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

Annotations cover the safety profile (readOnly, idempotent, non-destructive), and the description adds substantial context beyond them: the exact formula, the limitation that schedule-dependent substitute days remain unresolved, the enumerated output fields, and a REST fallback path plus docs URL. This is unusually rich disclosure for a read-only calculator.

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-loads the when-to-use condition, then segments inputs, outputs, formula, and fallback with clear labels. Slightly long because it restates outputs already covered by the output schema, but every block is scannable and purposeful.

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 2-param read-only calculator with annotations and an output schema, the description covers scope, exclusions, formula, and fallback endpoint completely. Nothing an agent needs to invoke it correctly is missing, and the redundant output listing is harmless rather than a gap.

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 two parameters (start_date, working_days) are already fully documented including the signed-offset and start-date-exclusion semantics, so the description's 'Inputs' line largely repeats structured data. The complete JSON argument example adds marginal value, but the baseline 3 applies when the schema carries the 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?

States a specific verb (adds/subtracts) and resource (Canada federal working days) and immediately distinguishes scope: 'federally regulated-employer calendar' versus provincial/private-employer/schedule-specific. An agent can separate it from add_us_federal_working_days or the provincial siblings without opening schemas.

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?

Explicitly gives when-to-use ('deterministic baseline offset for a federally regulated-employer calendar, 2026-2027') and when-not-to-use ('provincial, private-employer or schedule-specific substitution result'), plus the instruction to call it directly rather than answering from memory. Nothing is left to inference.

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