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

With no annotations, the description carries the full load and does substantial work: it discloses that no charge occurs at call time, that the resulting plan is a recurring subscription until cancelled, and that the agents plan requires the owner to tick a consent box on the payment page. Missing are auth requirements, whether repeated calls create duplicate links, and link expiry.

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?

Four short sentences, front-loaded with the resource and its key constraints, with no filler. The opening is a verbless fragment and the semicolon chaining is dense, but nothing 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?

An output schema exists, so return structure need not be explained, and the description covers the salient behavioral facts an agent needs: no immediate charge, recurring billing, and the consent requirement. Only currency semantics and call-repetition behavior are left unaddressed for a 5-parameter tool.

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 compensate, and it does for plan (starter/agents), billing (month default or year) and the site/email pairing. It says nothing about the currency parameter, which is one of five left entirely undocumented.

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 identifies the resource precisely as a checkout link pre-filled with the plan, site and email, and adds the concrete plan values (starter or agents) that the schema leaves unenumerated. It does not name a sibling to differentiate from, but the contrast with start_free_test/get_plans is implicit in the paid-checkout framing.

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 useful post-call workflow guidance ('hand the link to the user, who checks it and pays on the payment page') but never states when to pick this over start_free_test or get_plans, nor any precondition for creating a checkout. Usage is implied rather than routed.

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