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

Annotations already indicate readOnlyHint, openWorldHint, and idempotentHint. The description adds context: the API source (GSI), that no authentication is required, and the specific address format constraint. This goes beyond what annotations provide, though it could mention response format or rate limits for full transparency.

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 compact (two sentences plus a Japanese translation and a bold emphasis). It front-loads the core action and constraints, with no wasted words. Every sentence serves a purpose.

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 the tool has an output schema (not shown but indicated) and annotations covering safety/idempotency, the description provides enough context: API source, input format exclusivity, and usage directive. No further information is needed for an agent to select and invoke this tool 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?

With 100% schema coverage, the parameter `q` is documented in the schema. The description adds value by reinforcing the address-only constraint, providing an example, and warning against landmarks/station names. This clarifies usage beyond the schema's description.

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 clearly states the tool geocodes a Japanese address to latitude/longitude via the GSI AddressSearch API. It specifies the input format (address only, not landmarks/station names) and distinguishes itself from sibling tools like reverse geocoding or general geocoding by being Japan-specific and address-format-only.

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 provides explicit guidance: 'Call this for real coordinates of a Japanese address — do not estimate lat/lng from memory.' It also notes what inputs are unsupported (landmark/station names). However, it does not mention alternative tools for those unsupported cases, leaving the agent to infer that other geocoders might handle landmarks.

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