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

Annotations already declare readOnlyHint=true and openWorldHint=true, so safety is covered. The description adds value beyond that by naming the endpoint and disclosing the returned fields (domain, label, tagConfigured), which matters since there is no output schema. It stops short of explaining what tagConfigured means or whether the list is ordered.

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 sentences, zero filler: the first establishes the operation and endpoint, the second front-loads the actionable instruction with examples. Every clause 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?

With no output schema, the description usefully enumerates the return fields, which is the main risk area for a zero-param list tool. Minor gap: 'tagConfigured' is unexplained and there is no hint about result count or ordering.

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 the baseline is 4. The description goes slightly beyond by explaining the shape of the marketplace value the agent will later pass to other tools (domain strings like amazon.com / amazon.se), which aids correct downstream invocation.

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 ('List supported Amazon storefronts') plus the backing endpoint GET /api/v1/marketplaces. No sibling tool in the list does marketplace enumeration, so the agent can distinguish it immediately.

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 to 'Pick the user's store and pass it as marketplace', which explains the downstream purpose of the call and gives concrete examples (amazon.com for US, amazon.se for Sweden). It doesn't name which sibling tools consume the value, but there is no competing alternative to disambiguate against.

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