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

Annotations already declare readOnlyHint=true, openWorldHint=false, destructiveHint=false, so the safety profile is covered. The description adds useful operational context -- the default of 6 frames, that times are in seconds, and that a combined sheet is cheaper to view -- but says nothing about limits (max 24) or the return payload shape.

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 tight sentences with the purpose front-loaded and no filler; the sheet/cost note is earned because it affects tool-choice economics. Slightly dense but nothing wasted.

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 read-only, no-output-schema tool with 7 params, the description covers purpose, the two frame-selection modes, defaults, and the sheet trade-off, while deviceId/workSessionId/width are documented in the schema itself. Nothing critical to calling it correctly 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 only 43%, so the description must compensate, and it does for the key inputs: 'count of evenly spaced frames (default 6)', 'times in seconds', and 'sheet combines them into one labelled contact sheet'. This resolves the unit ambiguity and default that the bare schema leaves open; only width and path remain unaddressed in prose.

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?

Names a specific verb and resource ('returns still frames as images') and states the intent ('see what happens and pick cut points'), which clearly separates it from video_transcribe or video_info. It stops short of explicitly naming a sibling to contrast against, so it lands just under the top score.

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 'pick cut points' phrasing implies when the tool is useful and the sheet note implies when to prefer the contact-sheet mode, but there is no explicit when-to-use vs alternatives guidance (e.g., 'use video_info for metadata instead'). Usage is only implied.

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