List avatars

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

Discloses that stock list is a snapshot and may be incomplete, and custom IDs must be registered in config, adding value beyond readOnlyHint annotation.

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?

Front-loaded purpose and usage, but includes necessary context; slightly lengthy but not wasteful.

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?

Complete for a list tool: explains return values (avatar IDs), usage in create_video, and limitations of stock and custom sources, compensating for lack of output schema.

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 provides full parameter descriptions (100% coverage), but description adds context for obtaining custom avatar IDs, which enhances understanding.

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?

Clearly states it lists Synthesia avatars (stock and custom) for video creation, distinguishing from sibling tools like list_voices or list_templates.

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?

Explicitly explains when to use (before creating video), notes limitations (stock snapshot incomplete, custom IDs from STUDIO), and directs to use IDs in create_video.

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