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

Annotations already declare readOnly, idempotent, and non-destructive behavior. The description adds valuable context beyond that: the data source is Sina and keyless, it returns closing levels and daily change, and each index includes specific fields such as open, day high/low, and 52-week high/low. It does not discuss rate limits or staleness, but for a keyless read-only snapshot this is adequate.

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 description is front-loaded with the core purpose and then compactly enumerates indices, example queries, return fields, and source. Every sentence adds useful information; the bilingual examples are helpful without being bloated.

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 fully covers the return value contract by listing the indices and the per-index fields. It also names the data source and confirms no key is required, making the tool self-contained enough for an agent to call it correctly with no further context.

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 has zero parameters and the input schema is empty, so the description carries no parameter documentation burden. The baseline for zero-parameter tools is 4, and the description further compensates by explaining exactly what data the tool returns, which is more useful than any parameter documentation would be.

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: a Hong Kong stock market snapshot covering the full Hang Seng index family, and it enumerates every index included. It clearly distinguishes this tool from quote-style tools by emphasizing the index family scope and closing-level summary data.

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?

The description provides concrete example queries in both English and Chinese, making it clear when an agent should invoke this tool. It does not explicitly name alternatives or exclusions, such as when to use hk_quote instead, but the use context is clearly implied by the query examples and index-family scope.

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