etf_analysis

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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. Beyond that the description adds genuinely useful behavior: the benchmark is converted to the fund's currency, and tracking difference is defined as fund minus benchmark on an annualised basis — details an agent could not infer from structured fields.

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 tight sentences that front-load the metric list before the benchmark advice. Nothing is padded, though the parenthetical definition adds a clause that could be trimmed without loss.

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?

With no output schema, the description does the work of telling the agent what comes back (TER, tracking difference, tracking error) and in what convention. The main omission is the period parameter's accepted values, which leaves one of three inputs underspecified.

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 0%, so the description carries the burden. It explains the benchmark parameter's semantics well (currency conversion, total-return preference) and implies ticker meaning, but 'period' is left completely undocumented — its default '3y' and accepted formats/values are nowhere stated, which is a substantive gap for a 3-param 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?

Names a specific resource (ETF cost and replication quality) and enumerates the exact metrics produced: TER, tracking difference (fund minus benchmark, annualised) and tracking error versus a benchmark ticker. This is clearly distinguishable from siblings like risk_metrics or fundamental_ratios, though it never explicitly positions itself against them.

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 final sentence gives real guidance on benchmark selection ('prefer a total-return index or a reference ETF on the same index'), which is a meaningful usage constraint. However, there is no statement of when to choose this tool over risk_metrics or peer_comparison, nor any prerequisite or exclusion, so usage is only implied.

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