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

Annotations already declare a safe, idempotent, non-destructive read. The description adds real value beyond them by disclosing what comes back (custom voices plus the remaining custom-voice quota) and how the returned identifier should be consumed. Pagination or result-size behavior is not mentioned, keeping it at 4.

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 filler, front-loading what the tool lists and then how to use the output. Every clause earns its place with no redundancy.

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 input parameters and no output schema, the description carries the burden of describing the return payload, and it does: custom voices plus remaining quota, plus the key field name (`voice`). Nothing an agent needs to call and consume this correctly is missing.

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 the schema has nothing to document and there is no parameter semantics to add. Baseline 4 applies; nothing in the description is needed here.

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 (List) and resource (the user's personal custom voices), and narrows the scope by naming the two creation paths (Voice Design, Voice Clone). This distinguishes it clearly from siblings like list_voices and list_favorite_voices without opening their schemas.

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?

Gives concrete downstream guidance: 'Use `voice` from the result in any speech tool,' which tells the agent why and when to call this. It does not explicitly name the alternative tools (list_voices, list_favorite_voices) or state when not to use it, so it stops short of full routing guidance.

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