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

Adds substantial context beyond the annotations: the call returns the new app state with the next snapshotId (no extra snapshot required), stale-window calls are no-ops that return current state for retry, 'a sent action is not proof the task succeeded', and required ui/process permissions. This is rich behavioral disclosure for a non-read-only, non-destructive tool.

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 sentence, and the remaining sentences carry real value (return shape, stale-state handling, verification caveat, permissions). Slightly dense for five sentences, but nothing is padding.

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 usefully explains the return value and error/retry semantics, and covers permissions. Remaining gap is elementId semantics (valid range, how it maps to a snapshot element), which neither the schema nor the description fully supplies.

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 50% (deviceId and workSessionId documented, elementId and snapshotId bare). The description partly compensates by tying elementId to an element 'of the latest app_snapshot' and explaining that the returned snapshotId feeds the next call, but it adds no format or constraint detail for either parameter.

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+resource: step an adjustable element (slider/stepper) down by one step, operating on the latest app_snapshot. The directional 'down' implicitly and cleanly separates it from the app_increment sibling without needing to name it.

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 (must act on the latest app_snapshot, needs ui and process permission) and recovery guidance when the window changed. It does not explicitly say when to prefer this over app_increment or app_select, so it stops just short of full routing guidance.

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