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

Annotations already declare readOnly/idempotent/non-destructive and closed-world, so the safety profile is covered. The description adds genuinely new behavior: a guest call returns 401 and triggers the OAuth flow, and payment is a browser-side action rather than a tool side-effect.

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?

It is short and front-loads the return value before the payment/auth caveats, but the second clause of the first sentence ('ninety-day stats with the shelf beside the card') is cryptic filler that costs comprehension.

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 one parameter, no output schema, and annotations carrying the safety profile, the description supplies the missing pieces an agent needs: what is returned (premium details plus a payment link) and the auth/401 behavior. Only the premium feature list remains elliptical.

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?

There is a single parameter with 100% schema description coverage, so the schema fully documents 'domain'. The description adds no further meaning about the parameter, making the baseline 3 appropriate.

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 does convey that the tool returns what premium adds and the payment link for the card owner, but the phrasing is jargon-heavy ('ninety-day stats with the shelf beside the card') and never states a clean verb+resource. It does not clearly distinguish itself from near siblings like atlas_owner_card or atlas_owner_stats.

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 gives a concrete exclusion — checkout is a card form in a browser, not an agent action — which tells the agent this tool surfaces a link rather than performing payment. It also states the signed-in account requirement and the 401/OAuth guest behavior, though it names no explicit alternative sibling.

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