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

Annotations already declare readOnlyHint, idempotentHint, and non-destructive behavior, so the safety profile is covered. The description adds genuinely new behavioral facts: the output is a single image contact sheet rather than a list, and atSec is capped at 12 timestamps with even-spread defaulting. It stops short of saying what happens for a static image (are timestamps ignored?) or whether failures are surfaced per-moment.

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 sentences with zero filler: the first front-loads what the tool does and returns, the second covers the one parameter behavior an agent cannot infer. Nothing is repeated from the annotations or title.

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?

With annotations carrying the safety profile and no output schema, the description carries the return-shape burden itself and does so explicitly (one image, labelled cells). For a three-parameter read tool, an agent has enough to invoke it correctly aside from minor edge cases like image (non-video) inputs.

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 67% and the description covers the only undocumented non-trivial parameter semantics that matter: atSec caps at 12 and, when omitted, moments are spread evenly over the clip — a default behavior absent from the schema. The 'id' parameter still gets no explanation (media id vs composition id?), which keeps this below top marks.

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 ('looks inside an image or video') and, crucially, what it produces: one contact sheet with each requested moment as a labelled cell. This distinguishes it functionally from sibling retrieval tools like get_media and list_media, which the agent can tell apart without opening either schema.

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?

Explains the atSec argument's intended use (spread moments evenly when omitted), which implies when the tool is useful. However, it never explicitly says when to choose this over get_media versus when not to, or what preconditions (e.g. valid media id from list_media) are needed, so routing guidance is only implied.

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