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

Annotations already declare read-only, idempotent, open-world behavior, and the description adds material context beyond them: a 15-minute cache TTL, the cost model (1 request per completed lookup including cache hits, failures free), and the semantic warning that status is seller-declared rather than a verified sale. This is exactly the operational detail an agent needs for budgeting and result interpretation.

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 core action and return contents, then billing/caching, then semantics and docs link — each sentence carries distinct information. Slight inefficiency: the cost sentence uses 'search' terminology for an item-fetch tool, which could momentarily confuse an agent.

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 competently enumerates returned fields and adds caching, cost, and status semantics, which is enough for correct invocation. Missing only explicit failure-mode behavior (e.g., what an invalid/expired ID returns) and rate-limit ceilings.

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 100% and the single q parameter is fully documented in the schema (listing ID, numeric item number, or offerup.com/item/detail/... URL). The description only echoes 'ID or URL' and adds no syntax or format detail 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?

"Fetch one OfferUp listing by ID or URL" names a specific verb and resource, and the enumeration (description, posted date, condition, coordinates, shipping, photos, seller and vehicle details) tells the agent exactly what detail is returned. The singular 'one listing' contrasts implicitly but clearly with the sibling offerup_listings search tool.

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 context for use: fetch a single listing by ID or URL obtained from search results, with the caveat that 'status is the seller-set state, not a verified sale.' It does not explicitly name offerup_listings as the alternative for browsing/discovery, so the routing is inferred rather than stated.

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