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

Annotations only declare readOnlyHint and openWorldHint; the description adds substantive behavior beyond that — the 25-item cap, spec ordering (card_specs first), group-row id substitution with resolved_groups reporting each substitution, and a commission disclosure field accompanying buy_url links. It stops short of stating what happens with unknown or partially-resolvable ids, which is the one behavior an agent would still have to guess.

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 headline ('Full detail for up to 25 products') followed by a dense enumeration of returned fields. It is long but nearly every clause adds information; only the disclosure sentence could be tightened without loss.

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 full burden of describing the response and does so thoroughly: spec ordering, ratings with evidence quotes, all offers with price and buy_url, attribute_provenance, resolved_groups, and the disclosure field. For a read-only, two-parameter tool this is enough for an agent to call it and interpret the result.

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 50% — user_signature is fully documented in-schema while ids is a bare string array. The description compensates by explaining that ids accepts both product ids and shelf row ids and how group-row ids resolve to top_pick_id, which is genuine meaning beyond the schema's maxItems: 25.

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 with scope: 'Full detail for up to 25 products', then enumerates exactly what detail is returned (specs, ratings, offers, provenance). It contrasts implicitly with summary-style siblings like search_products, but never names lookup_product or search_products to make the boundary explicit.

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 implied rather than stated: an agent infers this is the detail-expansion step after obtaining ids from search or browse. There is no explicit 'use this instead of lookup_product when...' or any guidance on when to prefer the single-product sibling over this batch call.

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