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

Annotations only cover the safety profile (readOnly, idempotent, closed-world), and the description adds substantially beyond that: a tri-state is_holiday (true/false/null) tied to a `covered` flag, a `matches` list because a movable feast and a dated holiday can coincide, and a martial-law caveat where ст. 73 is suspended. Without an output schema, this is exactly the kind of return-value semantics the agent needs.

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 answer is front-loaded in the first line, and the follow-on paragraphs each address a distinct return-value nuance rather than padding. It is dense with backticked field names but no sentence is redundant; the martial-law note could arguably be tightened.

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 one-parameter lookup with no output schema, the description covers the two things that would otherwise be guesses: the null-versus-false distinction and the shape of `matches`. An agent can call it and interpret the response without further documentation.

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 100% and the single `date` parameter is documented as ISO YYYY-MM-DD in the schema itself. The description adds no format, range, or timezone detail beyond that, so the baseline 3 applies.

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 sentence gives a specific verb-and-resource pairing: decide whether a given date is a public holiday or non-working day in Ukraine. No sibling tool covers holiday calendars, so there is no ambiguity to resolve, and an agent can select this tool from the name plus first line alone.

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 supplies clear usage context by framing the tool around deadline calculations and by warning that null must not be read as 'no'. It does not state any when-not conditions or name alternatives, but no sibling overlaps this domain, so the practical gap is small.

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