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

Annotations already declare the mutation/idempotency profile (readOnlyHint=false, idempotentHint=false, destructiveHint=false, openWorldHint=true). The description adds real targeting behavior beyond that: it acts on the element matching the selector when present, otherwise on the currently focused element. It doesn't elaborate on failure modes (e.g., no focused target), so it stops short of a 5.

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?

Three tight clauses with no filler; the scope ('DESKTOP grid browser') is front-loaded, followed by key examples, targeting behavior, and the sibling exclusion. Every sentence earns its place.

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 3-param action with no output schema, the description covers scope, input form, targeting semantics, and the sibling alternative — enough to invoke correctly. Minor gap: no mention of what happens if no target is focused, but that is not essential to selection.

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 100%, so pageId, key, and selector are already documented. The description restates the selector behavior ('targets an element when a selector is given, otherwise the focused one') and repeats key examples from the schema, adding marginal value over structured data. Baseline 3 applies.

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?

Specific verb+resource: 'Press a key in the DESKTOP grid browser (by pageId)' with concrete key examples and a chord syntax sample. It explicitly distinguishes itself from the sibling webpage_press_key, so the agent can route without opening either schema.

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?

States both the when ('DESKTOP grid browser') and the when-not with a named alternative: 'Not a device — for a phone or tablet use webpage_press_key.' That is an explicit exclusion plus the routing condition, leaving nothing to inference.

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