youtube-mcp

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

With no annotations provided, the description carries full burden and does well by disclosing key behavioral traits: the quota cost (50 units), file format requirements (JPEG, PNG, GIF, BMP), and size limit (max 2MB). It clearly indicates this is a mutation operation ('Upload') and provides practical constraints, though it doesn't cover authentication needs or error conditions.

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 perfectly structured with a clear purpose statement upfront, followed by cost information, then parameter explanations in a labeled 'Args' section. Every sentence earns its place with no wasted words, making it easy to scan and understand quickly.

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?

Given the tool's moderate complexity (2 required parameters, mutation operation) and the presence of an output schema (which handles return values), the description is quite complete. It covers purpose, cost, parameters, and file constraints. The main gap is lack of explicit sibling tool differentiation, but overall it provides sufficient context for effective use.

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 0% schema description coverage for both parameters, the description compensates by explaining that video_id identifies the target video and file_path must be an absolute path to a thumbnail image. It adds meaningful context about file format and size constraints that aren't in the schema, though it could specify video_id format or path examples.

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 specific action ('Upload a custom thumbnail') and target resource ('for a video'), distinguishing it from sibling tools like update_video or upload_video which handle different video modifications. It provides a precise verb+resource combination that leaves no ambiguity about the tool's function.

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 usage context through the quota cost mention and file format constraints, but does not explicitly state when to use this tool versus alternatives like update_video (which might handle thumbnails differently) or provide clear exclusions. It offers some practical guidance but lacks explicit comparison with sibling tools.

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