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

Beyond the readOnlyHint annotation, the description adds useful behavioral details: unrequested modules are omitted, requested-but-unavailable modules are named explicitly, and ratios use percentage points. This provides insight into output behavior without contradicting 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 three sentences, each containing specific, non-redundant information. It is front-loaded with the core purpose and avoids filler or repetition of schema fields.

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 the output schema exists, the description need not explain return values in detail. It adequately covers modularity, exactness, unavailable-module behavior, units, and read-only nature, making the tool's behavior clear for a snapshot tool with only two parameters.

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 adds meaningful semantics for the 'include' parameter by explaining its effect on the response (modules omitted or named if unavailable) and by listing module examples. It also clarifies 'exact' ticker matching beyond the schema's description.

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 uses a specific verb ('Fetch') and resource ('modular snapshot for one exact ETF listing'), which clearly distinguishes it from sibling tools like get_etf_holdings or get_etf_risk. It communicates both the action and the exact scope of the tool.

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 phrase 'one exact ETF listing' implies the tool is for precise lookups, but it does not explicitly state when to prefer this tool over alternatives, nor does it mention exclusions or alternative tools. The usage context is implied, not explicitly contrasted with siblings.

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