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

Annotations already declare readOnlyHint and idempotentHint, so the description wisely spends its words elsewhere: it discloses the closed built-in dataset, states that locale affects display only and not the match set, and forbids silent first-item selection. The only minor gap is that it does not describe ordering or size limits of the candidate list.

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 sentences are dense but front-loaded: purpose first, then disambiguation policy, then failure handling. The one waste is the enumeration of returned fields (name, district, level, lat/lon, IANA timezone, longitude range), which is redundant given an output schema exists.

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 two-parameter read-only lookup with an output schema, the description covers everything an agent needs: data provenance, display-vs-match semantics for locale, ambiguity policy, and a fallback path on no match. Nothing essential is deferred to the schema or left to inference.

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 100%, so the baseline is 3, but the description earns above baseline by clarifying that locale is presentational only and cannot narrow or widen results — a semantic an agent could easily get wrong from the schema alone. The city parameter's disambiguation hint is mostly duplicated from the schema, which keeps it from a 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?

The opening clause gives a specific verb and resource ('根据城市名返回城市信息候选') and bounds the data source ('内置表，不访问外链'), which no sibling tool description would match. It even enumerates the returned fields, so an agent knows exactly what kind of lookup this is before opening the schema.

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 prescribes concrete behavior for each outcome: a single candidate may be used directly, multiple candidates must be confirmed with the user and never silently truncated, and a miss requires asking for a nearby major city or user-supplied coordinates/timezone. These are explicit when/when-not rules rather than implied usage.

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