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

Beyond the annotations, the description discloses the non-obvious economics: creating the link charges nothing, the user must open it and pay by card, and the checks are credited only when payment completes. That is precisely the behavioral context an agent needs to avoid telling a user they were charged, and it is consistent with readOnlyHint=false, destructiveHint=false and idempotentHint=false.

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 action and return value, then plan gating, then the critical no-charge caveat, then the prerequisite. No sentence is redundant.

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 single-parameter tool with an output schema and full annotation coverage, everything an agent needs is present: action, return value, plan constraint, payment flow, and where to obtain the pack key. Missing link-expiry detail is minor.

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% and the single `pack` parameter already names its source and example, so the description's "get the pack keys and prices from citation_topups first" mostly restates the schema. Baseline 3 applies since the schema carries the semantics.

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?

"Create a one-time Stripe Checkout link for a pack of top-up citation checks and return its URL" gives a specific verb (create), a specific resource (Stripe Checkout link), and the exact asset being purchased, which lets an agent distinguish it from citation_topups and citation_auto_reload without opening a 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?

It states the gating condition ("Paid plans only") and the required predecessor step ("Get the pack keys and prices from citation_topups first"), which is real when-to-use guidance. It does not say when an agent should prefer a different purchase path (e.g. auto-reload) or what to do if the plan is unpaid, so it stops short of full routing guidance.

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