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

Annotations already declare readOnly, idempotent, non-destructive, closed-world, so the safety profile is covered. The description still adds real value beyond that: the call is free, it requires an API key or connected account, and it discloses eventual consistency ('plan changes from free to the plan bought, usually within seconds').

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?

Information-dense with no filler, but the opening sentence is a long comma-laden list of return fields that delays the when-to-use guidance into the third sentence. Front-loading the call triggers would improve it slightly.

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?

There is no output schema, so the description carries the return-value burden, and it does so thoroughly — enumerated fields, next-plan upsell data, and checkout_url. Auth requirements and the 'free' cost model round out what an agent needs 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?

The tool takes zero parameters, so there is no parameter meaning to add; a 4 baseline applies. The description correctly does not waste space on parameter syntax.

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-resource pair and enumerates the returned fields (plan, status, renewal date, cancel flag, price, this month's limit usage, next plan, checkout_url). It also explicitly differentiates from the nearest sibling: 'The same as get_account without the profile.'

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 when-to-use triggers: 'Call it before suggesting an upgrade, and after handing a human a checkout link to see when the payment went through.' It also names the alternative (get_account) and the condition that would select it, plus the constraint 'Free.'

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