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

Annotations already establish the safe read-only, idempotent profile, so the bar is lower; the description adds the non-obvious return behavior that results come back 'in their saved order'. It doesn't cover empty-list or error behavior, but for a trivial read that is minor.

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, no waste, with the purpose front-loaded and the usage rule following. Every sentence 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 no-parameter read tool with no output schema, the definition gives enough to call it correctly and know what to expect (favorites in saved order). Only the shape of the returned list itself is left unspecified, which is acceptable given there is no 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?

Zero parameters, so the baseline is 4. There are no argument semantics for the description to add, and nothing is misleading.

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 (voices the user marked as favorites), and adds the scope 'in their saved order', distinguishing it from generic sibling list_voices and list_my_custom_voices. An agent can tell what it returns without opening a 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?

'Check this first when the user did not name a voice' is an explicit routing rule that tells the agent when to prefer this tool. It falls short of naming the alternative (e.g. list_voices) to use otherwise, but the selection condition is clearly stated.

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