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

The description goes beyond annotations by disclosing the human-in-the-loop payment requirement and the follow-up polling step. It clarifies that the agent cannot finish payment, which is critical behavioral context. No contradiction with readOnlyHint is present because preparing a link does not necessarily mutate state.

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 two sentences with no fluff. It front-loads the core action, then states the key limitation and the next step. Every word adds value.

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 a documented output schema, this description is fully sufficient. It explains what the tool does, what the agent must do next, and the human dependency, leaving no important gap for an agent to call and use it correctly.

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%, so the single parameter pack_id is already self-documenting. The description does not add extra semantic detail beyond the schema, but it also does not need to because the schema provides adequate meaning. Baseline 3 is appropriate.

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 tool's function: preparing a token purchase for a human principal and returning a checkout link. It also explicitly distinguishes this from completing payment, which is not possible for the agent. This makes the purpose unambiguous and distinct from sibling tools like check_limits.

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 description provides explicit usage guidance: use this to prepare a purchase, hand the checkout link to the human, then poll check_limits. It clearly states what the agent cannot do (complete payment) and names the follow-up tool. This is strong contextual routing.

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