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

Goes well beyond the annotations: it discloses the non-mutation guarantee ('without changing its text'), the return behavior (new state with next snapshotId, so no extra snapshot needed), the failure mode (window changed => no-op with current state returned for retry), a caveat that a sent action is not proof of success, and the required ui/process permissions. This is exactly the auth, side-effect, and failure-handling context annotations don't carry.

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?

Purpose is front-loaded in the first clause, followed by return behavior, error handling, and permissions in short declarative sentences. The slogan-like line 'A sent action is not proof the task succeeded' is a touch cryptic, but overall there is little waste for the amount of behavior conveyed.

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?

With no output schema, the description still explains the return value (new app state plus the next snapshotId), the error path (window changed, nothing done, state returned to retry from), and the permission prerequisites. Nothing an agent needs before calling this tool is missing.

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 only 50% (deviceId and workSessionId documented, elementId and snapshotId not), so the description has to compensate. It clarifies that elementId should point to a text field and that snapshotId refers to the latest app_snapshot, adding real meaning. It still leaves the elementId numbering scheme and snapshotId sourcing partially implicit, so not a full 5.

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?

States a specific verb and target: 'Put the keyboard focus in a text field of the latest app_snapshot.' This is clearly distinguishable from siblings like app_type (which changes content) and app_press/app_select (which act rather than focus). The scope clause 'without changing its text' pins the intent precisely.

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?

Gives clear operating context: it works on the latest app_snapshot, does nothing if the window changed, and requires ui and process permission. It does not explicitly name which sibling to use when you actually want to type, but 'without changing its text' implies the split with app_type, so guidance is present though not exhaustive.

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