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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=false, so safety is covered. The description usefully adds that the output is an image (not a URL or metadata), but says nothing about image format, sizing behavior, or what happens if the time exceeds the media duration.

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 front-loaded sentence with no filler. It is efficient, though the brevity comes at the cost of the missing usage and parameter detail noted elsewhere.

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 no output schema, the description does note the return type (an image), which is the key missing piece. However, two of four parameters lack documentation and there is no guidance on alternatives, so it is adequate rather than complete for a tool with four 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 50%: project and media are documented in the schema, but 'at' and 'width' are not. The phrase 'source time' gives a small hint that 'at' refers to media time rather than timeline time, but 'width' is entirely unexplained and the description adds little else over the schema.

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 resource (one frame of a video or image) and the result (returned as an image), so the agent knows exactly what it produces. It does not differentiate from near-neighbors like filmstrip, show_preview, or look, which all return visual output.

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?

There is no guidance on when to use this versus filmstrip, show_preview, or look, all of which can surface imagery. The phrase 'at a source time' hints at a use case but no explicit when/when-not is given.

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