Get viewport size

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

With no annotations provided, the description carries the burden of behavioral disclosure. It states the output is in CSS pixels, which is useful, but it does not disclose whether the viewport size is for the current page or the session's default viewport, nor does it mention any side effects or limitations. The description is accurate but minimal.

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 a single, clear sentence that is appropriately sized and front-loaded with the key information. Every word earns its place, and there is no redundancy or unnecessary detail.

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 read-only tool with one parameter and no output schema, the description is nearly complete. It states the return value and unit, which is sufficient for an agent to call it correctly. It could optionally mention that the viewport size is for the current page, but this is a minor gap.

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 the schema already documents the sessionId parameter fully. The description adds no additional parameter semantics beyond what the schema provides, so the baseline of 3 is appropriate.

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 returns the session page's viewport size in CSS pixels, with a specific verb ('Returns') and resource ('session page's viewport size'). It is distinct from siblings like get_scroll_position and get_page_snapshot, so an agent can understand its purpose without confusion.

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?

The description implies usage when an agent needs viewport dimensions, but it does not explicitly state when to use this tool versus alternatives like get_scroll_position or get_page_snapshot. There is no mention of when not to use it or any prerequisites beyond the sessionId parameter.

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