spine_width

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

With no annotations, the description must carry the burden, and it does disclose the output unit (inches), which is genuinely useful behavioral context. It does not say whether the result is rounded, which paper-stock formula or KDP revision it follows, or that it is a pure calculation with no side effects.

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?

One sentence, front-loaded with the verb and the output unit, with no filler. It is efficient, though it is so terse that the unit and the enum values are the only extra facts conveyed.

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 two-parameter pure calculation with no output schema, the description covers input meaning and output units adequately. It leaves out any input constraints and the exact form of the return value, which the missing output schema means the description should have supplied.

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 description coverage is 0%, so the description must compensate, and it does: it maps 'pages' to page count and 'paper' to paper type while supplying the two enum values (white or cream) that the raw schema lacks. It omits KDP page-count bounds and whether even page counts are required, which keeps it from a 5.

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?

It names a specific verb and resource: 'Compute KDP paperback spine width in inches', which is unmistakable and cannot be confused with list_trim_sizes or build_book. It stops short of explicitly distinguishing itself from those siblings, so it lands at 4 rather than 5.

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?

By saying the tool works for a page count and paper type in a KDP paperback context, it implies when the tool applies. It gives no explicit when/when-not statements and does not name build_book as the alternative for full book assembly, so the guidance is only implied.

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