Pick a paid plan

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

Annotations only carry openWorldHint=true, so the description bears the burden and delivers: it discloses that an external browser page is opened, that payment happens outside the tool, that a link is returned, and that the operation is two-phase and non-idempotent. This is exactly the non-obvious behavior an agent needs before invoking a billing tool.

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 sentences, each load-bearing: what it does, how the two-step flow works, and the plan menu. The critical behavioral fact (opens a payment page, call again to finish) is front-loaded before the pricing detail.

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 no output schema, the description correctly states the return value (a payment link) and explains the resumption call. It omits edge cases such as what happens when a subscription already exists or whether the second call needs the same plan/company, which matters for a billing mutation.

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 100% but the schema descriptions are bare ("Plan", "The company's name"), so the description adds real value by mapping each enum value to price, seat count, and included features. The optional company parameter is never mentioned, leaving one small gap.

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 ("Starts paying for TeamOnly") plus the immediate side effect ("also ends a free trial"), which cleanly distinguishes it from the sibling start_trial. An agent can tell what this does and what it is not without opening the 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?

Gives an explicit sequencing rule that would otherwise cause failure: "The person pays there; call subscribe again afterwards to finish." The parenthetical about ending a free trial implies the relationship to start_trial, but it never names that sibling as the alternative, so it falls short of a full when/when-not statement.

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