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

With readOnlyHint/destructiveHint already declaring safety, the description adds real mechanism: it reads the template's own Tailwind responsive classes (deterministic at a fixed width) and copy length against design intent, rather than rendering pixels. Stating what it explicitly does not do ('THIS IS NOT A SCREENSHOT') is useful behavioural context. It stops short of describing output shape or any execution caveats.

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 failure-mode list is front-loaded and informative, but the back half drifts into rhetorical justification about renderers that is longer than the task requires, and the capitalized disclaimer sits mid-paragraph rather than leading. Appropriately sized overall, but several sentences do not earn their place.

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 read-only check with no output schema and only two parameters, the description conveys what is inspected and the non-rendering nature well. It omits how findings are returned or scoped (per page vs whole project), leaving the agent without a full picture of the result it will receive.

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 coverage is 50%: pageName is documented in the schema, but projectId carries no description. The description mentions 'slots' and 'a page' only in passing and adds no meaning about the projectId/pageName parameters, so it does not compensate for the documented gap.

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 enumerates concrete failure modes it detects (copy overflow, unfittable columns, oversized fixed widths, non-wrapping text, unreadable colours, unresolved slot tokens) at phone/tablet/desktop widths, so the resource and scope are clear. It also explicitly distinguishes itself from a screenshot/render check. It never states the verb+'resource' crisply up front, relying on the reader to infer that this is a read-only responsive audit.

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 contrasts itself with the 'second renderer' approach and disclaims being a screenshot, which implies when it is preferred over visual capture. However it never gives a use-this-when instruction, and it fails to differentiate from the very similar sibling uichemy_check_layouts, which an agent would need to choose between.

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