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

With no annotations, the description carries the behavioral burden and does well: it discloses the data source (Cabinet Office), timezone (JST), date constraint, and bank-calendar semantics. It stops short of stating the exact return value or behavior for out-of-range dates, but the check semantics are mostly inferable.

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 a single front-loaded sentence that wastes no words: it leads with free status, states the core check, then gives the boundary condition and alternatives. Every clause adds decision-relevant information.

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 two-parameter boolean check with no output schema, the description covers scope, data source, calendar variants, and sibling routing. It is slightly incomplete only in not explicitly stating the return type or error/out-of-range behavior, but an agent has enough 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 coverage is 100%, so the schema already documents the date format and the national/bank enum. The description adds beyond the schema by clarifying that the free check is limited to today through 90 days ahead in JST, and that bank mode adds Dec 31-Jan 3 holidays.

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 verb and resource: 'check whether a date ... is a business day in Japan.' It adds clear scope ('between today and 90 days ahead (JST)') and distinguishes this free tool from paid tools for other dates, making its role among siblings clear.

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 says when to use the tool: free checks within the 90-day JST window, and 'For other dates, business-day arithmetic or holiday lists use the paid tools.' This gives agents a direct routing rule for choosing between this tool and its siblings.

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