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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds genuine value beyond that by specifying which derived facts come back (Tam Tai, Kim Lâu, palace for men and women) and by fixing the target year as 2027, which is not encoded in the schema.

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 dense sentence, front-loaded with the verb and target year, with no filler. The enumeration is long but each item is load-bearing given there is no output schema.

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 responsibly lists the returned facts, and the annotations cover safety and determinism. What remains unstated is minor: whether results are fixed for 2027 only and whether any input validation beyond the schema range is enforced.

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?

Only one parameter exists and schema coverage is 100%, with the schema already stating the Gregorian birth year and the 1920–2100 bounds. The description's phrase 'for a birth year in the lunar year 2027' confirms the interpretation but adds no format or edge-case detail beyond the schema, so the baseline 3 applies.

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 gives a specific verb ('Returns') and a precise resource: the traditional facts for a birth year in lunar year 2027 (Đinh Mùi). Enumerating the returned fields (age, branch/stem relation, element relation, Tam Tai, Kim Lâu, yearly palace) makes it easy to distinguish from siblings like create_tuvi_chart or find_compatible_birth_years, though it never names those alternatives explicitly.

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?

Usage is only implied: an agent can infer you call this when a user asks about a birth year's 2027 outlook. There is no explicit when-to-use, when-not-to-use, or pointer to a sibling for related questions such as compatibility or chart creation.

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