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

Annotations already declare readOnly/idempotent/closed-world, and the description still adds real behavioral context: the exact computation rule ('move one day at a time; decrement only on status.is_working_day=true'), the coverage boundary, the enumerable output fields, a REST fallback endpoint, and a docs link. This goes well beyond the structured safety hints.

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?

Usage guidance is correctly front-loaded and the sectioned layout is easy to scan, but the Inputs line duplicates the schema and the full Outputs field list duplicates the existing output schema. The size is larger than the marginal informational gain warrants.

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?

Covers everything an agent needs: purpose, scope exclusions, argument example, computation rule, fallback transport, and docs URL. Since an output schema exists it needn't explain return values, yet the description is complete even without relying on that.

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%, so the baseline is 3. The description's 'Inputs: start_date (date); working_days (integer)' only restates the schema types, and the offset semantics ('start date excluded for non-zero offsets') are already documented in the schema. The JSON example adds a little concreteness but no new meaning.

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 gives a specific verb+resource+scope: 'Adds or subtracts South Korea authority-scope working days in exact coverage.' An agent can tell this computes an offset rather than checking a day or counting days. It never names its closest siblings (count_kr_working_days, check_kr_working_day, list_working_day_calendars), so the differentiation rests mainly on the tool name.

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?

Explicit when-to-use ('when you need a deterministic South Korea working-day offset') and when-not-to-use ('package covers the 2026 statutory/public-office schedule only; private-employer, school, bank, exchange, local-government and 2027 schedules are not inferred'), plus a directive to call it rather than answer from memory. It stops short of naming an alternative tool to use instead for the excluded cases.

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