buy_it_now

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

The description discloses a key behavioral trait: 'Proceeds to checkout — final payment must be completed on eBay.' This goes beyond the schema by explaining the workflow and that payment is not handled by the tool. However, it does not mention potential side effects like an irreversible purchase, authentication requirements beyond the passed credentials, or error conditions. With no annotations, more transparency could be provided.

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 concise and efficient, consisting of two sentences. The first sentence states the primary action, and the second clarifies the checkout flow. There is no redundant information or awkward phrasing, and the key details are front-loaded.

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?

The description covers the core action and the checkout handoff, but it lacks details on expected return values, success/failure behavior, or prerequisites (e.g., item must have Buy It Now available). Given that there is no output schema, the agent is left without guidance on what the tool returns. This gap makes the description incomplete for a transactional tool.

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?

The input schema has 100% coverage of parameter descriptions, so the baseline is 3. The description adds no additional explanation of parameters such as quantity or username, relying entirely on the schema. It doesn't clarify how credentials are used or what quantity default means beyond the schema.

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: 'Purchase an eBay item immediately using Buy It Now.' It specifies the verb, resource, and method, distinguishing it from sibling tools like place_bid which would be for auctions. The additional note about proceeding to checkout further clarifies the purchase flow.

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 implies usage for immediate purchases via Buy It Now, but it does not explicitly mention when not to use it or provide alternatives. Siblings like place_bid exist, but there is no direct comparison or exclusion statement, leaving the agent to infer the distinction.

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