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

Annotations already declare readOnly, idempotent and openWorld, so the safety profile is covered. The description adds real value by specifying that frames are full-resolution and captured at precise moments between keyframes, which is behavioral detail the annotations cannot express.

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 tight sentence with the core action front-loaded and the rationale trailing it. Every clause earns its place.

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 a two-parameter read-only tool with a fully described schema, almost everything an agent needs is present. The one residual gap is that no output schema exists and the description doesn't say what comes back per timestamp (image format, one frame per entry), which an agent may wonder about.

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 100%, so both 'url' and 'timestamps' are fully documented, including the 1–6 count and seconds-from-start units. The description's 'at specific moments' adds nothing beyond that, so the baseline of 3 applies.

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: 'Grab full-resolution frames at specific moments of a reel'. That distinguishes it from reel_transcript and from watch_reel's broader sampling, though the siblings are never named explicitly.

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 clause 'to read small on-screen text or check a detail between keyframes' gives a concrete use case that explains why an agent would reach for this instead of the keyframe-level view. It stops short of stating prerequisites or when not to use it, and leaves the relationship to watch_reel to the schema.

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