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

Annotations only declare generic safety hints (readOnlyHint=false, destructiveHint=false, openWorldHint=false); the description adds genuinely new behavioral facts: per-property name uniqueness, idempotent semantics, the alreadyExisted: true return, and that there is never anything to retry. That is exactly the mutation-behavior context an agent needs beyond the annotations.

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?

Four tight sentences, front-loaded with the action, then idempotency semantics, then the alternative-tool pointer, then storage/matching behavior. Every sentence earns its place with no 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?

An output schema exists, so return values need not be re-explained, and the description still usefully names alreadyExisted. Combined with annotations and the alternative-tool routing, it is nearly complete; the only gap is that siteUrl semantics and the keyword/name limits are unaddressed.

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; it partially does, mapping name (unique per property), keywords (stored as text, matched against GSC queries), and implying the property via siteUrl. It adds no format or constraint detail (URL shape, max 1000 keywords, max 200 chars) for siteUrl or the limits.

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 (creates), resource (topic cluster), and scope (on a property, grouping keywords under a name), so the agent knows exactly what is produced. It also explicitly names the sibling update_topic_cluster, distinguishing it from the update path.

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 explicit when-to-use routing ("Use update_topic_cluster to change an existing cluster's keywords") and the precise condition under which the call is a no-op (name already exists returns alreadyExisted: true). Nothing about tool selection is left to inference.

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