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

With no annotations, the description must carry the whole behavioral load. It does disclose the important trait — this is an async, two-phase flow returning order_id and payment_url, with crypto payable from an agent wallet — which is real value. However, for a monetary mutation it says nothing about irreversibility, cancellation, or what happens if the listing is already sold or payment fails, which are the traits an agent most needs before spending funds.

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?

Three short sentences, front-loaded with the action and its return values, then the follow-up step. No filler, and the ordering matches how an agent needs the information.

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?

There is no output schema, and the description compensates by naming both returned fields and the required polling step. Auth is covered by the schema's api_key note. Only the failure/irreversibility angle is absent, which keeps it short of a 5.

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 the schema already explains id, coupon, method, and api_key, and the baseline applies. The description's only added parameter context is that crypto can be paid by an agent wallet, a marginal but genuine clarification of the method enum.

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 ("Start buying a listing") plus the marketplace scope, and names the outcome (order_id, payment_url). An agent can distinguish this from get_listing (browse) and create_listing (sell) without opening any 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?

Gives the follow-up path explicitly: after buying, poll get_order for delivery. That's an actionable usage rule, and the method enum (crypto/card) tells the agent which channels exist. It stops short of stating when NOT to use it (e.g., already-sold listings or when the buyer lacks balance), so it's clear context but not full when/when-not guidance.

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