youtube_set_thumbnail

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

No annotations are provided, so the description carries full responsibility for disclosing behavioral traits. It does not mention that this is a mutating operation, whether it overwrites an existing thumbnail, requires video ownership, or has any side effects. The description only focuses on the input parameters, leaving the tool's behavior opaque.

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?

The description is extremely concise: a single action sentence followed by two brief parameter lines. Every word earns its place, and the format is front-loaded with the primary action immediately visible. There is no fluff or repetition.

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 simple mutation tool, the description is minimally adequate: it states the purpose, parameters, and file constraints. However, it omits important context such as authentication requirements, the fact that it modifies a video's metadata, or what the result of the operation is. With no output schema and no annotations, the description could be more complete.

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 schema description coverage at 0%, the description compensates well by explaining each parameter: 'video_id: YouTube video ID' and 'file_path: Absolute path to the thumbnail image (JPEG, PNG, GIF, BMP; max 2MB)'. This adds meaningful constraints and formats beyond the bare schema, though it could be further improved with examples or additional details like file path handling.

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 clearly states the tool's function: 'Upload a custom thumbnail for a video.' It uses a specific verb and resource, and this action is distinct from sibling tools like youtube_upload_video or youtube_update_video, which handle broader video operations. No ambiguity remains about what this tool does.

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 provides no guidance on when to use this tool versus alternatives, nor does it mention prerequisites such as authentication or ownership of the video. It only describes the action, leaving the agent to infer usage context from the tool name and sibling list.

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