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

Annotations already declare readOnlyHint=true, openWorldHint=true, idempotentHint=true, and destructiveHint=false, covering safety and mutability. The description adds that data comes from MLIT's library and implies it returns a list, but doesn't disclose details like pagination or rate limits. Given the strong annotation coverage, the description adds modest value, so a 3 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?

Two sentences, front-loaded with purpose and source, followed by a usage directive and example. No redundant phrases or unnecessary details. Every word earns its place, making it highly concise and well-structured.

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 list tool with full schema coverage, annotations for safety, and no output schema, the description covers purpose, usage, parameter format, and an example. It explains why an agent would call it and what it returns. There are no missing pieces needed to invoke it correctly.

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 both parameters are documented. The description adds meaning beyond the schema by explaining the prefecture parameter accepts either a name or code (though the schema also says that) and by giving a concrete example of the code format (13102). It also clarifies that _apiKey is optional and that a shared key is used otherwise, which is not in the schema. This adds practical value.

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 action ('List'), a clear resource ('cities/wards and their 5-digit municipality codes within a Japanese prefecture'), and names the source (MLIT's 不動産情報ライブラリ). It also gives a concrete example (Chuo-ku, Tokyo = 13102) and explicitly ties the tool to resolving codes for realestate_transactions, distinguishing it from the sibling tool. This is a precise, unambiguous purpose.

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?

The description explicitly says 'Use to resolve a city code for realestate_transactions' and provides a usage example. It names the sibling tool (realestate_transactions) and gives the condition for use, which is more than enough to route an agent correctly. While it doesn't list 'when not to use', the example and purpose make the intended usage clear.

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