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

Annotations already cover the safety profile (readOnlyHint, openWorldHint), and the description still adds real value: it discloses the credit cost, the exact return fields, and that poll questions/options live under `raw`. That last detail is behaviorally useful and not derivable from annotations or schema.

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?

Four short sentences, each carrying distinct information: purpose, return contents, structural hint about `raw`, and cost. Front-loaded and free of filler.

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, the description correctly takes on the job of describing the return shape (text, attachments, likes, comment count, `raw` polls) and adds cost. The only missing piece is any explanation of `cache_max_age`, which leaves one parameter opaque for a caching-sensitive call.

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 50% — `url` is documented in the schema and the description reinforces it with the permalink form and bare-id alternative. `cache_max_age` is undocumented in both places, so the description neither compensates for the gap nor adds format detail beyond the 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?

The description gives a specific verb+resource ('One community post by id or permalink') and enumerates the returned payload (text, attachments, likes, exact comment count), which clearly separates it from the listing sibling youtube_channelCommunityPosts. It stops short of naming that sibling explicitly, so the differentiation is implied rather than stated.

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?

Usage is only implied: the phrase 'by id or permalink' signals that the caller must already have an identifier, which hints at fetching after a listing call, but no when-to-use or when-not-to-use guidance is given. There is no mention of youtube_channelCommunityPosts as the way to obtain ids, and no exclusion for posts that are actually videos.

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