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

Goes well beyond the readOnly/idempotent/openWorld annotations: it discloses the 5-minute bid-result cache and, crucially, tells the agent to treat a cached bid as a lower bound near auction close. It also notes that shipping is calculated to a destination country and prices come back in the site currency — real behavioral context an agent could not infer from the schema.

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?

Front-loaded with the operation and return fields, then the ID sourcing, then the cache caveat last — a sensible ordering. Every sentence carries information the agent needs; the cache/lower-bound warning is long but is the single most important operational detail.

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?

With no output schema, the description compensates by enumerating returned fields (title, description, seller, price, bid count, quantity, condition, times, shipping), which is sufficient. It lacks any mention of error behavior for an invalid or removed ListingID, which is the one remaining gap for a lookup-by-ID 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?

Schema description coverage is 100%, so all four parameters (including the enum of country sites, _apiKey, and ship_to) are already documented in the schema. The description adds only the sourcing hint for listing_id ('from ebid_search results or an ebid.net listing URL') and the generic mention of destination-country shipping, so 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?

States a specific verb and resource ('Fetch one eBid.net listing by its numeric ListingID') and enumerates the returned fields, so the agent knows exactly what it gets back. It names the underlying API operation (GetListingSingle) and is clearly distinct from the sibling ebid_search (many results) and ebid_listing_bids.

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?

Explicitly routes the agent to ebid_search to obtain ListingIDs and confirms it works for both live and ended listings on any country site. It does not mention the sibling ebid_listing_bids, which is the natural alternative when the agent actually wants bid history, so one routing decision is left implicit.

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