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

Annotations already cover read-only, idempotent, and non-destructive behavior. The description adds useful context beyond those: the exact scope (all 58 offices), filter behavior, 'no auth required', and the data source (JMA area constants, Japanese Government open data). This is solid but not exhaustive (e.g., no mention of rate limits or error cases), so a 4 is appropriate.

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?

The description is three dense sentences with zero filler: core function, return scope, consumer tools, filtering guidance, concrete examples, data source, and auth status. The essential information is front-loaded, and every clause 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?

For a simple one-optional-parameter reference tool with a full output schema and safety annotations, the description is complete. It tells the agent when to use it, what it returns, how to filter, example codes, and that no auth is needed. Nothing essential is missing for correct invocation.

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% — the name_filter parameter is already well-documented in the schema with case-insensitivity and examples. The description reinforces this with 'tokyo'/'osaka' examples and the purpose 'to find the right code', which adds marginal value but does not substantially exceed what the schema already provides. Baseline 3 is warranted.

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 opens with a clear verb-resource pair: 'Get the complete list of JMA forecast area codes with Japanese and English names.' It further specifies it returns all 58 offices/regions with 6-digit codes, and explicitly names the consumer tools, distinguishing it from weather forecast/overview/warnings siblings.

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 explicitly states the codes are 'needed by' three named sibling tools, making the use case unambiguous: fetch this reference before invoking weather forecast/overview/warnings. It also instructs how to filter ('Filter by English name keyword... to find the right code'), covering both when and how to use it.

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