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

With readOnlyHint=true and destructiveHint=false in annotations, the description still adds meaningful behavioral context: positions include 'degree ranges rather than only sector names,' with the reason for that choice. It also exposes a non-obvious timing rule—'All four move at Li Chun in early February, not at Lunar New Year'—and states that the changeover date is returned. This is substantial value beyond the annotations.

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?

Four sentences with the core result front-loaded in the first sentence. Each subsequent sentence earns its place: the degree-range rationale, the Li Chun vs Lunar New Year clarification, and the intended use cases. No filler or repetition of schema fields.

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?

For a read-only lookup with one required parameter and no output schema, the description covers the four returned afflictions, the positional format, and the calendar boundary—enough to invoke correctly. The exact response object shape and field names are left implicit, which is a minor gap given the tool has no output schema to fill it.

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 description carries no obligation to document parameters. It does reinforce the 'solar year' and Li Chun boundary, but that mirrors what the schema already says for the year parameter. The baseline 3 is appropriate because the description adds no new parameter-level meaning.

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 opens with a specific verb-object statement: 'Return the four annual feng shui afflictions for a solar year with their exact positions,' then enumerates Tai Sui, Sui Po, the Three Killings, and the Five Yellow. The title and content clearly separate this from the flying-stars and bagua sibling tools. No ambiguity about what resource this tool addresses.

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 context for when to use the tool: 'Built for renovation planning, date selection and yearly guidance features.' It does not explicitly name alternatives or state when not to use it, but the intended application is clear enough for an agent to make a reasonable selection decision.

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