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

Annotations already declare destructiveHint=true, idempotentHint=false, and readOnlyHint=false, so the safety profile is covered; the description usefully adds that only one comment sits above all others and that ownership of the post is required. It does not state outright that pinning a second comment displaces the existing pin, nor what the response looks like, leaving some mutation behavior to inference.

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 core action is front-loaded, but the second sentence largely restates the first ('Pins one comment ... or unpins it' after 'Pin a comment ... or unpin it'). Two of the three sentences cover the same ground, which is wasted space even though the total length is short.

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 only two parameters, full schema coverage, annotations, and no output schema, the description covers ownership scoping, the one-pin-per-post rule, and the error case adequately. The remaining gap is whether an existing pin is replaced or preserved, which an agent would want to know before calling a destructive operation.

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% and the `unpin` boolean already documents its own default, so the schema does the heavy lifting. The description gestures at the unpin mode in prose but adds no format, ordering, or edge-case detail beyond what the schema states.

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 names a specific verb+resource ('Pin a comment') and pins down scope: 'one comment on a post of your publication above all others,' plus the asymmetry that comments on other people's posts error out. That is enough to separate it from like_comment, reply_to_comment, or delete_comment, though it never names a sibling for routing.

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?

'or unpin it' and 'a comment on someone else's post returns an error' give clear use context and one concrete failure condition. It lacks explicit when-not guidance or a pointer to which tool to use instead for the adjacent operations, so it stops short of 5.

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