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

Annotations already mark the tool as read-only and non-destructive, but the description goes far beyond that: it reveals the data provenance (SEC Form N-PORT or daily holdings file), the fact that the fund name and date are returned, that partial filings are never served, and that unmatched rows are preserved under their reported names rather than dropped. These are significant behavioral traits that an agent needs to know and are not present in the annotations.

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 long but every clause earns its place: it states the purpose, lists supported indices, explains data source, notes handling of partial filings and unmatched rows, and gives explicit alternatives—all in a logical flow. It is front-loaded with the key action and scope, and there is no redundant or filler wording.

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 tool has only three parameters, no output schema, and no nested objects, yet the description provides a thorough account of the response structure (rank, ticker, share), data provenance, and edge-case behavior (unmatched rows, partial filings). It even covers what the tool does not do via pointers to sibling tools. For a simple read-only list tool, this is complete and exceeds what is needed.

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% for all three parameters (index, offset, maxResults), and the schema already includes defaults and explanations such as 'heaviest first' for maxResults. The description does not add any new information about the parameters themselves; it only describes output structure and behavior, which is not the focus of this dimension. Thus, a baseline score of 3 is appropriate because the schema handles parameter semantics well.

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 opens with a specific verb and resource: 'Get the current constituent list of a major US stock index' and enumerates seven concrete indices, immediately making the tool's scope clear. It also distinguishes itself from siblings by referencing GetIndexChanges and GetIndexForecast as alternatives for different queries, which prevents confusion.

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?

Explicit usage guidance is provided: 'Use GetIndexChanges for what has joined or left, and GetIndexForecast for who the published rules point to next.' This tells the agent when not to use this tool and names the alternatives. The description also explains the data source (fund filings) and the guarantee about complete listings, offering clear context for when to rely on this tool.

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