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

Annotations declare a non-readonly, non-destructive, non-idempotent, open-world operation, and the description adds genuinely useful context beyond that: "Never charges the card," the 30-minute single-use link lifetime, and the billing:read / billing:write permission requirements per action. That directly resolves the main fear an agent would have about a billing-adjacent tool, though it doesn't state what happens to a previously issued link.

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 text is dense and front-loaded, with each action clause carrying distinct information and the safety statement placed early. The opening noun fragment is slightly awkward, but no sentence 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?

For a 3-parameter mutation tool with no output schema, the description covers the action branches, safety guarantee, link lifetime, and per-action permissions, which is most of what an agent needs to invoke it safely. The remaining gap is parameter/action interaction, not core behavior.

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%, so the description must carry parameter meaning; it partially does by explaining that tier and interval are omitted to select the current plan for confirm_link. The enum values are self-describing, but the description says nothing about how tier/interval interact with action=list or whether supplying them with confirm_link changes the target plan, leaving a real gap.

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 opening fragment "Plans and the paid-plan link" is a noun phrase, not a verb+resource statement, but the per-action clauses do specify outcomes: action=list returns plans, prices, and the charge today; action=confirm_link produces a single-use 30-minute link. What's missing is any differentiation from close siblings like get_subscription, upgrade_subscription, or downgrade_subscription, so an agent cannot tell from the text which tool owns plan changes.

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?

The action clauses imply when each branch applies, and "omit tier and interval to start the current plan" is a concrete usage rule for confirm_link. However, no guidance is given on when to prefer this over upgrade_subscription/downgrade_subscription, or whether list should be used before confirm_link, leaving the sibling-selection decision to inference.

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