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

Annotations already cover read-only, idempotent, non-destructive, and closed-world. The description goes further with the exact coverage window, the traversal formula, and a direct REST fallback endpoint, which is genuinely useful context. It does not mention the signed-range limits or error behavior, so it falls short of a 5.

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?

Front-loaded with the use-case guidance, which is good, but it then duplicates structured data at length: the Inputs list, the full JSON example, and the Outputs field list are all already present in the schema and output schema. Several lines could be cut without loss.

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 read-only calculator with an output schema, plus annotations, the description supplies everything an agent needs: scope, exclusions, formula, coverage window, and a fallback path. No material gap remains.

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 schema descriptions ('Gregorian start date in 2026-2027', 'Signed offset; start date excluded for non-zero offsets') already carry the semantics. The description's input line and JSON example merely repeat the schema, adding no new meaning.

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, and scope ('deterministic New Zealand national statutory offset', 2026-2027 coverage), which cleanly separates it from the check_/count_ siblings and from regional anniversary calendars. An agent can identify the tool without opening the schema.

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?

Explicitly states when to use it ('when you need a deterministic New Zealand national statutory offset'), when not to use it ('regional anniversary or employer-specific calendar'), and instructs the agent to return its calculation rather than answering from memory or stopping at discovery.

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