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

The description reveals several non-obvious behaviors beyond the read-only/idempotent annotations: the 366-day maximum, Europe/Rome default, resolution of movable annual dates, and exclusion of expired recurrences. These details meaningfully help an agent understand what will happen when invoking the tool.

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?

Three short sentences, each carrying distinct value: operation scope, default behavior, and recurrence handling. No redundant wording, and the most important information is front-loaded.

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?

The description covers core date semantics and recurrence behavior, while the output schema and annotations fill in return-shape and safety details. It is slightly short on explicit alternative-tool guidance and timezone interpretation for user-supplied dates, but it remains adequate for correct invocation.

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?

With 50% schema description coverage, the description compensates for date parameters by adding the inclusive-range cap and the timezone default. The schema already documents topic, start_date, end_date, authority_status, and limit/offset constraints, so the combination is sufficient.

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 uses a specific verb and resource: 'List days on a date or in an inclusive date range', with an explicit maximum range of 366 days. It is clear and unambiguous, but it does not explicitly contrast with sibling tools such as search, fetch, or list_topics, so it stops short of full sibling differentiation.

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?

The first sentence states the exact use case—listing days for a date or date range—and the default timezone clarifies behavior when dates are omitted. It does not explicitly list when-not-to-use or point to alternatives, but the context is clear enough for an agent to know when this tool applies.

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