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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds useful context that the result should be used to pick a marketplace for downstream tools, but it does not describe the return format (e.g., whether IDs or names are returned) or any other behavioral traits beyond what annotations provide.

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 concise sentences with zero waste. The core purpose is front-loaded, and the mandatory usage guidance follows immediately. Every sentence earns its place.

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 simple zero-parameter list tool with no output schema, the description provides enough context: it tells what is listed and how to use the result. It could be slightly more complete by specifying what the list contains (e.g., marketplace IDs vs. names), but nothing essential for calling it correctly is missing.

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 to document in the schema. The description correctly focuses on how the output should be used rather than parameter semantics. Baseline 4 applies for a 0-param tool.

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 ('List') and resource ('supported Amazon storefronts'), making the tool's function immediately clear. It does not explicitly name sibling tools it differs from, but the domain is distinct enough that an agent can distinguish it from wishlist/catalog tools without opening schemas.

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?

Provides clear usage context: 'Agents MUST pick the user's marketplace and pass it on search/catalog/resolve.' This tells the agent when to use this tool and what to do with its output. It lacks explicit when-not-to-use or exclusion criteria, but the directive is strong enough for correct invocation.

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