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

Annotations already declare readOnly, idempotent and non-destructive, so the safety profile is covered. The description adds genuinely non-annotation context — 'No account needed' (auth requirements) and the consent caveat for using a person's own photo — which is exactly the kind of behavioral detail the schema cannot express. No pagination or catalogue-size behavior is mentioned, so not a full 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?

A single front-loaded sentence that states what the agent gets before the secondary consent note. Efficient with no filler, though the trailing photo/consent clause is slightly tangential to 'list the catalogue'.

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?

An output schema exists, so return values need no further explanation, and the description still volunteers the key fields. Combined with annotations covering safety and a no-parameter schema, the definition is complete enough for correct invocation; only routing alternatives are thin.

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?

The tool takes zero parameters, so per the baseline there is nothing for the description to document. The field mentions (name, style, portrait URL) describe output, not inputs, but do no harm.

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 (see/list) and resource (catalogue of UGC creators) and enumerates the returned fields (name, style, portrait URL). It also ties itself to the consumer tool generate_ugc_video, which helps separate it from list_models and list_generations. 'See' is a slightly soft verb, keeping it just below a 5.

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?

Implies usage by naming generate_ugc_video and its accepted fields, so the agent can infer this is the pre-flight lookup for that tool. However, it never states when-not to use it or names alternatives like list_models or generate_avatar explicitly, leaving routing somewhat inferred.

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