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

Annotations only say it is a non-readonly, non-idempotent, open-world call; the description adds the important detail that this only produces a PayPal checkout link and nothing is charged until user approval, plus the listing lockout. That is real value beyond annotations. It omits link expiry, behavior if already paid, and why the call is non-idempotent.

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?

Front-loaded verb phrase followed by WHEN, actor, return, and consequence in a compact sequence — every sentence carries information. The closing usage example is the weakest element, since it shows an empty argument object that conflicts with the listing_id the operation implies.

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 two-parameter, no-output-schema mutation, the description covers what is returned (PayPal checkout link), what is not done (no immediate charge), and the downstream state change (cannot list again). Remaining gaps are edge cases such as already-paid or expired-link behavior, which are secondary.

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 schema already documents both key and listing_id, and the description adds nothing about their format or semantics. The trailing "Example: barter_pay_cut {}" suggests an empty call despite listing_id being described as the agreed listing id, which mildly muddies rather than clarifies parameter use. Baseline 3 applies.

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?

Specific verb+resource: "Pay house cut" plus the qualifier that it returns a PayPal checkout link for exactly the house cut amount. It scopes the operation ("Seller only", "cash deal"), which separates it from the crypto payment sibling without naming it. Naming the alternative (e.g. plan_pay_crypto) would earn a 5.

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 WHEN clause: a cash deal is agreed with both sides confirmed and the house cut is due, and it states the actor restriction (seller only). It also gives the blocking consequence (cannot list again until paid), which tells the agent why to call it now. It does not explicitly exclude a crypto-path alternative, so the agent must infer routing.

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