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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint, so the safety profile is covered. The description usefully adds that related offers and the seller's other listings are optionally bundled, but says nothing about auth requirements, rate limits, or what happens when a slug is missing/invalid.

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?

Two tight sentences with the identifying verb/resource and the slug selector front-loaded, followed by the return payload. No filler, no repetition of the title, no wasted clauses.

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 carries the burden of describing the return payload and does so by enumerating the field groups returned. It is nearly complete for a read tool whose annotations already cover safety; only edge-case behavior (invalid slug, truncation interaction) is unaddressed.

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 all three parameters (slug, includeRelated, maxDescriptionChars) are already self-documenting. The description echoes slug and the optional-related behavior but adds no syntax, format, or default guidance 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?

States a specific verb (get) and resource (marketplace listing details) and enumerates the fields returned — price, condition, shipping, compatibility, seller, photos, links. The singular 'by slug' implicitly separates it from the search-oriented sibling search_marketplace_listings, but no sibling is named outright.

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?

Usage is only implied: the schema says the slug comes 'from search results', which suggests you call this after a search, but the description itself gives no when-to-use, when-not-to-use, or alternative-tool guidance versus get_marketplace_seller or search_marketplace_listings.

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