Set the browser viewport width and height in pixels to test page layouts at specific screen sizes.
Set viewport dimensions in pixels.
| Name | Required | Description | Default |
|---|---|---|---|
| width | Yes | Width in pixels | |
| height | Yes | Height in pixels |
Changes observed during successful MCP inspections.
v1.0.0Input schema / properties / height / descriptionPrevious value: -"Viewport height in pixels"New value: +"Height in pixels"Input schema / properties / width / descriptionPrevious value: -"Viewport width in pixels"New value: +"Width in pixels"Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
The annotation readOnlyHint=false already discloses that this is a mutating operation. The description adds no further behavioral context (e.g., side effects on screenshots or layout). It is a simple setter, so the lack of extra detail is acceptable, but no additional value beyond the annotation.
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, efficient sentence that immediately conveys the tool's purpose. No filler or redundant information.
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 setter with two well-described parameters, no output schema, and a mutating annotation, the description is complete. It provides the essential information (action, target, unit) without unnecessary elaboration.
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?
The schema covers 100% of parameters with descriptions ('Width in pixels', 'Height in pixels'), so the description adds no new semantic meaning. The description only states the purpose, and the schema already handles parameter details.
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 'Set viewport dimensions in pixels' uses a specific verb ('Set') and resource ('viewport dimensions'), with units specified. It clearly distinguishes from sibling tools by focusing on viewport sizing, which no other tool addresses.
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 usage is clear: use when needing to adjust viewport size. No explicit exclusions or alternatives are mentioned, but there is no overlapping sibling tool, so the context is sufficient. Minor gap: no mention of whether this affects the current page or future navigations.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.