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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is well covered. The description adds useful context about chart content and foundational role, but it does not disclose operational behaviors such as how unknown birth time is handled, timezone assumptions, or how lunar/legacy parameters affect computation. With annotations present, this is an acceptable but not rich disclosure.

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?

The description is three sentences with no filler. The first sentence front-loads the chart contents, the second establishes its role relative to other tools, and the third gives concrete usage examples. Every sentence earns its place and the structure is easy to scan.

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?

Given the tool's complexity (15 parameters) but the presence of a rich input schema and an output schema, the description does not need to restate parameter details or return values. It provides the key contextual signals an agent needs for selection: what the chart contains, that it is foundational, and example user phrasings. A small gap is the lack of any hint about when not to use this tool or which sibling addresses more specialized chart-reading tasks.

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%, so the schema already documents every parameter. The description adds no parameter-level meaning beyond what the schema provides. Per the baseline rule, a 3 is appropriate when the schema carries the full semantic burden.

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 clearly explains that the tool produces a Four Pillars natal chart and enumerates the chart components (stems/branches, Ten Gods, hidden stems, five-element ratios, Spirit Stars, Twelve Life Stages). It does not use a direct verb like 'calculate' or 'generate', and it does not explicitly contrast itself with any sibling tool, though labeling it 'the foundation other tools build on' provides some positional clarity.

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 gives explicit user-intent examples ('show my saju / bazi chart', '내 사주 봐줘'), which tells an agent when to invoke this tool. It also states that it is the foundation for other tools, implying it is the right first step for chart-related requests. It does not enumerate exclusions or alternative tool conditions, so it stops short of a 5.

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