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

Annotations already mark it read-only, idempotent, and non-destructive. The description adds valuable behavioral context: it covers all US ETFs the server can answer for, discloses data freshness, and explains the two data sources (issuer daily files vs. SEC filings). This goes beyond the annotations and clarifies what the tool actually returns.

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 tight sentences, with the core purpose and output context front-loaded, followed by a direct usage directive. No filler or redundant restatement of the title.

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 no-parameter listing tool, the description fully covers what the list contains, data provenance, and when to invoke it. No output schema exists, but the description supplies enough for an agent to understand the expected result.

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 no parameters, so the schema imposes no burden. The description focuses on the output and scope instead, which is appropriate for a zero-parameter tool.

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 states a specific function: list every US ETF the server can answer for, including data date and holdings source. It clearly distinguishes this as a coverage-listing tool from the sibling comparison and analysis tools.

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?

It gives an explicit call condition: 'Call it when you are not sure a fund is covered.' It does not mention alternatives or when not to use it, but the context is clear enough for an agent to select this tool for coverage checks.

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