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

Annotations already mark it read-only/open-world, and the description adds genuinely non-obvious context: the version history is this service's own record (MHLW keeps none), removals are dated, and no reason is inferred for a removal. That framing prevents an agent from misreading removal entries as enforcement actions.

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?

Four dense sentences with the core scope front-loaded and the caveats (own record, free window, no inferred reasons) placed after. No sentence is filler, though the list of change kinds and the filter mention are slightly redundant with schema/enum.

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 annotations and an output schema present, the description supplies the behavioral framing an agent needs: data provenance, removal dating, window limit, and the absence of inferred reasons. Only an explicit sibling comparison is missing.

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 100%, so the schema already documents `since`, `limit`, `prefecture` and `change_type` with formats and enum values. The description only names the two optional filters, adding little syntax or semantics beyond the schema, so 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?

The description states a specific verb and resource: which institutions were added/modified/removed/reappeared on MHLW's foreign-patient hospital list. The change-feed framing implicitly separates it from the static lookup sibling, though no sibling is named explicitly.

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?

It establishes clear usage terms: a required `since` date, optional prefecture and change_type filters, and a free window of the last 30 days. It doesn't explicitly say to use foreign_patient_hospital_lookup for current state instead, but the change-oriented scope makes the alternative inferable.

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