emulate_custom_device

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

No annotations are provided, so the description carries the full burden. It does not disclose whether this tool overrides existing emulation, how it interacts with 'emulate_clear_all', or whether setting 'mobile' affects touch behavior. For a mutation tool, this lacks essential side-effect context.

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, front-loaded sentence with a parenthetical that efficiently enumerates the metric categories. Every word earns its place with no redundancy.

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?

The tool itself is simple, and the schema fully documents parameters. However, given the lack of annotations and the many sibling emulation tools, missing guidance on when to clear or how custom settings stack with others leaves the agent to infer behavior. It is minimally acceptable but not complete.

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?

With 100% schema description coverage, each parameter (width, height, mobile, deviceScaleFactor) is already well-defined. The description adds only a high-level grouping (viewport size, scale, mobile mode) without new details, matching the baseline of 3.

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 uses a specific verb 'Set' with a clear resource 'custom device metrics' and lists the key dimensions (viewport size, scale, mobile mode), which distinguishes it from sibling tools like 'emulate_device' that likely target predefined devices.

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 word 'custom' implies use when predefined device emulation is insufficient, but there is no explicit guidance on when to use this versus alternatives like 'emulate_device' or how it interacts with other emulate_* tools. No exclusions or alternative naming are provided.

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