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

With no annotations, the description carries the full burden. It discloses the PRO+ subscription requirement and the 403 response for lower tiers, which is useful. It also states the return format. However, it does not mention read-only nature, pagination, or other error behaviors, leaving gaps.

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 distinct sections for requirements, args, and returns. It is reasonably compact, though the Args block repeats schema descriptions, which is redundant but not overly verbose.

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?

The description covers access requirements, all parameters, and return fields, which is fairly complete for a data retrieval tool. It does not explain date parameter interactions or field meanings like 'bp' or 'adj_circle', but output schema likely covers those. Given the output schema exists, this level of description is adequate.

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. The description duplicates the schema's parameter descriptions without adding examples, constraints, or interaction semantics among start_date, end_date, and pub_date. It adds no value beyond 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 clearly indicates it provides basic information on indices tracked by ETFs, distinguishing it from sibling tools like index_daily or index_weight. However, it uses a noun phrase rather than an explicit action verb like 'get' or 'list', which slightly reduces clarity.

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?

No guidance is given about when to use this tool versus alternatives. The only note is the PRO+ subscription requirement and 403 error, which is an access restriction, not usage guidance. No exclusions or alternative tool recommendations are provided.

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