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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds real behavioral context beyond that: authority-scope limits, government-office-only fuel-conservation entries cancelled April 8, no inference of private employers/essential services, and the explicit one-day-at-a-time algorithm. The garbled do-not-use sentence costs it a point.

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?

Badly bloated and poorly front-loaded: it dumps the full output field list despite an output schema existing, includes a REST fallback URL and docs link, and buries the actual purpose among contradictory caveat sentences. Several sentences do not earn their place, and the 'Do not use this when...' construction is syntactically broken.

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?

An output schema exists, so enumerating return fields is unnecessary, but the description does fill the important gap of calendar-scope caveats (what is and is not inferred, dataset limitations). For a 2-param, richly annotated tool it is nearly complete, missing only clean routing against its country-sibling alternatives.

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 restates the two inputs and supplies a complete JSON argument example, but adds no semantics the schema lacks (signed offset, start-date exclusion, -1000..1000 range are all in the schema).

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: 'Adds or subtracts Sri Lanka authority-scope working days in exact coverage', plus the formula (move one day at a time, decrement only when status.is_working_day=true). This distinguishes an offset operation from the sibling check_lk_working_day/count_lk_working_days family, though it never names those alternatives directly.

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 opening line gives a use condition ('when you need a deterministic Sri Lanka working-day offset'), but the 'Do not use this when' clause is incoherent — it reads as a scope disclaimer ('this is a combined official holiday-class calendar, not a universal private-employer closure rule') rather than a genuine when-not/alternative routing statement. No sibling tool is named as an alternative.

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