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

With no annotations, the description carries the burden of disclosing behavior. It mentions the fallback nature, coordinate source, and session requirement. However, it does not specify failure modes or return behavior, which are not covered elsewhere, though these are less critical for a tap action.

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 concise and well-structured: opening with purpose, then usage guidance, then a key requirement. Every sentence adds essential information, with no filler 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 action tool with no output schema or annotations, the description covers all critical aspects: what it does, when to use it instead of an alternative, how to obtain valid parameters, and a prerequisite (active session). It is complete enough for an agent to select and invoke correctly.

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%, so the baseline is 3. The description adds value by emphasizing that coordinates are in physical screen points and must originate from ios_page_source, reinforcing the warning against using guesses from screenshots. This goes beyond the schema's parameter descriptions.

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: 'Tap at (x,y) on an iOS device screen.' It also identifies itself as the 'FALLBACK' for elements without labels, distinguishing it from ios_tap_by_label. This specific verb+resource+scope makes the purpose unmistakable.

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?

Explicit guidance is provided: 'Prefer ios_tap_by_label ... whenever the target has a name in ios_page_source.' It also warns that coordinates must come from ios_page_source, not screenshots, and that an active automation session is required. This gives clear when-to-use and when-not-to-use instructions.

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