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

With no annotations, the description carries the burden, and it does disclose two useful traits: the call is free and returns 'current' (not historical) data. It omits whether the tool is read-only (strongly implied by 'warnings'), the response shape, and any failure behavior for unknown prefectures.

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?

One sentence, front-loaded with the key differentiator ('FREE') and immediately followed by what the tool returns and the accepted input forms. Nothing is wasted.

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?

Given a one-param, no-annotation, no-output-schema tool, the description covers the essential facts: cost, currency of data, accepted input forms, and default. Return-value structure is the only material omission, and it is minor for a simple list endpoint.

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 0% for the single optional parameter, but the description compensates well by stating it accepts either a prefecture name or an office code, and by giving the default value (Tokyo / 130000) with a concrete example code format.

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 names a specific resource (current JMA weather warnings) and its scoping input, which is clear enough to distinguish from a raw feed. It never names or contrasts the siblings raw_warning or watchlist, so an agent must infer the boundary itself.

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?

There is no guidance on when to choose this over raw_warning or watchlist, nor any stated preconditions. The only selection hint is the word 'FREE', which implies a cost trade-off but doesn't route the agent explicitly.

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