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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=true. The description adds genuinely useful behavior beyond that: the catalog is a fixed set of 30 entries and each entry carries name, id, style and preview audio URLs. It does not discuss pagination or caching, but for a static zero-param list this is reasonable coverage.

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 compact sentences with the payload contents front-loaded and the endpoint appended as a trailing anchor. Nothing is padded, though the bare 'GET /voices' adds little for an agent that already has the tool name and schema.

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-parameter, read-only listing tool with no output schema, the description covers what the agent needs: what the collection is, how big it is, and what fields come back. No prerequisites or follow-up routing are described, which keeps it just short of fully complete.

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 no parameters at all (schema is an empty object), so there is nothing for the description to disambiguate. Baseline 4 applies; the field list it gives is about the response, not inputs, and output schema is absent so that detail is a net gain.

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?

Identifies the resource precisely (the fixed catalog of Gemini voices) and enumerates the returned fields, so an agent can distinguish it from vids_list_avatars or vids_list_accounts without opening the schema. It is a noun-phrase description rather than an explicit verb, but the naming and content leave no ambiguity about what the call returns.

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?

The phrase 'an avatar can speak with' implies this is the lookup step before creating or configuring an avatar, which is meaningful context. However, it never states when to call this versus other listing tools or as a prerequisite to vids_create_avatar, so usage is inferred rather than stated.

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