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

readOnlyHint=true already tells the agent this is a safe, side-effect-free read. The description adds genuinely useful context beyond that — the call is free and video entries carry plan-gating info — but says nothing about result size, ordering, or whether it's cached.

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?

A single 90-character sentence with the cost signal front-loaded and no filler. Every clause earns its place by naming the returned attributes.

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?

With no output schema, the description carries the return-value burden and does list the key fields (kind, credit price, plan unlock). It stops short of describing ordering or entry count, but for a zero-param catalogue lookup it is close to sufficient.

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 is nothing for the description to clarify beyond what the schema provides; baseline 4 applies. The stated return fields are a bonus, not a param explanation.

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 names a concrete resource (models) and enumerates what each entry contains: kind, credit price, and plan-gated video access. That cleanly separates it from the other list_* siblings (characters, flows, voices) without naming them explicitly.

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?

'Free' implies this is the cost-checking lookup to call before spending credits on generate_* tools, but the description never states when to reach for it versus list_flows/list_voices or confirms there are no filters to apply. Usage is inferable rather than stated.

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