tap

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

With no annotations provided, the description carries the full transparency burden. It discloses that the touch is 'real' (not synthetic) and that coordinates are in CSS pixels relative to the viewport. However, it does not mention potential side effects, failure modes (e.g., out-of-bounds coordinates), or whether the touch triggers standard events, leaving some behavioral ambiguity.

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 exceptionally concise: two sentences, front-loaded with the primary action and followed by a single usage guideline. Every word serves a purpose, with no redundant information or repetition of schema details.

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?

For a simple two-parameter tool with no output schema or annotations, the description covers the essential context: what the tool does, the coordinate system, and when to use it. It omits nothing critical for an AI agent to select and invoke the tool correctly, though a note on coordinate bounds or error handling would make it fully complete.

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?

The input schema lists only x and y as required integers with no descriptions (0% schema coverage). The description compensates by specifying 'viewport coordinates (CSS pixels)', which clarifies the coordinate system and units for both parameters. This adds meaning beyond the bare schema, though it could define the origin (e.g., top-left) more explicitly.

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 function: 'Send a real single-finger touch at viewport coordinates (CSS pixels).' It uses a specific verb ('send') and resource ('touch at viewport coordinates'), which distinguishes it from sibling tools like 'click' that rely on selectors.

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 second sentence explicitly advises when to use the tool: 'Use when there is no sensible selector — e.g. a canvas or a custom overlay.' This provides a clear usage context and implicitly contrasts with selector-based alternatives like 'click', though it does not name the alternative tool directly.

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