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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so safety is covered. The description adds real context beyond them: only public channels are supported, results are ordered most-recent-first, and the three projection parameters exist to reduce payload size. It stops short of describing pagination or error behavior.

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, front-loaded with the core behavior and free of filler. The second sentence is slightly redundant in listing three parameter names the schema already defines, but it earns its place by explaining why they exist.

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 read-only, single-required-parameter listing tool with full schema coverage and no output schema, the description covers what the agent needs to call it. The item_fields and data_fields enums already expose the returned payload shape (content, likeCount, replyCount, image, attachment), so omission of return-format prose is acceptable; pagination behavior is only implicit.

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 description coverage is 100%, so every parameter is already documented in the schema, including the cursor pagination contract and the channelId-vs-handle override. The description only names projection_preset, data_fields and item_fields and gives their shared rationale (payload reduction), adding little beyond the existing 'Add top-level data keys on top of the selected projection_preset' text. Baseline 3 applies.

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?

States a specific verb and resource ('Returns a public YouTube channel's posts') plus ordering ('most recent first'), which distinguishes it from youtube_get_channel_videos and youtube_get_post. It never names those siblings explicitly, so an agent must infer the posts-vs-videos distinction from the resource word alone.

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?

There is no when-to-use statement, no prerequisites, and no named alternative despite many close siblings (youtube_get_channel_videos, youtube_get_channel_shorts, youtube_get_post). The word 'posts' implicitly scopes the tool, but nothing tells the agent when to prefer it over the other channel-content tools.

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