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

Annotations establish it is non-read-only, non-idempotent, non-destructive, and closed-world. The description adds genuine context beyond that: the multi-minute latency and the legal/consent obligation, both relevant behavioral traits for a costly generation call.

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?

Three short sentences, front-loaded with the core transformation, then latency, then the consent caveat. No wasted wording, though it is terse relative to the operation's complexity.

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?

No output schema exists, and the description does not explain what is returned or that this is an async job requiring polling via fattly_video_status – a notable omission for a minutes-long video generation. Latency and consent are covered, but the return/lifecycle pattern is missing.

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 all four parameters are already documented, including consent and the modelId/upload references. The description adds no format or syntax detail beyond the schema, so baseline 3 is appropriate.

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 concrete verb and transformation: 'brings a still photo to life as a video (adds motion)', which is specific and distinguishable from generic video generation. It does not explicitly name a sibling (e.g. fattly_generate_video) to draw the boundary, but the input+transformation is clear.

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?

Usage is implied – animate a still photo – and it warns the process takes minutes plus requires rights confirmation. However, it gives no explicit when-to-use vs alternatives such as fattly_generate_video or fattly_trend_video, leaving the routing decision to inference.

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