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

Annotations already declare readOnlyHint=true, idempotentHint=true and destructiveHint=false, so the safety profile is covered. The description usefully adds cardinality (one record per advertiser+country) and the full field set, but says nothing about pagination, empty-account behavior, or ordering — extra context beyond annotations, but shallow on operational traits.

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, both front-loaded: what is returned first, then how to use the result. The field enumeration is dense but purposeful, and no sentence is filler.

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 carries the burden of describing the return shape and does so explicitly (id, country, currency, time zone, advertiser name/type, structure counts). For a zero-parameter read tool, nothing an agent needs before calling 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 the baseline is 4 and the schema has nothing to document. The description compensates by explaining the semantic meaning of the one output identifier (`id`) and where it must be passed, which is the only parameter-like concept here.

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 the connected Amazon Ads marketplaces') and immediately scopes the grain: 'one per advertiser and country'. It also enumerates the returned fields, so an agent knows exactly what it gets without opening a schema.

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?

Gives clear downstream chaining guidance: the returned `id` is the `marketplace_id` for list_campaigns, list_ad_groups, list_targets, list_ads and get_streaming_tv_report, which makes it an obvious entry point. It does not state exclusions or contrast with siblings like get_account, but for a root listing tool there is little ambiguity to resolve.

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