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

Annotations already declare readOnlyHint=true and destructiveHint=false, but the description adds meaningful behavior beyond them: you cannot pay on the user's behalf, payment is by card or PayPal, and whoami should be called afterward to confirm. It stops short of describing output/pagination, but the added context is substantial.

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 return value, then usage triggers, then the human-in-the-loop constraint, then the verification step. Every sentence carries a distinct instruction and none 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?

With an output schema present, return-value detail is not needed, and annotations cover the safety profile. The description fully covers when to call it, what the agent can and cannot do, and what to do afterward.

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 description coverage is 100%, so the single 'plan' enum parameter is already fully documented ('omit to get a link for every paid plan'). The description's 'a checkout link for each' corroborates but adds no syntax or format detail beyond the schema, matching the baseline 3.

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 ('Returns') and three concrete resources: the user's current plan, the paid plans with price/credits/projects, and a checkout link per plan. An agent can distinguish this from get-analytics or whoami siblings immediately.

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?

Explicit triggers: user asks to upgrade/change plan/buy credits, or a tool reports a needed paid feature or exhausted credits. It also names the follow-up (call whoami after payment) and the flow constraint (the user opens the link themselves).

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