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

Annotations already declare readOnlyHint, destructiveHint=false, and openWorldHint=false, but the description adds real context beyond them: 'No writes or access grants' reaffirms the read-only surface, and the statement that restricted services require fresh server-verified access and otherwise refuse discloses an auth/refusal behavior. The auth detail is somewhat vague ('restricted services', 'fresh server-verified'), keeping it short of a 5.

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 with the read action front-loaded and no filler. The phrase 'bounded native reach_products insight' is slightly cryptic jargon, but nothing is wasted.

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, a read-only 3-param tool with nested input and 33% schema coverage needs more than this. The description covers the read/refusal profile adequately but leaves parameter semantics and what 'reach_products' returns 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 coverage is only 33%: customer_id carries a description in the schema, but body and connection_context (including the nested required location_id) are undocumented. The description adds nothing about any parameter, so it fails to compensate for the low coverage, especially around the nested body object.

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 (read) and resource (native reach_products insight) with a scoping qualifier ('bounded'). It is clear what the tool does, but it never distinguishes itself from adjacent siblings such as google_ads_reach_forecast or google_ads_reach_locations, so an agent must still infer which reach tool to pick.

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?

There is no when-to-use statement and no routing to alternatives, despite several reach/forecast siblings existing. 'Restricted services require fresh server-verified access and otherwise refuse' is a precondition, not usage guidance about when this tool should be chosen over another.

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