instructions

Tap at specific (x, y) coordinates on the simulator screen

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "x": "<x>",
      "y": "<y>"
    },
    "name": "tap"
  }
}

Input Schema

Name	Required	Description
`x`	Yes	X coordinate in points
`y`	Yes	Y coordinate in points
`udid`	No	Simulator UDID (optional, defaults to booted simulator)

Implementation Reference

src/index.ts:749-759 (handler)

Implementation of the 'tap' tool handler that uses the 'idb' CLI to execute a tap at specific coordinates.

private async tap(x: number, y: number, udid?: string) {
  const target = await resolveUdid(udid);
  try {
    await execAsync(`idb ui tap --udid ${target} ${x} ${y}`);
    return {
      content: [{ type: 'text', text: `Tapped (${x}, ${y}) on ${target}` }],
    };
  } catch (error: any) {
    throw new McpError(ErrorCode.InternalError, `Failed to tap: ${error.message}`);
  }
}

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.0.0Mar 18, 2026

TDQS

B3.1/5.0

Behavior2/5

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

With no annotations provided, the description carries full burden for behavioral disclosure. It mentions the action ('Tap') but doesn't clarify what happens after tapping (e.g., UI response, error handling), whether it requires a booted simulator, or any side effects like app state changes. This leaves significant gaps for a tool that interacts with a simulator.

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 directly states the tool's purpose without unnecessary words. It's appropriately sized and front-loaded, with every part contributing essential 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?

Given the tool's moderate complexity (simulator interaction), lack of annotations, and no output schema, the description is minimally adequate but incomplete. It covers the basic action but misses behavioral details like error conditions or simulator state requirements, which are important for effective 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%, so the schema already documents all parameters (x, y coordinates and optional udid). The description adds no additional meaning beyond implying coordinate-based tapping, which aligns with the schema. Baseline 3 is appropriate when the schema does the heavy lifting.

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 ('Tap') and target ('at specific (x, y) coordinates on the simulator screen'), providing a specific verb+resource combination. However, it doesn't explicitly distinguish from sibling tools like 'tap_id', 'tap_relative', or 'tap_text', which offer alternative tapping methods.

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?

No guidance is provided on when to use this tool versus alternatives like 'tap_id' (tapping by element ID), 'tap_relative' (tapping relative to screen dimensions), or 'tap_text' (tapping by text content). The description only states what the tool does, not when it's appropriate.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

Deploy Server

tap