Tap

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

The annotation readOnlyHint=true directly contradicts the description's 'Tap the screen,' which is a physical mutation/injection action, not a read-only operation. This is a serious annotation contradiction and violates transparency expectations. No other behavioral details are disclosed beyond what annotations already state.

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?

Two sentences, front-loaded with the primary action, and every sentence adds practical guidance. No filler or redundancy.

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 tap tool with 5 parameters, the description covers the essential coordination strategy and parameter selection. It does not explain return values (no output schema exists) or the device serial default, but these are adequately left to the schema. The annotation contradiction is noted but does not impact the completeness of the textual description.

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 coverage is 100%, providing baseline parameter descriptions. The description adds valuable guidance on the relationship between pixel and percentage parameters, explaining when to prefer snapshot_ui coordinates versus estimating percentages from screenshots, which goes beyond the schema.

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 taps the screen, using a specific action (tap) on a specific resource (screen). It also distinguishes itself from siblings like tap_element by mentioning coordinate-based input from snapshot_ui and pixel/percentage alternatives, making it unambiguous.

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?

Provides clear context on how to obtain coordinates (prefer snapshot_ui pixels) and when to use percentages (safer when estimating from screenshots). It does not explicitly contrast with alternatives like tap_element, but the guidance is directly useful for selecting the right parameter approach.

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