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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety burden is covered. The description adds two useful behavioral facts not in the annotations: it does not call the Meta API and it is free, which is exactly what an agent needs before a discovery call.

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 tight sentences, front-loaded with the core action and followed by the return contract and the cost caveat. Dense but every clause carries information; 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?

With no output schema, the description correctly enumerates the returned fields (tool_name, router with null meaning, title, summary, read_only, spend), which is the main completeness gap this tool would otherwise have. It is close to fully sufficient, missing only details like ranking order or what happens when top_k is omitted beyond the schema's stated default.

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 the baseline is 3. The description goes further by explaining how 'query' is actually consumed — words are matched against operation names, titles and descriptions and used to rank results — which is semantic information the schema's example does not convey. Only top_k behavior is left entirely to the schema.

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: it ranks the server's Meta operations against query words and returns a defined set of fields. It is clearly distinguishable from siblings like get_tool_schema and start_here, though the 'Meta operations' scope could be read as excluding the non-Meta siblings (google_ads_*, audit_*, etc.).

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 implied rather than stated: an agent can infer this is a cheap discovery step ('Free', 'Does not call Meta'), but there is no explicit when-to-use guidance or routing against alternatives such as get_tool_schema or start_here.

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