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

Annotations already establish readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds that the result is a designer rule of thumb and that the answer includes a link to sources, which is useful framing about the precision of the output, but it does not describe the shape of the answer beyond that.

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?

Two sentences, front-loaded with the primary output (width) before the secondary one (bottom-edge height). The parenthetical carries the key heuristics compactly and no sentence is wasted.

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?

With only three simple parameters, full schema coverage, and no output schema, the description covers what the tool returns (width and bottom-edge height) and the governing heuristics. It could be slightly more explicit about the output units/format, but nothing essential for a correct call is missing.

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 100%, so the baseline would be 3, but the description goes further by explaining the relationship between inputs: the mirror is 70-90% of vanity width and one mirror per sink on a double vanity. It implicitly links counter height to the bottom-edge calculation, adding real meaning beyond the field descriptions.

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 concrete, specific language: it computes mirror width from vanity width (70-90%) and the height of the mirror's bottom edge. The resource is clearly distinct from siblings like bar_stool_height or rug_size, though it never explicitly names those alternatives.

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?

Usage is implied by the rules given (bathroom mirrors over a vanity, one per sink for a double vanity), which tells the agent the domain of applicability. However, there is no explicit when-to-use/when-not guidance and no mention of prerequisites or limits such as what happens for vanities outside normal sizes.

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