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

Beyond the readOnlyHint annotation, the description discloses important behaviors: unavailable series are named explicitly and never approximated, and series are returned only when source data or explicit benchmark ticker exists. This adds significant transparency about conditional behavior and data quality, exceeding what annotations provide.

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 concise sentences: core function, conditional behavior, and read-only safety. Every sentence adds distinct value with no redundancy or fluff.

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 tool's complexity, output schema existence, and readOnly annotation, the description covers the key behavioral rules not in the schema. It explains conditional availability and the no-approximation policy, making the tool complete for selection and invocation without needing return details.

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 57%, so the description compensates by clarifying the series parameter (never approximated) and benchmarkTicker (explicit ticker needed). It does not explain startDate, endDate, or limit, but these are relatively self-explanatory or covered by schema defaults.

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 fetches ETF price or price-return history at daily, weekly, or monthly intervals. It specifies the exact resource (ETF time series) and the action (fetch), distinguishing it from siblings like get_etf_holdings or get_etf_snapshot, which focus on other data types.

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 when to use this tool (for time series data) and provides context about when additional series like NAV or benchmark are available. However, it does not explicitly name alternative tools for other use cases or state when not to use this tool, so it lacks explicit exclusions or alternatives.

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