set_coverSet or clear a clip's cover image using a finished cover generation or an uploaded media key to control its thumbnail.
Set a clip's cover (thumbnail): a finished cover generation, an uploaded image key, or clear it.
| Name | Required | Description | Default |
|---|---|---|---|
| key | No | An image key from upload_media. | |
| clear | No | ||
| clipId | Yes | ||
| generationId | No | A finished cover.drafts / cover.hd generation. |
Changes observed during successful MCP inspections.
v0.1.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already disclose the safety profile (readOnlyHint=false, destructiveHint=true, idempotentHint=true), so the bar is low, but the description adds almost nothing beyond them: it does not say that setting a cover replaces an existing one, that clearing removes the thumbnail, or that generationId/key must be mutually exclusive. It is at least consistent with the destructive hint via 'clear it'.
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 sentence with the modes front-loaded and no filler. Slightly telegraphic ('an uploaded image key') but every clause maps to a distinct behavior, so nothing is 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 destructive, 4-parameter mutation tool with no output schema, the description should say what changes on success and how the three modes interact. It covers the modes but leaves replacement semantics and mutual exclusivity of generationId/key/clear unaddressed.
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?
With only 50% schema description coverage, the description carries real weight by mapping each mode to its parameter: 'finished cover generation' -> generationId, 'uploaded image key' -> key, 'clear it' -> clear. Only clipId is left unexplained, which is self-evident from context.
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 (set) and resource (clip's cover/thumbnail) and enumerates the three input modes, so the agent knows exactly what the tool mutates. It does not name or contrast any sibling, but none of the siblings (upload_media, make_clip, ai_generate) directly overlap with this operation.
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 description implies three usage paths (finished generation, uploaded key, clear) and indirectly points at upload_media/ai_generate outputs, but it never states when to prefer one mode, whether modes are mutually exclusive, or any prerequisites for calling it.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.