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

With annotations only declaring the safety profile (readOnlyHint=false, destructiveHint=false, idempotentHint=false, openWorldHint=true), the description adds substantive behavior: it returns a Stripe checkout URL, it does not charge the user, and for already-paid accounts it diverts to the billing page. Those are exactly the side-effect details an agent needs and none are available in structured fields.

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, front-loaded with the action and the destination of the result, with the pricing parentheticals carrying real decision value for the agent. Slightly dense with dollar figures, but nothing is redundant with the schema.

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?

For a two-parameter mutation with no output schema, the description covers what is returned (checkout URL), what happens in the alternate account state (billing page), and the required pre-step (ask for the plan). Nothing needed to call it correctly is missing.

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%, and the description compensates by defining the meaning of each plan value, including the monthly price and overage rate, which the bare enum does not convey. The account_id parameter is only covered by the schema's "From api_account" note, so the description does not fully close the coverage 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?

The description names a specific verb and resource ("Start an upgrade of the signed-in person's GolfCore API account") and enumerates the two target tiers with pricing, so the agent knows exactly what the tool does. It does not, however, distinguish itself from the sibling subscribe_premium, leaving a plausible ambiguity about which upgrade path applies to which product.

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 clear operational context — ask which plan the person wants before invoking, and the tool returns a billing page rather than an upgrade when the account is already paid. There is no explicit exclusion or named alternative tool, so it stops short of a 5.

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