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

Annotations already declare readOnlyHint=true and idempotentHint=true, so the safety profile is covered by structured data. The description adds genuine domain context (the two-pillar collapse, the year-pillar reading) but says nothing about the credit cost beyond the header note, and nothing about output shape.

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?

Two tight sentences that front-load the definition and then the disambiguation, plus a compact metadata footer for group and cost. No wasted text, though the cost/group lines are boilerplate rather than value.

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 not be explained, and the concept is well-defined. But for an 11-parameter tool with low schema coverage and a domain-specific concept, the description leaves too much about input handling and the year-vs-other-pillar choice unstated.

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 11 parameters at only 36% schema description coverage, the description must carry more of the load than it does. It adds nothing about date, time, timezone, or the fields/precision compact-mode behavior, yet the nà yīn result depends critically on how the birth data is 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?

States a specific concept ('the sound-element of each pillar') and pre-empts the most likely confusion by clarifying what it is NOT ('it is not the day master'), directly differentiating it from the sibling astroway_bazi_day_master. The sixty-jiazi-to-thirty-names mechanism makes the resource unambiguous.

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 description implicitly signals it answers the popular 'what is your element' question, but it never states when to call this vs. alternatives like bazi_day_master or bazi_element_balance. It distinguishes the concept but not the usage decision.

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