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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint, so the safety profile is covered. The description adds real behavioral value beyond that: it discloses the returned payload (extensions at campaign and account level plus a `gaps` list of what a search campaign is missing), which is the only source for return shape given there is no output schema.

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?

A single, front-loaded sentence enumerating resource types before scope, with no filler. It is slightly run-on and packs the return payload description into the same sentence, but 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?

For a two-parameter read tool with strong annotations and no output schema, the description adequately covers what is returned (including the gaps list). However it omits the required customer_id parameter and offers no usage routing, so it is not fully complete for correct invocation.

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 description coverage is 0%, so the description must carry parameter meaning, and it largely does not. It implies campaign_id is optional and scopes the query, but customer_id — the only required parameter — is never mentioned or explained, leaving an agent to guess its role and format.

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 names the specific resource (sitelinks, callouts, structured snippets, call assets) and its scope (campaign level, optionally one campaign, and account level), so an agent knows exactly what data comes back. The verb 'list' is carried by the name rather than stated, and there is no explicit differentiation from the ads_add_extensions / ads_remove_extension siblings, so it falls short of a 5.

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?

Usage is only implied: the parenthetical '(optionally one campaign)' hints that supplying campaign_id narrows the result, but there is no explicit when-to-use, when-not, or named alternative. The agent can infer this is the read path versus ads_add_extensions / ads_remove_extension from the name, but the description does no routing work itself.

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