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

Annotations already declare readOnly/idempotent/openWorld=false, so the safety profile is covered; the description adds real value on top with a deterministic guarantee, the exact step algorithm ('decrement only on is_working_day=true'), the 2026-2027 coverage boundary, and a REST fallback path. It stops short of stating rate limits, error behavior, or what happens for out-of-window dates.

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 and chunked into labeled sections (Use when / Do not use / What it computes / Inputs / Outputs / Formula / REST / Docs), so an agent can scan for routing cues fast. Slightly over-long because enumerating all fourteen output fields duplicates the existing output schema, which is the only real padding.

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 two-parameter deterministic calculator with an output schema present, the description covers triggers, exclusions, coverage window, algorithm, argument example, and a fallback endpoint. Return values are already in the output schema, so the long Outputs list is unnecessary rather than missing. Nothing essential to a correct call is absent.

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 schema already documents start_date (Gregorian, 2026-2027) and working_days (signed, start date excluded). The description's Inputs line and JSON example merely restate them; the formula adds slight interpretation of how the offset is applied but no new syntax or boundary meaning. 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?

States a specific verb+resource (adds/subtracts South Africa national working days) and pins the scope to exact 2026-2027 national public-holiday coverage. The 'What it computes' line plus the explicit exclusion of employer-specific/non-national schedules cleanly separates it from the ~60 sibling country tools and from add_sa_working_days/check_south_africa_working_day.

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?

Opens with a direct 'Use this when...' trigger and follows with an explicit 'Do not use this when you need an employer-specific exchanged holiday or non-national schedule' exclusion. It further instructs the agent to call the tool rather than answer from memory, which is exactly the routing behavior the sibling set needs.

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