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

Annotations already cover the safety profile (readOnly, openWorld, non-destructive), so credit goes to the added context: a concrete cost model ('5 prepaid credits per successful call') and a disclosure that MCP returns only a 'compact view' of results. The mention of 'item URLs' as an input path not present in the schema is a minor inconsistency that could mislead.

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 resource and return fields, which is good, but the single run-on sentence mixes purpose, return shape, use cases, pricing and an MCP caveat. The 'eBay search or item URLs' clause is noise that does not correspond to any actual parameter.

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 usefully enumerates returned fields and qualifies them with 'when available'. Cost per call and the compact-view caveat are exactly the kind of context an agent needs before committing credits. Pagination and the misleading item-URL capability are the remaining gaps.

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 explains query, domain enum and results limit. The description adds no parameter-level detail such as query syntax, marketplace-specific behavior, or result caps. Baseline 3 applies; the 'item URLs' phrasing arguably misdescribes the input surface.

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 ('eBay product search and item data API') and enumerates the returned fields (titles, prices, condition, shipping, links). It is clearly distinguishable from siblings like search_amazon, search_walmart and search_shopping by naming the marketplace. The 'item URLs' claim is muddled since the schema exposes only a query string, but the core purpose is unambiguous.

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?

'Supports marketplace research and price comparison' implies usage but never states when to pick this over search_shopping or search_amazon, nor any exclusions. An agent must infer that the eBay-specific marketplace is the differentiator. Adequate but with a clear routing gap.

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