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

Annotations only declare that this is a non-read-only, non-destructive mutation. The description adds two genuinely useful facts beyond them: the name must be unique per library in a case-insensitive comparison (a failure mode the agent must avoid), and the call requires write scope. It does not say what error surfaces on a duplicate name or whether optional fields can be updated later.

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?

Three short sentences, zero filler, with the core action front-loaded and the constraint and auth requirement following in order of importance. Nothing could be removed without losing information.

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 10-parameter creation tool with no output schema and only sparse annotations, the description covers identity and prerequisites but is thin on outcomes: it never says what is returned (e.g. an audience ID usable by attach_audience_to_campaign) or how optional arrays like discovery_keywords affect discovery behavior.

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% across 10 parameters, so the schema already carries the parameter semantics and a baseline 3 applies. The uniqueness constraint on `name` is the only added meaning, and it is not framed at the parameter level or tied to a specific field name.

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 concrete verb+resource: "create a library audience profile", and the adverb "manually" implicitly distinguishes it from generated audiences (the sibling generate_audiences). It stops short of naming that alternative explicitly, so the differentiation requires a small inference.

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?

"manually" hints at when to choose this over a generate-and-pick flow, and "requires write scope" gives a prerequisite. There is no explicit when-not guidance, no mention of what to do with the resulting audience (e.g. attach_audience_to_campaign), and no stated alternative.

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