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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is clear. The description adds useful context beyond annotations: the result is a list of advertising categories with illustrative examples, and it frames this as a value-discovery operation rather than a standalone data endpoint. For a simple 0-param list operation, this is sufficient added context.

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?

The description is two sentences with no filler. The core behavior is front-loaded, the examples clarify the domain, and the usage guidance is stated explicitly. 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 0-parameter, read-only category-list tool, the description is complete. It covers purpose, the nature of the return value, and the downstream consumer (getMarketplaceAdverts). No output schema exists, but the description's examples and framing give an agent enough to invoke 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?

The tool has zero parameters, and schema coverage is 100% (the schema has no properties). With no parameters to document, the description does not need to explain input semantics. The baseline of 4 applies because the description correctly omits irrelevant parameter detail.

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?

The description states a specific verb and resource: 'Returns the list of Nomad Marketplace advertising categories.' It provides concrete examples ('eSIM', 'Travel Insurance') and explicitly distinguishes its output (categories) from the sibling getMarketplaceAdverts (adverts). An agent can immediately understand what this tool returns and how it relates to nearby tools.

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 description explicitly instructs: 'Use this to discover valid category values for getMarketplaceAdverts.' This names the specific downstream tool and the condition that warrants this call. There is no ambiguity about when to invoke this tool.

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