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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, and the description still adds value beyond them: determinism guarantee, no stored state, and concrete operational limits (64 KB input, 1 s per call, 1 MB result) that no annotation encodes. It also discloses the subtle month-step clamping behavior, which is the kind of trait that would otherwise cause wrong calls.

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?

Content is front-loaded and the When/Not-for/Side-effects/Limits labels are scannable, but the payload is duplicated wholesale in Spanish and English and ends with a dangling artifact ('[EN completo / full EN: inputSchema.description]'). The redundancy costs tokens without adding information.

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?

An output schema exists so return values need no explanation; the description covers purpose, exclusions, determinism, side effects, limits, and the non-obvious clamping rule. Nothing an agent needs to invoke this correctly is missing.

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%, so the baseline is 3; the description earns above that by clarifying semantics the schema only hints at, such as month steps clamping to month end and the 1,000-date ceiling interacting with step size. It does not, however, explain the skip_weekends interaction with step/unit or give format examples, so it stops short of 5.

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 dates from start to end, inclusive') plus the scope qualifiers that matter: step unit, month-end clamping, 1,000-date cap, optional weekend skipping. It also names the sibling it is not (date-between), so an agent can distinguish it without opening either 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?

Explicit 'When' clause ties usage to exact calendar/time-zone results (DST, leap years, offsets, month ends), and an explicit 'Not for' clause routes difference computations to date-between. Both the use case and the exclusion are stated, not implied.

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