Downloads only a chosen video segment and returns a timecoded contact sheet, so you can inspect what happens in that section at a glance without downloading the full video.
只下载这一段（例如 20 秒 ≈ 0.9MB），返回一张拼图，每格左上角烧着绝对时间码。 用于"看一眼这段画面在发生什么"。
| Name | Required | Description | Default |
|---|---|---|---|
| end | No | 20 | |
| url | Yes | ||
| cols | No | ||
| rows | No | ||
| start | No | 0 | |
| height | No |
Changes observed during successful MCP inspections.
v1.6.3Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations at all, the description does carry some real burden: it discloses the cost profile (only the segment is fetched, 20s ≈ 0.9MB), the single-image output form, and that timecodes are burned in. It omits what happens on fetch failure, how the grid dimensions affect output size, and whether the returned image is inline content or a file reference.
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 short sentences, front-loaded with the distinguishing behavior and a concrete size example that earns its place by conveying cost. The quoted colloquial use-case phrase is slightly informal but functional; nothing is padded.
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?
Because there is no output schema, the description's explanation of the returned contact sheet is genuinely needed and delivered. However, for a tool with six parameters, zero schema coverage, and zero annotations, the absence of any parameter-level guidance leaves the agent guessing on grid layout and resolution.
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?
Six parameters with 0% schema description coverage and no annotations, and the description only indirectly gestures at start/end via '这一段' and the '20 秒' example that matches the end default. cols, rows, height, and the url parameter are entirely unexplained, so the text fails to compensate for the schema gap.
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 output artifact (a tiled contact sheet with absolute timecodes burned into each cell's top-left corner) plus a scope constraint (only this segment is downloaded). This is far more specific than the bare name 'video_sheet', though it never names or contrasts the closest siblings such as video_frames or video_visual_scan.
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?
"用于'看一眼这段画面在发生什么'" gives an implied use case — quick orientation/overview of a clip — which is real guidance. But there is no explicit when-not condition, no mention of when to prefer video_frames / video_window / video_visual_scan, and no prerequisites (e.g. does the url need to be directly downloadable?).
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.