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

With no annotations, the description carries the full burden and does disclose the response content: a boolean plus the reason (holiday name, weekend) and half-day/early-close flags. It also states the important aggregation rule that a date is a business day only if open in every calendar given. It omits error behavior for unknown calendar codes and any timezone/date-boundary handling.

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 core question and the aggregation rule are front-loaded, and every sentence carries information. The dense run of four bracketed calendar examples in one sentence is useful but makes the description heavier than it needs to be.

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 tool with no output schema, the description covers inputs, semantics, and the shape of the answer (reason strings, half-day flags). A little more on the exact return fields or handling of invalid codes would make it complete.

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 description coverage is 0%, so the description must supply all meaning, and it does: calendars are calendar codes with real examples and AND-semantics across the list, and date is yyyy-mm-dd defaulting to today. The cross-calendar conjunction rule is genuinely new information not present anywhere in the schema.

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 opening question states a specific verb (check) and resource (business day) and immediately scopes it to one or several calendars. It is clearly distinguishable from siblings like business_days_between (a count) and add_business_days (a shift), since this returns a yes/no plus reasons.

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 calendar examples (USD.FX/EUR.FX for a EUR/USD trade, XNYS.SETTLE for NYSE settlement, TARGET2.PAY for euro payments, GBLON.BANK for London banks) give concrete selection guidance and point to list_calendars for codes. It stops short of explicitly saying when to prefer this over siblings such as business_days_between or market_status.

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