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

Annotations declare readOnlyHint/idempotent/non-destructive, and the description reinforces this with the crucial disclosure that the tool "does NOT generate anything, charge anything or need an account" — preventing an agent from misreporting a charge. It also discloses the downstream flow (URL on malfoid.tv/cast, a pass holder films in Create) and the pass requirement, which no annotation conveys.

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?

The core action, the return value, the no-charge/no-account caveat and the character routing all appear in a logical order with a concrete example. It runs long and the opening phrase "makes a short vertical AI video" sits in slight tension with the later "does NOT generate anything," costing a little crispness, but no sentence is pure filler.

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 an 8-parameter tool with an output schema, the description covers what an agent needs: what the URL is, what to tell the user, that filming requires a pass, and how to choose between premade and custom characters. Return-value details are delegated appropriately to the 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?

Schema coverage is 100%, so enum meanings (vibe, style, camera, seconds) are already documented and the description rightly does not repeat them. It does add real routing logic beyond the schema: use character="malfoid" or "malfoid,leo" for premade cast, and character_name plus character_description for anyone else, with the note that the user designs that character first.

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?

Opens with a specific verb and artifact: "Build a one-tap link that makes a short vertical AI video of a character doing what the user describes," with an inline example. It is immediately distinguishable from siblings get_prices, get_showcase and list_characters, and it explicitly routes to list_characters for supported premade cast.

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?

"Use this whenever the user asks for an AI video, short, clip, TikTok/Reel/Shorts-style video, or animation of a character" gives explicit trigger conditions, and the description names the alternatives: list_characters for premade slugs, story cards for other cast members, and the credit-paid path for longer videos or custom characters.

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