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

readOnlyHint=true already tells the agent this is a safe read, so the description only needs to add behavior beyond that. It does add two useful facts: results are ordered by total count descending, and the counting criteria stay consistent with the list view. It says nothing about pagination, whether cities with zero parks appear, or what happens on an invalid enum value.

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 compact sentences, front-loaded with what is returned and its sort order, followed by the filter caveat. No filler, no restatement of the tool name, and every clause carries information an agent would otherwise have to guess.

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 one-optional-parameter aggregate with no output schema, the description covers the metric set, the ordering, and the filter semantics. It could be marginally stronger by describing the returned city key or how unknown cities are handled, but nothing essential for correct invocation is missing.

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 enum and its single-line description are already documented. The description still adds value beyond the schema by making explicit that omitting benefitType means all parks are counted, and that the filtered counting matches the list view's criteria. That default-state and consistency information is not present in the schema.

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 aggregation: per-city park totals plus the count already operating, sorted descending by total. That is a distinct verb+resource combination that separates it from sibling detail tools like list_parks and get_park. It stops short of naming those siblings explicitly, so differentiation is inferred rather than stated.

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?

"宏观选址用" signals the intended scenario (macro-level site selection), which implies the agent should reach for this when it wants aggregated comparison rather than individual park records. However, no alternative tool is named and no when-not-to-use condition is given, so the routing decision is left partly to inference.

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