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

Beyond the readOnlyHint annotation, the description discloses the downstream consequence of an upgrade (card on file is charged), where confirmation happens (dashboard only), and that proration is computed there. It also enumerates the returned dimensions: tier, monthly sticker, eligibility and reason. This is the kind of context annotations cannot carry.

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?

Front-loaded with the core answer (what the tool returns) before the caveats, with no filler. The sentences are dense and clause-heavy, which costs a little readability, but every sentence carries information an agent needs.

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?

No output schema exists, so the description must convey the return shape, and it does: tiers, monthly prices, eligibility and denial reasons, plus the note that the exact amount due is not returned here. Combined with the readOnly annotation and single documented parameter, an agent has everything needed to call it correctly.

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?

Only one parameter, and the schema documents it fully (100% coverage: 'The hosting site's domain'). The description reinforces the per-site scope ('one of the customer's hosting sites') but adds no syntax, format, or accepted-value detail beyond the schema. 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 resource and scope: the higher plan tiers a single customer-owned hosting site can move to, including price and eligibility with reasons. This is functionally distinct from catalog/pricing siblings, but no sibling is named, so an agent must infer the split from wording 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?

Gives explicit trigger phrasing ('can I get a bigger server?', 'what would it cost to upgrade?') and an explicit boundary: the exact prorated amount due is shown only in the dashboard, and the charge is confirmed there, never by a tool. That tells the agent both when to call this and what it must not attempt.

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