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

The description goes far beyond the annotations by disclosing the cost model (10% only on sale, nothing per view), the self-pausing behavior, the monthly cap semantics, the absence of bidding, the relevance-gate requirement, the exact refusal codes, and the meaning of `status` values. This is unusually complete behavioral disclosure for a mutating tool.

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 long but dense with operational necessity: purpose, cost, constraints, refusals, and response semantics are all covered. It is front-loaded by stating the action and scope first. It loses a point for being a single wall of text with no structural breaks, which makes parsing heavier than it needs to be.

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 paid mutation with no output schema, this description is nearly complete. It explains prerequisites, exact failure modes and how to resolve them, retry/idempotency behavior, post-call status values, and what the reply contains. An agent has enough information to decide, invoke, and interpret the result without guessing.

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 67%, and the description compensates for the undocumented `listing_id` by adding ownership, active-listing, network, and review-eligibility constraints. It also enriches `monthly_cap_usdc` by explaining that `0` immediately leaves the slot and that a higher cap only raises the ceiling. It adds little to `idempotency_key`, but the schema already documents that parameter well.

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 opens with a specific verb and resource: 'Buy the promoted slot for one of your listings.' It also clearly distinguishes this tool's scope by saying the promotion appears only in `search`, not in `ask`, previews, webhooks, the job board, or the website. This makes the purpose unmistakable and separates it from related listing/search siblings.

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 gives clear invocation conditions: only the owner may call it, an API key is required, credit must exist, the listing must be active, and the network must be supported. It even maps refusal codes to remediation steps, such as 'buy credit first' for `no_credit`. It does not explicitly name a sibling alternative, but the promotion action is unique and the guidance is otherwise strong.

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