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

The description adds useful behavioral context beyond the neutral annotations: 'Takes a few minutes' signals latency, and the consent statement adds a legal precondition. However, it does not disclose whether the call returns a completed video or a job id requiring polling, and the annotations do not cover result handling.

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 front-loaded sentences with no filler. The core action comes first, the latency/consent details each earn their place, and the whole description is compact and easy to scan.

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?

There is no output schema, and the description never explains how the agent will receive the finished video or whether it must poll fattly_video_status. Given the 'takes a few minutes' hint and related sibling tool, this is a meaningful operational gap: an agent can invoke the tool but cannot confidently handle the result.

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% — all three parameters are already described in the schema. The prose description adds little beyond restating the consent requirement (already in the schema) and does not enrich parameter semantics further.

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 verb and resource: 'Turns a photo into a trend-style video from a preset.' It is clear enough to understand the tool's core function, but it does not explicitly differentiate it from siblings like fattly_animate_photo or fattly_generate_video, relying on the phrase 'trend-style' and 'preset' to carry the distinction.

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 description implies a use case (photo + preset + trend video) but gives no guidance on when to choose this tool over alternatives, and it never states when not to use it. No exclusions or sibling comparisons are provided, leaving the agent to infer selection.

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