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

Annotations declare a non-read-only, non-destructive, closed-world write, and the description adds genuinely non-obvious context beyond that: the add-on is billed monthly and, when the site is already paid up, the remaining days are charged immediately. That proration/money-impact disclosure is exactly the kind of behavior an agent should surface to a user. It does not state idempotency (what happens on a repeat call) or any permission requirement.

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, front-loaded with the action and its valid values, then billing behavior, then the sibling redirect. The parenthetical value list mildly duplicates the enum, but nothing else is wasted.

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?

A simple two-parameter tool with annotations and no output schema needs little more than this: what it does, what it costs, and where to go for the adjacent case. The only meaningful omission is repeat-call behavior and any hint of how to verify the add-on was applied.

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%: 'site' is documented in the schema as a slug or id, while 'addon' has only an enum. The description restates the enum values but adds no meaning about what no_badge or extra_storage actually enable. With half the parameters documented structurally and the other half covered only by an enum, this sits at the baseline.

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 ("Turn on a monthly add-on") and enumerates the two valid add-ons inline. It also explicitly routes custom domains to add_custom_domain, so an agent can distinguish it from that sibling without opening either schema.

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?

The when-to-use case is clear (enabling a monthly add-on for a site) and one alternative, add_custom_domain, is named explicitly. It stops short of covering related siblings such as remove_addon or list_addons, so there is no guidance on what to do if the add-on is already active or how to check first.

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