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

Annotations already indicate it's a mutating operation (destructiveHint=true). The description adds value by explaining it returns Stripe checkout links (so the actual payment happens externally), and notes the presentation behavior ('Present monthly and annual options; default to the current plan'). This goes beyond the annotations without contradicting them.

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?

The description is compact yet informative. Each sentence earns its place: it opens with the core function, then usage conditions, then the alternative, then presentation preferences. No fluff, though it could be slightly tightened.

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 tool with an output schema absent, the description explains what it returns (checkout links) and when to use it. It also covers edge cases (trial, expired, lapsed) and defaulting. The only minor omission is a description of the actual response structure, but that's not required given the tool's simplicity.

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% — both 'plan' and 'interval' are fully described in the schema. The description adds some behavior guidance (e.g., 'default to the current plan'), but this is about tool behavior rather than parameter semantics, so it stays at the baseline 3.

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 clearly states the verb and resource: 'Return Stripe Checkout links ... to start or restore the paid subscription.' It also distinguishes itself from the sibling account_change_plan, making its unique purpose obvious without reading 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?

Explicit when-to-use is given: 'Use after a subscribe result or when the user asks to subscribe/pay/upgrade before having a subscription.' It also provides an exclusion: 'If the user already has an active Stripe subscription, use account_change_plan instead.' This is a model of clear routing.

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