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

Annotations already declare this is a non-read-only, non-destructive, non-idempotent, closed-world operation. The description adds real behavioral context on top: that the session is hosted by Stripe, that the interval defaults to year, that a 7-day trial applies, and that the caller receives a URL to open rather than a completed subscription.

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 short sentences, no filler, with the core action stated first and the return value last. Every clause carries information the agent cannot get from the schema or annotations.

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?

The description covers the mutation's effect and its return value despite there being no output schema, which is the most important gap closed. It is still thin on prerequisites (must an account exist first?), on whether repeated calls create duplicate sessions, and on what the owner does with the URL, which matters for a creation tool that is explicitly not idempotent.

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 0% and both parameters are enums, so the schema only lists values. The description compensates partially by explaining the interval default ('year') and the trial period, but it says nothing about what 'standard' versus 'plus' plans mean or whether the selected interval changes trial eligibility.

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 gives a specific verb and resource ('Creates a hosted Stripe Checkout session for a plan'), which is far more precise than the tool name alone. It does not explicitly distinguish itself from sibling tools like subscribe or start_account, so an agent must infer the boundary, but the purpose itself is unambiguous.

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: this is the tool that produces a checkout URL so an owner can complete a purchase. There is no explicit when-to-use or when-not guidance, and the closely related sibling 'subscribe' is never referenced, leaving the agent to guess which entry point to pick.

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