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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds a genuinely useful default ('omit it for the 20 newest') and the 50-video cap, but says nothing about rate limits, the default date window, or pagination/truncation behavior for large accounts.

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 sentences, metrics front-loaded, then the parameter behavior. No filler, no restating the title, and the most decision-relevant constraint (the 50-video cap and default set) is packed into the second sentence.

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?

With no output schema, listing the returned metrics is essential and it does so. The remaining gap is the date window: the schema says 'give both dates or neither' but the description never states what window applies when both are omitted.

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 the baseline is 3, but the description adds meaning the schema lacks: videoIds is a comma-separated list sourced from list_posts, and omitting it selects the 20 newest videos. That default is not documented anywhere in the input schema.

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?

Specific verb (Return) plus an explicit enumeration of the metrics returned (views, watch time, average view duration and percentage, likes, comments, shares, subscribers gained) and the resource scope (up to 50 videos over a window). This clearly separates it from the sibling get_youtube_channel_insights, which operates at channel level.

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?

Gives concrete operating context: videoIds comes from list_posts, and omitting it returns the 20 newest videos. It stops short of naming the alternative tool (channel insights) or stating when this tool is the wrong choice.

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