List voices

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

The description is consistent with the readOnlyHint annotation and adds context: it lists both stock and custom voices, and explains the output is voice IDs for create_video. It also discloses the snapshot nature, going beyond annotations.

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?

The description is three sentences, front-loading the main purpose. Every sentence adds value: purpose, output usage, and an important note. No unnecessary words.

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?

Given the low complexity (3 optional parameters, no required), the description fully covers what the tool does, what it returns, and caveats. The lack of output schema is compensated by describing the return value's purpose.

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% and all parameters have descriptions. The tool description does not add new information about individual parameters beyond the schema, so the baseline score of 3 is appropriate.

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?

The description states explicitly 'List Synthesia text-to-speech voices', specifying the verb and resource. It distinguishes from sibling tools like list_avatars by focusing on voices, and clarifies the two types of voices (stock and custom).

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 description provides clear guidance: voices are optional and if omitted, the system uses a recommended voice. It also warns that the stock list is a snapshot and may be incomplete, setting proper expectations.

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