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

Goes well past the annotations, which already declare readOnly/idempotent/non-destructive. The description discloses that the tool only returns a URL on cast.katechon.technology, that the user must open it and tap a button, that rendering happens in their private feed in ~30s (or minutes for a group scene), that nothing is generated, charged or account-gated at call time, and the free-vs-credits pricing boundary.

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?

Front-loads the core verb and the trigger phrase in the first two sentences, then layers output behavior, pricing and the character branches. It is denser than strictly necessary across five sentences and the pricing sentence is slightly tangential, but almost every line earns its place.

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 four enums and a deep schema, the description covers the remaining ambiguity an agent needs: the two mutually exclusive character paths, the free/paid boundary, and what the caller receives back. An output schema exists, yet the description still correctly frames the return as a link the human must act on.

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%, so the baseline is 3 and the description is not required to document enum values. It still adds selection logic the schema only partially carries: use the premade slugs for malfoid/thea/odette (up to 3), otherwise pass character_name plus character_description, and the cost/premium constraints tied to seconds.

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 and resource: 'Build a one-tap link that makes a short vertical AI video of a character doing what the user describes.' It is immediately distinguishable from the siblings (get_prices, get_showcase, list_characters), which are lookup/list tools, and it spells out the input shape (a described action plus a character).

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?

Gives a strong when-to-use trigger: 'Use this whenever the user asks for an AI video, short, clip, TikTok/Reel/Shorts-style video, or animation.' It also implicitly scopes the character branches. However, it never names an alternative tool or an explicit when-not-to-use case, so it falls just short of the top tier.

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