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

With no annotations, the description carries the full burden and does well: it discloses that payment happens out-of-band by a human on the hosted page, that activation is automatic and asynchronous, and that the agent should poll get_account. It does not cover auth requirements, whether repeated calls create multiple checkout sessions, or expiry of the URL.

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?

Two tight sentences, front-loaded with the return value (checkout URL) and followed by the activation flow; every clause earns its place with no filler.

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 tool with no output schema and no annotations, the description adequately covers the return value, the human-in-the-loop payment step, and the follow-up check. It leaves gaps on error/edge behavior (already subscribed, abandoned checkout) and the period parameter.

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 0%, so the description must explain both parameters and does not: the 'period' monthly/annual option is never mentioned. Worse, it names the plans 'Starter or Business' while the enum values are starter/pro, introducing a label that conflicts with the schema rather than clarifying it.

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 concrete verb+resource ('Get a hosted checkout URL') for upgrading to a paid plan, which cleanly separates it from siblings like get_billing_portal, sign_up and get_account. Minor deduction because it labels the plans 'Starter or Business' while the schema enum is starter/pro, so the agent cannot fully trust the plan vocabulary.

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?

Usage is implied clearly (call this to begin a paid-plan upgrade) and it names get_account as the post-payment verification step. However it gives no when-not guidance, no mention of get_billing_portal as the alternative for managing an existing subscription, and no prerequisite/eligibility conditions.

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