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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds the important behavioral fact that results are "filtered to what this user's plan actually allows" — a plan-gating trait not in the annotations. "Reads nothing and costs nothing" reinforces safety/cost but is largely redundant with readOnlyHint, so it stops short of a 5.

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 sentences, front-loaded with purpose before the call conditions, with no filler. The long enumeration of option categories is slightly list-heavy but every item conveys a real return dimension, so it earns most of its space.

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 compensates by enumerating what the response contains (orientations, formats, length ceiling, styles, paces, languages, voice catalogue), and annotations cover the safety profile. An agent has everything needed to call and interpret it.

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 description coverage is 100% and all three parameters carry enum values and descriptions, so the schema already documents filtering fully. The description adds no syntax or format detail beyond what the schema provides, making the baseline 3 correct.

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 states a specific resource tied to a sibling tool ("Everything create_video can be set to") and enumerates the concrete dimensions returned (orientations, formats, length ceiling, styles, voices). An agent can tell this is a lookup/options-listing tool distinct from create_video without opening either 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?

It gives explicit triggers: "Call this before making a video when the user wants to choose rather than have you decide, when they ask what voices or styles exist, or when you are about to guess at a value." It names the related action (making a video) and the condition that selects this tool, leaving little to inference.

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