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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so safety and determinism are covered. The description adds genuinely new context: the chart is derived from Gregorian input and the palace interpretations are 'rule-based', which sets expectations that the reading is deterministic rather than free-form analysis.

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 sentences: the first front-loads what is built and what comes back, the second gives the trigger. The component enumeration is long but earns its place because there is no output schema, so the agent needs to know what the payload contains.

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 5 parameters, no output schema, and a fairly complex domain (astrological computation), the description covers the essentials: inputs, computation basis, and returned structure. The only residual gap is the undocumented optional 'name' field, which affects nothing about invocation correctness.

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 80%, so the schema already documents gender, view_year, birth_date and birth_time, and the description mainly restates them as the inputs. It adds no format or edge-case meaning, and the lone undocumented parameter (name) is left unexplained in both places. Baseline 3 applies when the schema carries the load.

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 and resource — 'Builds a Vietnamese Tử Vi Đẩu Số (Purple Star) birth chart' — and then enumerates the computed components (lunar date, can chi, nạp âm, cục, 12 palaces with stars, per-palace reading). That output list makes it unambiguously distinct from siblings like convert_lunar_solar, which only converts dates.

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?

It gives an explicit trigger: 'Use when the user wants their Tử Vi chart or asks what their chart says.' That is clear context for selection, but it names no exclusion or alternative (e.g., when to use convert_lunar_solar instead), so it falls short of the 5-level routing clarity.

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