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

Annotations already declare the operation safe, read-only, idempotent and non-destructive, so the safety profile is covered. The description adds genuinely new context beyond annotations: the pricing model (60 credits up to 60s, then 1 credit/second), which is useful behavioral detail for planning a generation.

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 that front-load the action and return content, then add the pricing rule. Efficient overall, though the credit-cost sentence arguably belongs to the generate_music tool rather than the listing tool.

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 sufficiently conveys what comes back (models, their controls, and cost). An agent lacks exact response shape, but that is a minor gap for a simple discovery call.

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 zero parameters, so there are no parameter semantics to document; baseline for a 0-param tool applies. Nothing in the description is needed to explain inputs.

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 ('music models') plus what is returned ('their controls and credit cost'). The 'music' qualifier cleanly distinguishes it from siblings list_image_models and list_video_models without needing their schemas.

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?

Usage is only implied: an agent can infer this should be called to discover models before generate_music, but the description never states when to use it versus get_image_model/get_video_model or alternatives. No exclusions or prerequisites are given.

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