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

Annotations already declare a safe, idempotent, closed-world read, and the description adds substantial context beyond that: the exact calendar scope (2026 statutory/public-office only), what is not inferred, the counting formula, the full output field set including substitute_day_policy and dataset_version, and a specific REST fallback endpoint with a warning not to guess other paths. This is genuinely additive behavioral disclosure.

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?

The description is long but well-structured with labeled sections (usage, when-not, what it computes, inputs, outputs, formula, REST fallback, docs) and front-loads the use case. Listing all the output fields is slightly redundant given a declared output schema, but nearly every line carries usable information.

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?

Given a 4-parameter tool with 100% schema coverage, full annotations, and a declared output schema, the description supplies everything an agent needs: usage conditions, exclusions, input example, calculation formula, and a fallback endpoint plus docs link. Nothing required to call it correctly is missing.

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 parameter names with types and optionality and gives a complete JSON example, but adds no format or edge-case semantics beyond what the schema already documents (e.g. nothing about inclusive-range defaults or validation errors).

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: 'Counts authority-scope working and non-working dates in a range', plus a concrete label ('auditable South Korea working-day count'). It is clear what the tool does, but it never names the sibling alternatives (check_kr_working_day for single dates, add_kr_working_days for date shifting), so it does not explicitly differentiate itself from the surrounding family.

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?

Provides an explicit when-to-use ('when you need an auditable South Korea working-day count') and an explicit when-not-to-use (the package covers only the 2026 statutory/public-office schedule; private-employer, school, bank, exchange, local-government and 2027 schedules are not inferred). It also instructs the agent to call it directly rather than answering from memory. It stops short of routing to any named alternative tool.

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