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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint=false and destructiveHint=false, so the description earns extra credit by adding facts not in annotations: determinism and hard limits (64 KB input, 1 s per call, 1 MB result). No contradiction with the declared safety profile.

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 purpose, then When / Not for / Side effects / Deterministic / Limits in scannable order. Slightly over-long because the Spanish text is followed by an English restatement that ends in a dangling artifact ('[EN completo / full EN: inputSchema.description]'), which is noise rather than 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?

With an output schema present the description needn't explain return values, and annotations cover the safety profile; the description fills the remaining gaps (determinism, size/time limits, sibling routing). Nothing an agent needs in order to call it 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 adds real meaning by framing the two parameters as two conversion directions ('o viceversa'). It stops short of stating the operating rule the empty required list leaves open — that exactly one of datetime or julian_date should be supplied.

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 first sentence states a concrete bidirectional verb+resource: convert UTC date-time to Julian Date/MJD/Julian Day Number or back. It is instantly distinguishable from siblings such as timestamp-convert or date-iso-week, and it names the resource precisely.

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 'Cuándo' section gives the triggering condition (calendar/timezone results that must be exact: offsets, DST, month ends, leap years) and 'No para' names the concrete alternative (sun-times). This is exactly the when/when-not/alternative structure.

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