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

With no annotations, the description carries the full burden and does a good job: it discloses the paid gate ($0.01 USDC), the concrete failure mode (payment-required error until payment is attached to request _meta), and that settlement only occurs on success. It stops short of describing non-payment failure modes (e.g., not-found, missing fields).

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 core purpose is front-loaded in the first sentence, followed by payment mechanics in the order an agent needs them. It is dense but every sentence contributes a distinct fact; minor redundancy in restating the price twice ('$0.01 USDC' and 'the same price').

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 single-parameter read tool with no output schema or annotations, the description covers purpose, cost, failure mode, and an alternate invocation path. The main omission is any indication of the returned listing's shape, but 'full listing including contact details' gives a reasonable signal.

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 0% and there is one required parameter. The description references {listing_id} inside the HTTP URL template, confirming it is the listing identifier, but adds no format, constraints, or example values beyond that incidental mention.

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 ('Get one full listing including contact details'), which is clear on its own. It does not explicitly contrast itself with search_listings or publish_listing, though 'one full listing' implies by-ID retrieval versus search.

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 usefully explains an access-path alternative (plain HTTP with an x402 client) for callers lacking x402 support, which is real usage guidance. However, it never says when to choose this tool over search_listings or how a caller obtains a listing_id, leaving selection guidance implicit.

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