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

With no annotations supplied, the description carries the full behavioral burden, and it does disclose valuable non-schema traits: presets are "instant, free" while prompt generation takes ~30–90s and is presumably metered. However, it never says whether the added animation replaces or appends to existing animation, whether the call is synchronous or returns a job to poll (relevant given the wait_for_job and list_jobs siblings), or what a failed generation does to credits.

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 dense sentence, front-loaded with the action and then enumerating the three modes with their tradeoffs. It is efficient and scannable. The one waste is listing all 17 preset values inline, which is a pure duplication of the schema enum and consumes most of the character budget.

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 mutation tool with no annotations and no output schema, the description leaves important gaps: no mention of the return value or whether a job must be polled, no explanation of `id` vs `name`, and no statement about how a new animation composes with existing ones. The three-mode framing is the essential part and it is present, so this is adequate but not complete.

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 only 50%, and the description mostly mirrors what the schema already encodes: the preset enum is repeated verbatim, adding no meaning beyond the enum itself. It does add real value for `prompt` via the worked example and latency note, and frames video_url as a performance reference. It says nothing about `id` (presumably the mascot to animate) or `name`, leaving two parameters undocumented in both places.

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 opens with a specific verb+resource ("Add an animation") and immediately splits the tool into its three input modes: preset, prompt, and video_url reference. An agent can tell what the tool produces without reading the schema. It stops short of naming a sibling (e.g. suggest_animations) as the alternative path, so the differentiation is implicit rather than explicit.

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?

Clear routing among the three mutually exclusive input modes: presets for instant/free canned motions, prompt for custom motion at a stated cost (~30–90s), video_url for performance reference. That is genuine when-to-use guidance for selecting parameters, which is the main decision this tool requires. It omits guidance on when to call suggest_animations first, and never states that only one of preset/prompt/video_url should be supplied.

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