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 genuinely useful behavioral context beyond that: the calendar authority scope, that Bangkok-only and Islamic-bank/southern-branch conditions remain explicit and are not generalized, and that substitute-day policy is surfaced. It stops short of rate limits or 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?

Front-loaded with the usage directive, but the body is cluttered: a pseudo-formula, a full REST fallback with URL, and a docs link sit alongside the core description. The output-field list duplicates an output schema that already exists. Useful content, but not tightly sized.

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 4-parameter, output-schema-backed tool this covers scope, inputs, an argument example, and fallback invocation, so an agent can call it correctly. Listing all output fields is redundant given the output schema, but nothing essential is missing except explicit sibling routing.

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% with defaults and examples already documented, so the schema carries the parameter burden. The description restates inputs with types and one complete JSON argument example, which is mildly helpful but adds no semantics beyond the schema. 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 (count Thailand working days) and immediately scopes it as a Bank of Thailand financial-institution calendar, explicitly not a universal Thai employee/government calendar. That scope statement is exactly the axis that separates it from the many sibling count_*_working_days and add_th_working_days tools.

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?

Gives explicit usage instructions ('call this tool directly and return its calculation instead of answering from memory') and an explicit exclusion ('Do not use this when this is a Bank of Thailand financial-institution calendar...'). It never names a sibling alternative by name, so 5 is not warranted, but the when/when-not framing is clear.

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