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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered. The description adds real behavioral context beyond that: the coverage scope ('authority-scope', exact coverage), the caveats about which closures are NOT inferred, and the step-by-step formula (move one day at a time, decrement only on is_working_day=true). It does not, however, detail date-range limits or rate/error behavior.

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?

It is front-loaded with the usage decision and scope caveats, which is the right ordering. It is somewhat long: the full output-field list, formula, REST fallback and docs URL add bulk, though each serves a purpose. Overall efficient but not maximally tight.

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?

With an output schema present, enumerating return fields in the description is partly redundant, but coverage, formula, inputs, and a runnable JSON example make the definition self-sufficient for a country-scoped calculator among many siblings. Minor redundancy keeps it from a 5.

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 both params (start_date, working_days) are already documented, including the signed-offset and start-date-exclusion semantics. The description's 'Inputs' line merely repeats the parameter names and adds no syntax or meaning beyond the schema. Baseline 3 is appropriate.

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 states a specific verb+resource+scope: adding/subtracting Finland authority-scope working days. It explicitly frames the tool as a deterministic offset computation and distinguishes it from the discovery/legacy path ('call this tool directly... instead of ... stopping at discovery').

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 gives explicit when-to-use ('when you need a deterministic Finland working-day offset') and when-not-to-use conditions (nationwide public-holiday-only layer, Midsummer Eve, Christmas Eve, employer/collective-agreement/sector/school/bank/Åland/Sámi and local closures not inferred, private-sector leave treatment). It also directs the agent to return the calculation rather than answer from memory.

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