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

Annotations already declare readOnly, idempotent, and non-destructive, so the description doesn't need to argue safety. It adds genuine behavioral value beyond them: that only enabled and paused groups are returned, that the bid is denominated in the marketplace's currency, and that pagination follows the list_campaigns contract.

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 scope and returns before the optional filter and pagination note. Every clause carries information; nothing is repeated from the title.

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 six-parameter, read-only listing tool with no output schema, the description covers scope, return fields, currency semantics, and pagination. It leaves output shape only partially specified (no mention of what a page envelope looks like beyond the list_campaigns analogy), which keeps it just below complete.

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?

Schema coverage is 100%, so every parameter including limit, cursor, states, and ad_products is already documented in the schema. The description reinforces marketplace_id and campaign_id but adds no format or semantics beyond what the schema states, so the baseline of 3 applies.

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 ad groups) plus the scope constraint (one marketplace) and returns (campaign, default bid, currency). It also anchors itself against the pagination convention of the sibling list_campaigns, so an agent can pick it apart from list_ads or list_targets 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?

"Pass `campaign_id` for one campaign's ad groups" gives a concrete conditional for narrowing scope, and the marketplace scoping is stated up front. It stops short of explicit when-not guidance (e.g. how it differs from list_ads when looking for creative-level data), so not a 5.

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