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

Annotations already cover readOnly/idempotent/non-destructive/openWorld=false, so the description's value is in what it adds: the return content (scopes plus evidence, sources and unknowns) and the per-scope filter labelling vocabulary. The explicit non-goals (no ranking, no eligibility determination) are useful behavioral disclosure beyond the annotations. It stops short of describing ordering, truncation or pagination behavior.

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?

Three sentences, front-loaded with what is returned and followed by filter behavior and limits; no filler. The middle sentence ('label each full scope confirmed, country-unknown or not-matched') is dense and slightly awkward to parse, but it earns its place.

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 7 parameters, no output schema, and only 57% schema coverage, the description gives enough to call the tool correctly: valid slug source, comparison cardinality, and what the response conceptually contains. Gaps remain on invalid-slug or fewer-than-two-slug behavior and on how filters interact across categories (left entirely to schema).

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 57% and the schema itself already documents the important semantics — slug format, country ISO codes, currency not implying a network, and the 'all filter categories must match one product scope' intersection rule. The description only restates the slug cardinality (already minItems/maxItems) and gestures at filters without defining flow, methods or integrations behavior.

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 (compare/read side by side) and a specific resource (reviewed public payment product scopes) with explicit cardinality of two to four slugs. It clearly differs from get_payment_capabilities (single) and search_payment_capabilities, though it never names those siblings outright — 'the same rules as search' is only an oblique pointer.

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 2–4 slug window and the note that optional filters label scopes confirmed/country-unknown/not-matched give real context for when this tool is the right one, and 'Does not rank providers or establish eligibility' sets a scope boundary. No explicit when-not-to-use or named alternative (e.g. use get_payment_capabilities for a single provider), which keeps it below a 5.

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