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

The annotations already declare readOnlyHint, idempotentHint, closed-world and non-destructive behavior, so the safety profile is covered. The description contributes the default 12-month window and the 1-120 cap, but says nothing about ordering of the returned series, price adjustment, currency or handling of non-trading days.

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 short sentences with the core resource first and the time-window constraint second; nothing is padded. The bilingual repetition adds slight redundancy but is low cost.

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 simple two-parameter read tool with no output schema, the description covers what is returned (a daily close series) and the time-range control. Missing details such as currency and series ordering are modest gaps rather than blockers.

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 50%: the months parameter is already documented in the schema, and the description mostly restates its default and ceiling. The required code parameter has no schema description at all, and the description only hints at its meaning via 'Taiwan ETF', without stating the expected code format.

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 gives a concrete verb and resource: retrieve an ETF's daily closing-price series, with the default window stated up front. The 'Taiwan ETF' qualifier separates it from fund_nav_history, though it never names a sibling explicitly.

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?

Usage is only implied: an agent can infer this is for historical ETF prices rather than ETF metadata lookups, but the description never states when to choose it over etf_lookup, fund_nav_history or data_series. No prerequisites or exclusions are given.

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