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

With no annotations, the description carries the behavioral disclosure burden. It clearly states this only changes the window and is not a real hardware device, which is the key non-obvious behavior. It does not mention return values or side effects, but for a simple viewport resize, the main behavioral caveat is covered.

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 front-loaded with the core action and includes useful caveats about real-device fidelity and alternative device selection. It is slightly repetitive with the 'real handset' warning appearing twice, but every sentence still contributes meaningful guidance.

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 three-parameter resize tool with no output schema, the description covers purpose, usage context, limitations, and the alternative path. The schema handles parameter details, and the description fills in the behavioral context needed for correct 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?

The input schema already documents all three parameters with 100% coverage, so the baseline is 3. The description adds no additional parameter-level meaning beyond referring to pageId and viewport/window terminology already present in the schema.

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 names a specific verb and resource: 'Resize the DESKTOP grid browser viewport (by pageId)' and immediately distinguishes the tool from real-device resizing. It is clear this is a viewport-level operation, not a device emulator.

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?

It explicitly tells the agent when to use it ('checking responsive breakpoints without a real handset') and when not to ('A real phone is still the honest test'). It also directs the agent to pick a different device by udid for actual device behavior, providing a concrete alternative.

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