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

Annotations already cover readOnly/destructive/openWorld, but the description adds genuinely useful context by pre-empting the surprise that a 'POST /products/spine' call has no side effects ('nothing is created or charged'). It doesn't cover error behavior for invalid SKUs, but for a pure calculation the safety profile is fully addressed.

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 short sentences with the unit (mm) and purpose front-loaded, followed by the no-side-effects reassurance. The endpoint path is mildly redundant but is what makes the 'pure calculation' claim concrete.

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 4-parameter calculation tool with no output schema, the description supplies the return unit (mm) and the value returned (spine width), which is the key missing piece. Only edge-case behavior (invalid SKU, out-of-range page counts) is left unaddressed.

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 100%, so each parameter is already documented; the description only reinforces the relationship between number_of_pages and the returned width. It says nothing extra about sku, destination_country_code, or state, so the baseline 3 applies.

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?

States a specific verb and resource ('Calculate the spine width in mm of a book product') plus the input that drives it (page count) and the use case (cover artwork). An agent can distinguish this from prodigi_create_quote or prodigi_get_product without opening any schema.

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?

'for a page count (for cover artwork)' gives clear context for when to reach for this tool, and 'nothing is created or charged' implicitly routes the agent away from quote/order tools for what is a look-up. No explicit named alternative or exclusion, so it stops short of 5.

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