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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so safety is covered. The description still adds real value beyond that: the exact computed formula, the non-inferred scope boundaries, a versioned dataset, and a direct REST fallback with a warning not to guess other /api/* paths.

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?

Well front-loaded: usage, exclusions, computation, inputs, output, formula, fallback, docs. It is somewhat padded by three near-identical example user requests and a formula line that restates the obvious, but nothing is actively misleading.

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?

With an output schema present the description need not explain return values, yet it still lists output fields, adds scope caveats, a fallback endpoint and documentation links. An agent has everything needed to invoke this correctly; the field list is mildly redundant against the output schema.

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 all four parameters have their own descriptions and defaults, so the schema carries the load. The description only restates the input names and types plus a full JSON example, adding no semantic detail beyond what the schema already provides.

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 ('Counts authority-scope working and non-working dates in a range') scoped to Saudi Arabia, and names the example scenarios it covers. It does not name which sibling (add_sa_working_days, check_sa_working_day, count_global_working_days) handles the excluded cases, so sibling differentiation is only partial.

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 an explicit when-to-use ('auditable Saudi Arabia working-day count', return the calculation rather than answering from memory) and a when-not-to-use list of excluded scopes (MHRSD leave, RTGS intervals, Umm al-Qura forecasts). It never routes the agent to the specific alternative tool for those cases, which keeps it below a 5.

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