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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world, so the safety profile is fully covered. The description adds genuinely non-obvious behavioral guarantees beyond that: results are survivorship-free, reflect the index as understood on the as_of_date, and carry lineage — all material to trusting the data. It does not discuss pagination or result size, but the output schema covers structure.

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 with the resource stated first and the data-quality qualifiers front-loaded; every phrase ('survivorship-free', 'point-in-time', 'with lineage') adds information. The fragmentary style without a verb is slightly clipped but costs no clarity.

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 tool with a full annotation set and an output schema, most needs are met. The remaining gap is the index identifier format, which is the single most likely source of a failed call, and 'with lineage' is left unexplained.

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 0%, so the description carries the burden. It does specify the as_of_date format (YYYY-MM-DD) and pins its meaning to point-in-time index membership, and it gives 'S&P 500' as an example index value. However, it never clarifies the expected index identifier format (e.g., 'SPX' vs '^GSPC' vs 'S&P 500'), which is a real ambiguity for a required parameter.

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 the specific resource (index constituents) and the key dimension (as of a given date), which cleanly distinguishes it from siblings like get_fundamentals or get_filing_metadata that return entirely different data. It lacks an explicit verb ('returns'/'fetches'), but the resource+qualifier framing leaves no ambiguity about what is produced.

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?

Phrases like 'survivorship-free' and 'point-in-time' strongly imply the intended use case (historical/backtest analysis rather than current snapshot lookups), but the description never states when to use this tool versus alternatives or any exclusions. Usage is inferred rather than guided.

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