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

With no annotations provided, the description carries the burden of behavioral disclosure. It reveals the access restriction (PRO required, 403 otherwise), the matching behavior (exact symbol match), and the return format (JSON array with specific fields). However, it does not disclose pagination, data freshness, or rate limits, which are common behavioral aspects for data APIs.

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 well-structured with clear Args and Returns sections, and the access requirement is front-loaded. It is concise and free of irrelevant details. A slight deduction because the parameter descriptions duplicate the schema, but overall it's efficient and organized.

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?

Given there is no output schema provided, the description includes return fields, which is helpful. It covers the access restriction and parameter meanings. However, it lacks usage context relative to sibling tools and does not mention potential error cases (beyond the 403) or edge cases like empty results. For a simple data retrieval tool, it is adequate but not fully complete.

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 description coverage is 100%, with each parameter already described (e.g., symbol, start_date, end_date, ann_date). The description's Args section largely duplicates these schema details, adding no new meaning beyond what the schema already provides. It does not clarify optionality or interplay between parameters, so the baseline of 3 is appropriate.

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 clearly indicates the tool returns ETF net asset value data ('ETF 净值'), and the return fields (unit_nav, accum_nav, etc.) reinforce this. However, it does not explicitly differentiate this from sibling tools like etf_daily or etf_adj_factor, so it misses the sibling distinction that would elevate it to a 5.

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 mentions the PRO requirement and 403 error for lower tiers, which is a prerequisite, but it provides no guidance on when to use this tool versus alternatives like etf_daily or index_daily. There is no 'when to use' or 'when not to use' advice, so usage guidance is effectively absent beyond the access restriction.

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