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

Annotations only declare readOnlyHint=false and destructiveHint=false; the description goes well past that with commercial consequences an agent could not otherwise know: one-time payment, no refund on being outbid, current $51 minimum, and an always-dofollow link. That is precisely the kind of irreversible-cost disclosure a caller needs before invoking.

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?

Five short sentences, front-loaded with what the tool gets you, then cost, then prerequisite. Every clause carries a fact an agent needs; nothing is padded or repeated.

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 simple two-parameter transactional tool with no output schema, the description covers effect, price, refund policy, and precondition. It leaves open what a successful bid returns (current price, position, next minimum), which matters in a competitive auction, but no output schema exists to backfill that.

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 both parameters are already documented, and the description's "Omit amount_usd to bid $51" merely restates the schema's "Omit to bid the minimum (51)." No syntax, increment, or range detail is added beyond the schema, so the baseline 3 applies.

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 verb+resource pair ("bid" + "Featured spot") is explicit, and "It sits above every listing" pins down exactly what the placement is. It cleanly separates itself in spirit from the read-only sibling read_featured, though it never names that sibling.

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 prerequisite "The product must already be listed" gives a concrete precondition that determines whether the call is legal, and the $51 minimum sets the bidding context. It stops short of naming alternatives such as read_featured or x402_bid_featured, so there is no explicit when-not or sibling routing.

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