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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the bar is lower; the description still adds real context beyond them: it is rule-based with no live fetch, its knowledge cutoff is stated, and the response shape (verdict, urgency enum, doNow/dont, modifiers, sources) is spelled out. The 'always relay official instructions' caveat is a useful behavioral disclosure.

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?

Purpose is front-loaded in the first clause, but the body is one enormous sentence enumerating every alert type, level name, colour and renamed category. Much of that inventory is genuinely useful coverage, yet the density hurts scannability and the return-value list could be tightened.

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 and does so: it enumerates the input forms accepted, the rule sources and cutoff, the full response structure, and the urgency taxonomy. An agent has everything needed 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 description coverage is 100%, so all four parameters are already documented, including the lang enum and the alert-id source URL. The description reinforces that text may be Japanese or English and that an alert id can substitute, but adds no new semantics and never mentions the 'situation' parameter. 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 and resource ('Decode the text of a Japanese emergency alert ... or an alert id') and immediately scopes the rule sources (JMA / Cabinet Office / J-ALERT / MoE as of 2026-10-17). No sibling tool overlaps, and the title plus first sentence make the domain unmistakable.

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?

Gives a clear trigger ('Give text or alert') and an explicit exclusion via 'No live data: it explains the alert the user already has', plus 'call this instead of guessing' when training data predates the 2026 renaming. It never names a concrete alternative tool, so it stops short of the 5 bar, but the when/when-not boundary is unambiguous.

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