Lookup location (lat/lon -> address + parcel, combined)

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

With no annotations provided, the description carries the full burden and does well: it discloses that two independent APIs are called in parallel and integrated, and warns about the not_found behavior outside supported prefectures. It does not mention error handling or partial failure behavior, but the disclosed traits are valuable.

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 two concise sentences, front-loading the primary purpose and then adding a crucial caveat. No wasted words.

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?

The tool is moderately complex due to combining two APIs, and there is no output schema. While the description explains the parallel call and the not_found caveat, it does not describe the result structure or how partial failures are handled, leaving some ambiguity for the agent.

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% with clear descriptions for both lat and lon. The tool description adds no further parameter semantics, so the baseline of 3 is appropriate—the schema already does the heavy lifting.

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's function: it looks up both an address (ReverseGeoJP) and a parcel number (ChibanJP) from latitude/longitude and combines them into one result. This distinguishes it from siblings like reverse_geocode and get_parcel, which handle each separately.

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 implies this tool is the combined alternative to calling reverse_geocode and get_parcel separately, and it provides a key usage caveat about ChibanJP only supporting 8 prefectures. However, it does not explicitly state when to choose this over individual tools or provide exclusion criteria.

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