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

With no annotations provided, the description carries the full behavioral burden and does so well. It discloses the 60 calls/min per client limit, that TARGET includes weekend closures, that IE and UK calendars list holidays only, that IE weekend substitution days are not modelled, and what each mode returns.

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 front-loaded with the core question and then packs scope, invocation modes, calendar limitations, and rate limit into a few dense sentences. Every sentence contributes information an agent needs before calling the tool.

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 three-parameter tool with no output schema or annotations, it explains both return modes, the calendar options, and important calendar edge cases. The only notable gap is the absence of guidance on what happens if neither date nor year is supplied, or if both are supplied.

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 baseline would be 3, but the description adds meaningful semantics: date drives a closed true/false answer with reason, year drives a list of closures, and the calendar parameter maps to target, ie, uk-ew, uk-sco, or uk-ni. It does not explain what happens if both date and year are omitted.

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 the exact decision the tool supports: whether a named payment rail is closed on a date, or which days it is closed in a year. It also names the supported calendars (TARGET, Ireland, UK variants), so an agent can immediately tell this apart from unrelated siblings such as check_regulator or stablecoin_rails.

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 tells the agent how to use the two modes: provide date=YYYY-MM-DD for a true/false closure result with reason, or year=YYYY for a list of closures. It does not name a competing sibling or an explicit when-not-to-use condition, but no sibling tool overlaps this calendar-checking purpose.

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