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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so the safety profile is covered externally. The description adds a modest amount by stating that returned entries carry type, size and status, giving a partial picture of what the response contains. It says nothing about result volume, pagination, or whether empty/zero-size audiences are included, so the added behavioral context is thin.

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 short sentence with no filler, leading with the resource. It is efficient and front-loaded, though the absence of a verb makes it slightly less immediately actionable than a 'list X' phrasing would be.

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 zero-required-parameter read tool with full schema coverage and no output schema, the description should at minimum describe the shape of what comes back; it mentions type/size/status but not the record structure, counts, or whether custom and lookalike audiences are returned together. Adequate to call correctly, but not complete for interpreting results.

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% and every parameter (detail, folder, account, language) is fully documented in the schema, including enum meanings. The description adds no parameter meaning beyond that, which is acceptable at the baseline of 3 when the schema does the heavy lifting.

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 resource (custom and lookalike audiences in the account) and the fields surfaced (type, size, status), which tells an agent this is a retrieval tool. But it is a verb-less fragment: it never says whether it lists, retrieves, or analyzes audiences, and it gives no differentiation from parallel audience tools such as meta_audiences or snapchat_audiences.

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 guidance at all — nothing about when to prefer this over other audience or reporting tools, no prerequisites about account/folder selection, and no note that this is read-only enumeration rather than audience creation. The only implied usage comes from the readOnlyHint annotation, not from the text.

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