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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world, so the safety profile is covered. The description adds genuinely useful behavior beyond that: the ranking is rule-based (Vietnamese day-selection), personalization is optional, and the response mixes recommended days with reasons, auspicious hours, and days to avoid.

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?

A single front-loaded sentence that leads with the verb and scope and ends with the return shape. The parenthetical activity list (wedding, opening a shop, moving house…) duplicates the enum values already documented in the schema and could be trimmed.

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 correctly carries the burden of describing the return value (best days, reasons, good hours, days to avoid) and covers both required and optional inputs. It is only slightly thin on ordering/ranking format details, but nothing critical for a correct call 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 description coverage is 100%, including enum labels for all ten activities and the bride/groom roles for the birth-year fields, so the schema does most of the work. The description only adds the high-level notion that birth years are optional and apply to the people involved, which is largely already conveyed in the schema.

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 ("Ranks the days of one Gregorian month") plus the rule system used (Vietnamese day-selection rules) and what the output contains (best days with reasons and good hours, days to avoid). That is clearly distinct from siblings like convert_lunar_solar or create_tuvi_chart, which do conversion and charting rather than day ranking.

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?

Gives clear context for when the optional personalization applies (birth years of the people involved, with the schema noting the bride/groom case for weddings). It does not name an alternative tool or state exclusions, but the sibling set contains no direct competitor for day selection, so the omission is minor.

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