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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered; the description adds real value beyond that by disclosing the shape of the result and the data-quality caveat that tagConfigured may be false until real Associates IDs are configured. This 'honest search-mode' warning prevents the agent from misreading a false flag as an error.

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 short sentences, front-loaded with what is returned before the usage note and the caveat. The phrase 'Honest search-mode' is slightly jargon-ish, but it is immediately explained by the clause that follows, so nothing is wasted.

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 input parameters and no output schema, the description carries the full burden of explaining the return values — and it does, listing the four keys and the meaning of the ambiguous one. An agent has everything it needs to call this and interpret the result correctly.

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 there is no parameter semantics to explain and the baseline is 4. The description instead documents the returned keys, which is the more useful information for a no-arg discovery tool with no output schema.

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') and enumerates the returned fields (id, domain, defaultLocale, tagConfigured), so the agent knows exactly what comes back. It also positions itself relative to the sibling shopping tools by telling the agent to pass the marketplace + locale values onward, which distinguishes it from search/resolve_product/add_item.

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?

The line 'Pass marketplace + locale on shopping tools' makes the tool's role in a wider workflow clear — call this to discover valid identifiers before invoking the shopping tools. It doesn't explicitly state when not to call it or name a specific alternative, but for a zero-arg discovery tool the implied usage is strong.

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