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

Annotations cover the safety profile (readOnlyHint=true, openWorldHint=true), so the bar is lower, and the description adds real operational context beyond them: the data source (KASI special-day list) and the per-call cost/payment mechanism ($0.005 USDC via x402 on Base). No disclosure of latency, caching, or rate limits, but pricing is a notable, non-obvious trait.

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?

Front-loads the core question, then adds returned fields and the payment note in two short sentences with no filler. Slightly more than minimal but each clause carries 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?

No output schema exists, so the description usefully enumerates what is returned, and the payment model is disclosed. The remaining gap is the undocumented date format, which an agent must guess at call time.

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?

There is a single required 'date' parameter with 0% schema description coverage, and the description says nothing about its expected format (ISO 8601? YYYY-MM-DD?) or timezone handling. With structured data providing no semantics, the description should compensate and does not.

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?

States a specific verb+resource ('Is a date a Korean business day?') and further specifies the returned content (weekday, weekend flag, official Korean public holiday names including substitute/temporary holidays). This clearly separates it from siblings like kr_business_day_add and kr_business_days_count, which manipulate rather than test a single date.

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 phrasing implies a single-date lookup, and the sibling set (kr_business_day_add, kr_business_days_count, kr_business_status) makes the distinction inferable, but the description never states when to prefer this over those alternatives or any prerequisites. Usage is implied rather than stated.

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