lookup_branch

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

With no annotations, the description carries the full burden. It discloses that branch data is lazily fetched from the public zengin-code dataset and cached locally, providing important context about network dependency and potential staleness. This exceeds what the schema/annotations provide.

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 sentences, front-loaded with the action and resource. The additional sentence about lazy fetching and caching is valuable and does not waste space.

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 tool with a simple input schema and an output schema present, the description covers the purpose, input formats, data source, and caching behavior. No critical gaps are evident for the tool's complexity.

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?

The schema provides no descriptions (0% coverage), but the description compensates by specifying that bank_code is a 4-digit bank code and branch_code is a 3-digit branch code (支店コード). This adds concrete format meaning beyond the schema's empty strings.

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 uses the specific verb 'Look up' with a clear resource ('bank branch') and explicitly defines the required identifiers (4-digit bank code + 3-digit branch code). This distinguishes it from sibling tools like lookup_bank, which operates at the bank level.

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 usage for branch lookup by stating the exact input formats, but it does not provide explicit guidance on when to choose this over sibling tools like lookup_bank or search_banks. No exclusions or alternatives are mentioned.

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