vphone-mcp

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

No annotations are provided, so the description carries full burden. It mentions coordinate system details and default duration, but doesn't disclose critical behavioral traits: whether this requires specific permissions, if it's destructive (could trigger unintended actions), what happens on invalid coordinates, or what the output schema contains. For a UI interaction tool with zero annotation coverage, this leaves significant gaps.

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

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

The description is perfectly structured and concise. The first sentence states the core purpose, the second provides essential coordinate context, and the Args section efficiently documents all parameters with clear explanations. Every sentence earns its place with zero wasted words.

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

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

Given 5 parameters with 0% schema coverage and no annotations, the description does well on parameter documentation but lacks behavioral context. The presence of an output schema means return values don't need explanation, but for a UI interaction tool that could have side effects, more guidance about permissions, error conditions, or relationship to siblings would improve completeness.

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

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

Schema description coverage is 0%, so the description must fully compensate. It successfully does this by clearly explaining all 5 parameters: defining x1/y1 as start coordinates, x2/y2 as end coordinates, and duration_ms with its default value. The coordinate system context (pixels matching screenshot dimensions) adds crucial meaning beyond the bare schema types.

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

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

The description clearly states the tool's purpose: 'Swipe from one point to another' which is a specific verb (swipe) with clear action. It distinguishes from siblings like tap, scroll, or swipe_to_next_page by specifying coordinate-based movement rather than named actions. However, it doesn't explicitly contrast with swipe_to_next_page/swipe_to_previous_page which might be specialized versions.

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

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

The description provides some context about coordinate systems and screenshot dimensions, which implies usage when precise screen coordinates are known. However, it doesn't explicitly state when to use this vs. siblings like swipe_to_next_page or scroll_up/down, nor does it mention prerequisites or alternative scenarios. The guidance is implied rather than explicit.

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