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

With readOnlyHint and openWorldHint already declared, the description adds real context beyond annotations: tagConfigured is false until real Associates IDs exist, and the concrete consequence that buyUrl omits ?tag=. It does not state whether the list is static or the domain format expected, but the notable data-state caveat is disclosed.

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 dense sentences with the field list and the mandatory downstream behavior front-loaded; nothing is wasted. Minor cost: identifiers like currencyHint are packed into the parenthetical without explanation, slightly straining readability.

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 zero-parameter, zero-annotation-burden listing tool with no output schema, the description covers what it returns, why it matters, and the one surprising field value. An agent can call it and act on the result without further inference.

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?

The tool takes zero parameters, so there is nothing for the description to disambiguate and the baseline is 4. The parenthetical field list describes return values rather than inputs, which adds value but does not change the parameter story.

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?

Specific verb + resource ("List supported Amazon storefronts") followed by the exact fields returned in parentheses, so the agent knows both the shape and content of the result. It is clearly distinguishable from siblings like get_catalog or resolve_product, which consume the marketplace value rather than enumerate it.

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?

Explicitly directs the agent: "MUST pick the user's marketplace and pass it on search/catalog/resolve," naming the downstream tools that require the value. This is a clear when-and-how directive rather than implied usage, and there is no competing alternative to exclude.

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