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

Annotations already establish readOnly/idempotent/non-destructive, so the bar is lower. The description adds genuinely new behavioral context: it discloses that credit costs are merely estimated in the listing and that invoking it spends no credits, which is exactly the concern an agent would have before a paid generation flow. It does not describe pagination or response shape beyond the field list.

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 with no filler: the first enumerates what is listed, the second removes the main misreading (that this generates or charges). Front-loaded with the verb and resource.

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?

No output schema exists, but the description compensates by naming the returned categories (input modes, durations, resolutions, aspect ratios, credit-cost estimates). With zero params and annotations covering the safety profile, an agent has everything needed to call it correctly.

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 per the rubric the baseline is 4. Nothing in the description is needed to explain inputs, and it correctly implies no arguments are required.

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?

Specific verb ("List") plus concrete resource (Google Veo / xAI Grok video generation options) and an enumeration of the option categories returned. The closing sentence explicitly separates it from the sibling generate_video, so an agent can route without opening the 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?

The negative clause "Does not generate video or spend credits" implicitly routes the agent to generate_video/run_video_function for actual generation and signals this is the discovery step. There is no explicit "call this before generating" instruction, but the context is clear and no alternatives are named outright.

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