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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the safety profile is covered. The description does add genuine behavioral context beyond that: the Saturday-Sunday baseline convention, the Act's Sunday substitution rule being preserved with no Saturday-to-Monday substitution inferred, and the Idd-ul-Fitr/Idd-ul-Adha dates being pinned to the 2026 Gazette (so future lunar dates need a refreshed package). However, that content is embedded in a wall of caveats and partly restates the output field list, so it lands at a solid 3 rather than higher.

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?

This is a long description, but nearly every sentence carries a distinct obligation: when to use, when not to use, the roster convention, the gazette pinning caveat, the substitution rule, the computed output, an example, inputs, a JSON sample, output fields, the formula, and the REST fallback. It is front-loaded with the routing decision and structured with clear labelled sections.

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 date-range calculator with a fully described schema and an output schema, the description supplies everything an agent needs: the calculation convention, jurisdiction caveats, lunar-date limitations, an input example, the formula and a REST fallback URL with a warning not to guess other paths.

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% and every parameter carries its own description plus examples, so the schema does the heavy lifting. The description's 'Inputs:' line and complete JSON example mostly restate what the schema already shows, adding no syntax or edge-case detail beyond it. Baseline 3 is appropriate.

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?

The description states a specific verb and resource ('Counts authority-scope working and non-working dates in a range') and frames the tool as a Kenya-specific working-day counter, which separates it from the check_/add_ siblings. It does not explicitly contrast itself with check_ke_working_day or add_ke_working_days, leaving sibling differentiation to inference.

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?

Explicit direction to 'Call this tool directly and return its calculation instead of answering the formula from memory,' followed by a clear 'Do not use this when...' clause scoping out private-employer, bank, school, county, sector, diplomatic and shift-work calendars. Both the when and the when-not are spelled out.

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