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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so safety is covered. The description adds the substantive context the annotations lack: that this is a name-scoped lookup returning configurations, targeting, size and performance data. No pagination or result-shape detail beyond the schema, which keeps it from 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 sentences with no waste; the payload summary leads and the scoping constraint follows immediately. The all-caps 'A NAME IS REQUIRED' is slightly heavy-handed but functionally front-loads the key constraint.

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?

There is no output schema, so the description does the work of telling the agent what comes back (configurations, targeting criteria, size metrics, performance), which is sufficient for a read lookup. Given the rich schema, nothing critical is missing 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 100%, including a very rich sort field spec, so the schema carries the parameter burden and baseline 3 applies. The description reinforces that name is required and is the lookup key, but adds little that the schema's 'Filter by audience name (supports partial matching)' and required list do not already say.

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?

Specific verb+resource ('Custom audience information') with an enumeration of what is returned (configurations, targeting criteria, size metrics, performance). It also scopes the tool as the by-name lookup rather than an account-wide browse, which separates it from list_audiences without naming that sibling outright.

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?

Explicitly states the name is required and frames the tool as the by-name lookup as opposed to the account-wide browse, giving a clear selection rule. It stops short of naming alternatives like list_audiences or get_deep_audience_details, so the routing guidance is implied rather than fully enumerated.

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