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

Goes well beyond the readOnly/idempotent/openWorld annotations: it discloses the exact computation rule ('move one day at a time; decrement only on status.is_working_day=true'), the precise coverage boundary (substitute dates, regional/sector/employer/school/bank schedules excluded), and a direct REST fallback endpoint with a warning not to guess other paths.

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?

Front-loaded with the usage directive, which is good, but the block is long and choppy: it enumerates an Outputs field list that duplicates the output schema, and repeats input names already in the schema. Several fragments (example user requests, formula, fallback, docs) pad the body without adding selection value.

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 calculation tool this covers everything an agent needs: when to use, when not to, inputs, computation rule, edge-case scope, and a REST fallback. With an output schema present, the description needn't explain return values further.

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 parameters are already documented in the schema, including the 'start date excluded for non-zero offsets' caveat. The description restates the inputs and adds a JSON example, which is helpful but redundant with schema examples, 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?

States a specific verb and resource with scope: 'Adds or subtracts Belgium authority-scope working days in exact coverage.' An agent can distinguish this from check_be_working_day and count_be_working_days without opening a schema, and the region-of-scope qualifier is explicit.

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 an explicit trigger ('Use this when you need a deterministic Belgium working-day offset') and a genuine exclusion ('Do not use this when private-sector statutory core only... not inferred'), plus instructs to call directly rather than answer from memory. It never names the sibling alternatives (check_be_working_day, count_be_working_days) that an agent should pick when it wants a boolean check or a range count, so it stops short of full routing guidance.

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