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clivejefferies

mobile-debug-mcp

tap

Dispatches a tap at specified x and y coordinates on a mobile device. Use for direct screen interaction during testing.

Instructions

Purpose: Dispatch a tap at specific screen coordinates.

Inputs:

  • x, y coordinates

  • platform (optional)

  • deviceId (optional)

Output Structure:

  • action_id, timestamp (ISO 8601), action_type

  • lifecycle_state: post-dispatch lifecycle state (pending_verification or failed)

  • source_module: runtime source of the action envelope

  • target.selector = { x, y }

  • success = true when the tap was dispatched

  • failure_code/retryable when dispatch fails

  • ui_fingerprint_before/ui_fingerprint_after when available

Recommended Usage:

  1. Resolve coordinates deterministically

  2. Call tap

  3. If needed, wait for transition using wait_for_*

  4. Verify with expect_screen or expect_element_visible depending on the intended outcome

Verification Guidance:

  • Prefer tap_element over tap when an element can be resolved

  • Follow RESOLVE → ACT → WAIT (if needed) → EXPECT

  • Use expect_screen for navigation and expect_element_visible for local UI changes

  • Do not use wait_for_* alone as final verification when an applicable expect_* tool exists

Failure Handling:

  • TIMEOUT → retry once

  • UNKNOWN → capture a snapshot and stop

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
xYesX coordinate
yYesY coordinate
deviceIdNoDevice Serial/UDID. Defaults to connected/booted device.
platformNoPlatform to tap on
Behavior5/5

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

With no annotations provided, the description carries full burden. It details the output structure (action_id, timestamp, lifecycle_state, success flag, failure codes, UI fingerprints) and failure handling (retries, snapshot capture). This is comprehensive and transparent.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is well-structured with clear sections (Purpose, Inputs, Output, Usage, Failure). While lengthy, each section adds necessary guidance. Minor redundancy could be trimmed but overall efficient.

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

Completeness5/5

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

Given no output schema, the description compensates by detailing the output structure thoroughly. It also covers the recommended workflow, failure handling, and reference to sibling tools (tap_element, wait_for_*, expect_*). Complete for the tool's complexity.

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

Parameters4/5

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

Schema coverage is 100%, so baseline is 3. The description adds context by summarizing parameters (x, y coordinates, optional platform and deviceId) and implying defaults. It does not repeat exact schema details but adds value by grouping optional fields.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool dispatches a tap at specific screen coordinates, distinguishing it from tap_element which should be preferred when an element is available. The verb 'dispatch' and resource 'tap at coordinates' are specific.

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

Usage Guidelines5/5

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

The description includes a Recommended Usage section with a clear sequence (RESOLVE → ACT → WAIT → EXPECT) and explicit guidance to prefer tap_element over tap. It also provides Verification Guidance and Failure Handling, detailing when and how to use the tool.

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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