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

Annotations already signal readOnly, idempotent, and non-destructive behavior, so the bar is lower. The description adds useful behavioral context beyond that: it uses current 2026 price bands, accounts for delivery cost, VAT/GST, and KDP Select rules, and is a pure calculation tool with no contradiction against the annotations.

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?

Three dense sentences front-load the main action and then neatly separate eBook, paperback, and KU cases. There is no filler, no repetition of schema enums, and every clause contributes useful information.

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 tool with 11 parameters and no output schema, the description covers the core royalty paths well but leaves gaps: monthlySales is never explained, paperback printing-cost inputs (ink, trim, pages) are only implied, and the expected return/breakdown shape is not described. An agent could call it correctly after inference but not fully from explicit guidance.

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 only 45% schema description coverage, the description compensates by connecting inputs to calculation logic: fileSizeMb drives delivery cost, kdpSelect and marketplace govern the 70/35 option and store list, and kuPagesReadPerMonth feeds KU earnings. It leaves monthlySales and the ink/trim cost relationship implicit, so it does not earn 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?

The description uses a specific verb ('Calculates') and a precise resource ('KDP royalties per sale'), then expands with eBook vs paperback, store coverage, and KU earnings. This makes it immediately distinguishable from sibling tools like keyword_research and bsr_to_sales, none of which perform royalty math.

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 first sentence makes the core use case explicit: call this whenever a KDP royalty or Kindle Unlimited earnings figure is needed. It does not list exclusion conditions or name alternatives, but the sibling tools are clearly separate functions, so the context is unambiguous.

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