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

The description supplements annotations by detailing the return format, error scenarios (empty text, disabled comments, missing video), and the fact that it creates a new resource. Annotations already indicate mutation and non-destructiveness, and the description adds context about what the tool does and its failure modes.

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 concise and well-structured with clear sections (Args, Returns, Examples, Errors). Every sentence adds value, and the first sentence immediately states the purpose. No redundancy or fluff.

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 write tool with only 2 parameters and no output schema, the description covers the operation, example usage, return data, and common errors. It does not mention authentication or rate limits explicitly, but the error note on quota covers some of that. It is largely complete for the given complexity.

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 coverage is 100%, so baseline is 3. The description adds minimal extra value: it mentions that text supports basic HTML entities, which schema does not. Otherwise, parameter descriptions are nearly identical to schema. The return format and example provide indirect parameter 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?

The description clearly states the tool posts a new top-level comment on a YouTube video, creating a new comment thread. It uses a specific verb and resource, and distinguishes from siblings like youtube_reply_to_comment (which replies to an existing thread) and youtube_list_comment_threads.

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 an example and lists error conditions, which imply use cases, but it does not explicitly state when to use this tool vs alternatives like youtube_reply_to_comment. There is no direct contrast or prerequisites mentioned beyond the schema.

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