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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false, and openWorldHint, so the agent knows this is a safe, repeatable read. The description adds that the returned items are 'stock presenter avatars' whose ids are consumed downstream, but it does not describe return shape, pagination, or provider-specific behavior. Useful added context, but not rich behavioral disclosure.

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 tight sentences with zero filler; the purpose is front-loaded and the follow-on action comes second. Every clause earns its place.

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 simple, fully-annotated list tool with no output schema, the definition covers what it returns (presenter avatars) and how to use the result. Minor gaps remain around the concrete return structure, but nothing critical for correct invocation 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?

Schema coverage is 100% for the single 'provider' parameter, whose enum-like note ('default heygen, currently the only one') is already in the schema. The description adds nothing about parameters, so the baseline 3 for schema-covered params applies.

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 and resource ('List the stock presenter avatars') scoped to 'AI video generation', and implicitly distinguishes itself from generate_video by being the catalog that feeds it. An agent can tell this is a read-only catalog lookup rather than a generation call without inspecting the schema.

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 clear context for use ('available for AI video generation') and an explicit next step ('Pass an avatar's id to generate_video'), which routes the agent into the follow-on workflow. It stops short of naming the close alternative list_video_voices or stating when not to use this tool.

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