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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered; the description earns credit for adding non-obvious behavior — the locale-based default routing and the fact that two storefronts have curated catalogs with /dp links. It stops short of describing the returned record shape (domain, locale, currency), leaving a small gap.

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 sentences, no filler, and the critical default-routing rule comes last where it belongs after the core purpose. Every clause carries distinct 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 no-parameter read-only list tool with annotations covering safety, the description supplies purpose, contents, and default behavior — enough to invoke correctly. The only missing element is what a returned storefront entry contains, which matters slightly more given there is no output schema.

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?

Zero parameters, so the baseline of 4 applies. The description's mention of 'marketplace' refers to arguments of other tools (search/catalog/resolve), not this one, which is still useful connective context but not parameter documentation for this call.

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 plus resource ('List supported Amazon storefronts'), immediately followed by the concrete contents (amazon.com US and amazon.se) and the distinguishing trait of each (hand-picked catalogs with /dp links). No sibling tool lists storefronts, so the agent can select it unambiguously.

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 states the downstream action: pass the marketplace value to search/catalog/resolve when the user's store is known. It also documents the fallback behavior (en-US defaults to amazon.com, everything else to amazon.se), which tells the agent exactly what happens if it skips this tool.

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