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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false, and openWorldHint=false, so the safety profile and the absence of network access are covered. The description adds the substantive points that the data is a fixed, approximate, city-centre-only table and what to do when a city is missing. The instruction not to call external services largely repeats openWorldHint=false, which keeps this from a 5.

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 scope statement and the fallback instruction come first, and every sentence carries information. The full Chinese and English duplication doubles the length without adding content, which is the main inefficiency.

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 no output schema, the description still conveys the data's nature, precision, and limits well enough to use it correctly. It does not say how results are keyed (city names in Chinese or English, list vs. mapping), which is the one gap an agent might hit.

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?

The tool takes zero parameters, so the baseline is 4. The description correctly implies no input is needed and instead specifies the acceptable numeric range for data the agent must obtain from the user.

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 names a specific verb and resource: returning a built-in table of approximate city-centre longitudes for Chinese cities. It also sets a clear boundary ("只是市中心近似值…Not a gazetteer"), which tells an agent exactly what class of tool this is and is not.

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 states the use case (confirming the location used for chart casting or the user's birthplace), the fallback when the place is absent (ask the user for a number between 73 and 135.5), and two explicit prohibitions (do not guess, do not call an external geography service). Little is left to inference.

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