Upgrade plan

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

The annotations already indicate non-readonly, non-destructive, but the description adds critical financial behavior: agents never pay directly, returns a Stripe Checkout URL for the human, and 'Nothing is charged until your human pays.' This beyond-annotation transparency is essential to prevent an agent from taking harmful action. No contradiction.

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 but information-dense, front-loaded with the main purpose, then the usage pattern, then edge cases. Every sentence adds value: admin-only restriction, listing flow, Stripe payment, downgrade handling, and member message. No fluff or repetition.

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?

With no output schema, the description fully covers the three possible return scenarios (new subscriber → Stripe URL, existing paid/downgrade → instructions, member → message), plus permission handling. An agent has all information needed to call correctly without ambiguity.

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 100%: both 'plan' and 'period' are well documented, including the default and the 2-months-free bonus. The description reinforces the omit-to-list behavior already present in the schema, adding no new parameter semantics. Baseline 3 is appropriate since schema carries the full weight.

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 specific verb and resource ('Change this account's SUBSCRIPTION plan'), notes 'admin only', and clearly distinguishes from siblings like billing_status or buy_credits by describing the flow: list plans with no argument, then set a plan. The purpose 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?

Explicitly instructs the two-step call pattern ('Call with no argument to list the plans... call again with `plan` set'), and specifies the fallback for paid/downgrade cases (returns instructions) and for members ('ask an admin' message). This fully clarifies when to use the tool and what to do in each scenario.

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