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

Beyond the readOnlyHint annotation, the description adds meaningful behavioral context: leaders are mechanical extrema (not recommendations), and currency/partial-holdings caveats are explicit. This helps the agent understand output limitations and interpretation, going beyond the annotation.

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?

Three dense sentences: the first delivers the core function, the second preempts misinterpretation of 'leaders', and the third flags caveats and read-only nature. No redundancy or filler.

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 presence of an output schema and readOnlyHint annotation, the description adequately covers purpose, scope, and interpretive caveats. It does not explain performanceDays or error conditions, but those are partially represented in the schema and output schema, so the overall context is sufficient.

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 only 33%, so the description must compensate. It lists the modules that map to the 'include' enum and states the ticker count range, adding meaning to those params. However, it completely omits the 'performanceDays' parameter, leaving its semantics to the schema's numeric constraints alone.

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 verb ('Return'), a resource ('two to ten ETFs'), and a clear scope ('normalized side-by-side comparison across selected modules'). This distinguishes it from siblings like get_etf_snapshot or analyze_etf_overlap by emphasizing multi-ETF comparison.

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 clearly implies when to use the tool (comparing multiple ETFs across modules) and provides a caution about leaders being mechanical extrema, but it does not explicitly name alternative tools or state when not to use it. This matches 'clear context, no exclusions'.

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