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

Annotations only declare readOnly/openWorld/non-destructive; the description adds real behavioral context beyond them — the no-exact-match fallback where eBay serves loosely related listings flagged by `exactMatches: false` plus a `notice`, and the billing model (one unit per result page fetched). The only weakness is that the cost warning references `max_results`, which is not a parameter name in 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 purpose and return fields, then filters, then caveats — a sensible ordering with little waste. It loses a point for redundancy: "Returns JSON" is stated at the start and again as a standalone sentence, and the field enumeration partially repeats the filter list.

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 13-parameter scraper with no output schema, the description covers what is returned, how to filter/sort/page, the marketplace-currency implication, the misleading-results fallback, and the cost profile. An agent has everything needed to call it correctly and interpret edge-case responses.

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 adds modest value by grouping the filters and noting that price filters are in the marketplace's currency and that marketplaces differ in price/availability, but it introduces no parameter meaning the schema does not already carry.

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?

Opens with a specific verb + resource + scope ("Searches any regional eBay marketplace for `keyword` and returns the listings as JSON") and then enumerates the exact return fields, which separates it cleanly from siblings like amazon_search, google_shopping and google_search without requiring the agent to open a 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 concrete operational guidance: which parameters filter, which sort, how to page (with the allowed 60/120/240 sizes), and that `marketplace` should be set when site-specific prices/currency matter. It never states when not to use it or names an alternative tool (e.g. google_shopping or amazon_search), so it stops short of full alternative routing.

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