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

Annotations already declare readOnly/idempotent/openWorld, and the description goes well beyond them: 15-minute result cache, one request charged per completed search including cache hits, failed searches free, ~50 rows per page, and that prices are seller asks rather than transaction prices. Cost and caching semantics are exactly the kind of behavior an agent cannot infer from structured 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?

Four short sentences with zero filler, and the most important framing (what is searched, geographic scoping, no sold data) is front-loaded ahead of billing and caching notes. Every sentence carries distinct, actionable information.

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 an 18-parameter, high-complexity tool with no output schema, the description covers result size, pricing semantics, caching, and cost, which is most of what an agent needs. It leaves pagination/cursor usage entirely to the schema, which is acceptable but means the description does not fully stand on its own for multi-page retrieval.

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 schema already documents all 18 parameters in detail (radius fallback behavior, cursor chaining, sort enum limits, etc.). The description only restates that the search centers on a ZIP or point, adding no new syntax or format guidance beyond what the schema provides; baseline 3 is appropriate.

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 (Search) and resource (OfferUp US active listings) with scope qualifiers: one page, near a ZIP code or point, about 50 rows. It also explicitly excludes sold search, which matters because sibling tools like ebay_sold and mercari_sold exist. An agent can distinguish this from offerup_item (single item) and the *_sold siblings on name+description alone.

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 clear context (active listings near a location, not sold data) and a useful exclusion ("No sold search"), so the agent knows this is a live-listing search. It does not, however, point to a specific alternative or spell out when a different search tool (eBay, Mercari, etc.) would be preferred; the routing is implied by the OfferUp name rather than stated.

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