Emulate Mobile Device

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

Annotations indicate not read-only, but description adds that session state (cookies/login) carries over and that the page is re-opened. This provides useful behavioral context beyond the basic annotation flags.

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?

Every sentence earns its place: first sentence states core purpose, second explains distinction from resize, third covers state carry-over, fourth gives examples, fifth suggests observation. No redundancy, well-structured.

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?

Given the tool's simplicity (1 param, output schema present, annotations provided), the description covers purpose, usage context, behavioral effects, and follow-up actions. It is complete for an agent to correctly select and invoke the tool.

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?

Input schema has a single string parameter with 0% description coverage. The description provides example device names and explains the parameter's role, adding meaning beyond the schema. However, no formal restrictions or enum values are given.

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 re-opens the page as a mobile device with full device identity (touch, UA, DPR, viewport), distinguishing it from resize() which only changes dimensions. It lists common device names, making the purpose specific.

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?

Explicitly contrasts with resize() for plain breakpoints vs true device emulation, recommends using observe() after, and mentions session state carry-over. Provides clear when-to-use and when-not-to-use guidance.

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