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

Adds substantial behavior beyond the annotations: the call charges nothing, a 24-hour Stripe Checkout link is issued for agent-created accounts vs the billing page for a person's account, and the human must never be asked for card details. It also restates idempotency in operational terms ('the same idempotency_key returns the same link'), which concretizes the idempotentHint annotation rather than merely echoing it.

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, all front-loaded with the primary purpose and trigger first, and each earns its place except the 'human_message' instruction, which references a field the caller cannot see in the schema. Minor loss for that dangling reference.

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 an output schema present, return values need no explanation, and the description covers safety, cost, timing, and account-type branching well. The one gap is the unexplained 'human_message' hand-off: it is central to how the link reaches the human, yet it is absent from the schema and undefined in the description.

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%, so usd and idempotency_key are already documented, and the description adds only the idempotency-retry behavior already implied by the annotation. More concerning, it instructs 'Send human_message unchanged,' but no such parameter exists in the schema, which muddies rather than clarifies parameter 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?

States a specific verb and resource ('Get a payment link ... to add prepaid credits to this account') and immediately resolves the mismatch between the name add_credits and the actual behavior (returns a link, does not itself add credits). An agent can distinguish it from get_balance and the other siblings without opening 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 trigger conditions are given: 'Use when get_balance is low or a call failed for insufficient credits,' plus the follow-up step 'Check get_balance after they pay.' It names the sibling to consult both before and after, leaving nothing to inference.

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