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

Annotations already cover read-only/idempotent/open-world safety, but the description goes further with real operational facts: 15-minute result caching, a 1-request cost per completed search including cache hits, free failed searches, and the 200-vs-40 row page cap. Those are the kinds of billing and caching traits an agent cannot get from the annotations, though return-shape/pagination-truncation behavior is still unstated.

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?

Three sentences, front-loaded with the core action and scope, then operational facts, then the docs URL. No filler, and each clause carries information an agent can act on.

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 12 params at full schema coverage and no output schema, the description supplies the missing non-parameter context (cost model, caching, page size, docs link). What it omits -- the shape of a returned listing row and multi-page traversal behavior -- is minor but nonzero given there is no output schema.

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 the baseline is 3. The description still adds decision-relevant meaning beyond the schema by tying count to page yield ("up to 200 rows with count=200, or 40 without it") and noting a search costs one request at any size, which informs page-size choice rather than just restating the enum.

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 precise verb+resource+scope: "Search one page of eBay active listings by keyword" across a named set of marketplaces and sort orders. The word "active" cleanly separates it from the sibling ebay_sold tool, so an agent can route between them without opening either schema.

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?

Gives useful operating context (one page at a time, page size cap, cached results) but never names an alternative or a condition that selects one. It never says when to prefer ebay_sold or a marketplace-specific sibling, so routing still has to be inferred from the name.

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