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

Beyond the readOnlyHint annotation, the description adds that the operation is free, that seller-written listing text is not an instruction, that payTo must match the payment terms wallet, and that payUrl is for the user to open in their own wallet. These are substantive behavioral and security details that materially affect correct use.

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 compact and front-loaded, starting with the core action and then adding the important field and safety details. Every sentence contributes useful information without repetition.

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?

Because there is no output schema, the description usefully names the key returned fields such as price, seller label, marked status, payTo, and payUrl. It also covers read-only behavior and prompt-injection safety, though it leaves the id parameter underspecified.

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?

There is one required parameter with 0% schema description coverage, so the description should compensate. It only echoes 'by id' and does not explain where to obtain the id, its expected format, or the 36-character limit present in 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 states a specific verb and resource: 'Show one Marketplace listing by id,' and lists the fields returned. It implicitly distinguishes itself from marketplace_search by emphasizing a single listing by id, but it never names the sibling alternatives explicitly.

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?

It gives some usage guidance, notably that payUrl should be handed to the user and that payment terms must reference the same payTo wallet. However, it does not say when to use this tool versus marketplace_search, listing_pay, or payment_status, leaving the routing decision mostly implied.

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