get_invoices

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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the description's added value is the variable-result behavior: the HTML summary is always present, PDFs are optional and seller/site dependent. That is genuinely useful expectation-setting. It does not cover empty results, invalid order IDs, or any auth requirement, so it stops short of full disclosure.

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?

A single front-loaded sentence that names the resource first and then enumerates the returned document types. Every clause earns its place; nothing is padded.

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 an output schema present, return values need not be explained, yet the description still frames their variability well. The only gap is behavior on failure or empty-invoice cases, which an agent would have to discover at call time.

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%, and the site parameter already explains the default-site behavior and the check_session reference. The description only restates that an Order ID is required, adding no format or usage nuance beyond the schema, so the baseline of 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 ('Get the invoice documents') scoped to an Amazon Order ID, and enumerates the artifacts returned: Printable Order Summary HTML plus seller-issued invoice and credit-note PDFs. This clearly separates it from order-detail siblings like get_order or get_orders without needing to name them.

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 resource itself (ask for invoices of an order), and 'mostly on EU sites' implicitly warns that PDFs may not exist on all marketplaces. But there is no explicit when-to-use vs get_order, no statement that the order must already exist, and no note about needing a session (that hint lives only in the site parameter's schema text).

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