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

Annotations already declare readOnly/idempotent/non-destructive/openWorld=false, and the description still adds real substance: a deterministic guarantee, the exact coverage window (2026-2029), the Friday-Saturday weekend policy, a formula, the precise REST fallback endpoint with a warning not to guess other paths, and a docs URL. Coverage limits (what is 'not inferred') are disclosed rather than hidden.

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?

It is long but well labeled and front-loaded: use-trigger first, then what-it-computes, inputs, outputs, formula, fallback, docs. Some waste exists in triplicated examples (three 'user requests', three JSON argument examples, plus schema examples), and the ambiguous 'Do not use this when' line costs clarity.

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 the enumerated Outputs list is largely redundant, but the description still supplies everything an agent needs: coverage window, weekend policy, jurisdiction boundary, fallback endpoint, and documentation. The main gap is the confusingly worded exclusion clause, which could leave an agent unsure how MHRSD/RTGS/government cases relate to this tool.

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 coverage is 100% and the single date parameter is already documented (Gregorian, Saudi coverage, format date), so the description adds little beyond restating the input name and repeating example values already present in the schema. Baseline 3 is appropriate when the schema does the heavy lifting.

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?

It states a specific verb and resource (check a date against the Saudi working-day calendar) and pins the scope to SAMA/financial-institution calendars with an explicit Friday-Saturday baseline and 2026-2029 window. It does not name the sibling check_sa_working_days / add_sa_working_days / count_sa_working_days tools, so the distinction from related SA tools is left implicit. The 'Do not use this when financial-institution scope only' sentence is garbled and muddies the boundary it tries to draw.

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 a clear use trigger ('when you need a deterministic ... result'), an instruction to call directly rather than derive from memory, and a when-not list covering other Saudi leave/holiday domains. The exclusions are not mapped to named alternative tools, and the one malformed exclusion sentence weakens otherwise strong routing guidance.

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