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

The annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so safety is covered. The description adds genuinely non-derivable semantics: null means 'not published by the facility / 要問合せ' and never 0 — a critical distinction for interpreting fees and hours that appears nowhere in the structured fields.

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?

A single sentence, front-loaded with the scope, that packs the return-field inventory and the null-vs-zero rule with zero redundant wording. Every clause carries information an agent would otherwise have to guess.

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 compensates by enumerating the returned fields and explaining the null sentinel. For a one-parameter read tool whose annotations already declare safety, nothing an agent needs to call it correctly or interpret the result 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 description coverage is 100% and the sole parameter's provenance (from search_facilities or search) is fully documented in the schema. The description adds no further format, validation, or failure semantics for slug, 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?

Names a specific resource (one facility) and enumerates exactly what it returns: hours, pickup schools, fees with conditions, source URL, verification date, application page. That is far more than a restatement of the name. It stops short of a 5 because it never names the sibling it complements (search_facilities), leaving the routing to the slug parameter's schema note.

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 single required slug, documented in the schema as coming from search_facilities or search, signals this is the follow-up detail call after a search. There is no explicit when-to-use/when-not and no statement about what happens if the slug is unknown.

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