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

Annotations already declare destructiveHint=true, idempotentHint=true and readOnlyHint=false, so the description only needs to add context — and it does: it discloses the state precondition that governs failure and that no credits are charged for cancelled posts. It does not say what happens to a cancelled post afterwards (recoverable/reschedulable) or what an error looks like, which keeps it below a 5.

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?

Three short sentences, each carrying distinct information: what it does, when it fails, and the cost implication. The primary action is front-loaded and there is no 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?

For a one-parameter mutation with no output schema, the description covers purpose, eligibility, and cost side effects, which is most of what an agent needs. It leaves open the post-cancellation state (whether the post disappears or can be rescheduled) and the source of post_id.

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 0% — post_id is documented only as an integer with minimum 1 — and the description adds nothing about it: no indication of where to obtain a valid post_id or that it must refer to a scheduled/failed post. For a single-parameter mutation this is a real gap, since an invalid or ineligible id is the most likely failure mode.

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 ('Cancel') plus the resource ('a post') and narrows the eligible state to scheduled or failed posts. An agent immediately understands this is a state-gated cancellation operation, not a generic delete.

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?

It clearly states the positive condition (still scheduled, or failed) and the exclusion (already uploading or posted cannot be cancelled), which is the key decision boundary for this tool. It does not point to any alternative action for the non-cancellable cases, so it falls just short of the top mark.

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