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

Annotations only cover the read-only/idempotent safety profile, and the description adds substantial behavior beyond that: the exact conversion algorithm, hemisphere handling of the equation of time, defaults for earlyLateZi, rejection of nonexistent local times, the needs_input fallback, and the supported date window. That is exactly the kind of context annotations cannot carry.

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?

Front-loaded with the primary action and the correction pipeline, and most sentences carry distinct constraints (ambiguity, defaults, date range, return contents). The bilingual restatement of the date range and the slightly cryptic 'Longitude and birth date are unchanged' sentence are minor waste.

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 9 parameters, a nested object and no output schema, the description does its job by summarizing returns (minute-resolution solar time, historical zone/offset, DST and Zi-hour policy) and the needs_input path. The gap is that boundaryChoices (DAY/HOUR/TERM) and when a boundary situation arises are never explained, so an agent facing that response has little to act on.

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 coverage is already 89%, so the baseline is 3; the description still adds meaning by tying repeated clock times to an explicit occurrence (daylightSaving), explaining that earlyLateZi defaults to false with a 23:00 day change, and noting that missing boundary choices produce needs_input. It leaves the DAY/HOUR/TERM boundary concepts themselves unexplained, which keeps it below 5.

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 verb and resource: convert historical local wall-clock time to true solar time, and enumerates the correction chain (DST removal, longitude correction, equation of time). It also carves out its own scope against siblings by declaring 'No pillars or lunar date are returned', which separates it from bazi_chart/qimen_chart.

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?

Gives clear operational context: repeated clock times need an explicit occurrence, nonexistent times are rejected, missing boundary choices return needs_input, and the Gregorian range is 1801-2099. It does not explicitly name an alternative tool or say 'use bazi_chart instead when you also need pillars', so it stops short of full routing guidance.

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