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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered. The description adds genuinely useful behavioral detail beyond that: Sunday-to-Monday substitution rules are applied and once-off declared holidays such as election days are included, which tells the agent what to expect in the payload. It stops short of stating coverage limits for historical or future years.

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?

One sentence, front-loaded with the resource and scope, with the qualifying detail about substitutions appended where it belongs. No filler.

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 no output schema, the description must convey what comes back, and it does so at a high level: holidays for the year including substitution dates and once-off declarations. It leaves the exact return shape (names, dates, whether substitution provenance is flagged) unspecified, which is a minor gap for a tool this simple.

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?

There is a single parameter with 100% schema description coverage, so the schema already carries the burden. The description only repeats the 'for a year' framing and adds no format constraints or valid-range guidance beyond the schema's 'e.g. 2026'.

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 ('Lists South African public holidays') plus the scope ('for a year'), which is unambiguous. It does not name or contrast itself against siblings like business_days_between, though their functions are distinct enough that confusion is unlikely.

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?

Usage is only implied: an agent infers this is the tool to call when it needs the holiday calendar, likely as input to business_days_between. There is no explicit when-to-use statement, no mention of alternatives, and no note on which years are supported.

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