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

No annotations are provided, so the description must disclose behavioral traits. It says 'Retrieve' and mentions additions/removals, but it does not specify the response structure, whether it is read-only, any API limitations, or pagination behavior. The description is vague about what exactly is returned (index levels vs. change events).

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 two sentences and front-loaded with the main action. The first sentence redundantly repeats the tool's name and API reference, but the second sentence adds useful detail about additions and removals. Overall, it is concise but could be tightened by removing the redundant API mention.

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 and no annotations, the description should provide a complete picture of what the tool returns. It mentions additions and removals but does not describe the data format, time range, or whether it includes historical index levels. Given the low complexity (0 params), it is adequate but has clear gaps in explaining the exact output.

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?

There are zero parameters, so the input schema is empty (100% coverage). The baseline for 0 parameters is 4, and the description adds no confusing parameter information. It does not mislead, but it also does not add any behavioral value regarding parameters since there are none.

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 states the tool retrieves historical S&P 500 index data, specifically including additions and removals of companies. This distinguishes it from siblings like getHistoricalDowJonesChanges and getHistoricalNasdaqChanges, and the verb 'Retrieve' is specific and action-oriented.

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 implies usage for analyzing historical S&P 500 index changes, but it does not explicitly compare with alternatives such as getHistoricalDowJonesChanges or getHistoricalNasdaqChanges, nor does it state when not to use this tool. There is no direct 'use when' guidance or exclusions.

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