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

Annotations already declare readOnlyHint and openWorldHint, so the safety and external-data profile is covered. The description adds one useful trait beyond the annotations – the caveat 'when Yahoo provides them' – which warns the agent that results may be absent for some symbols, but it says nothing about the shape, timing, or coverage of the events.

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?

A single front-loaded sentence with no filler. The resource and its scope come first, and the availability hedge is appended efficiently.

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?

An output schema exists, so return values need no explanation, and the one input parameter is fully documented in the schema. For a simple single-parameter lookup the definition is nearly complete; only an availability/frequency note beyond the terse hedge would improve it.

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 100% and there is only one parameter, so baseline would be 3, but the description adds real meaning: it narrows valid inputs to ETF or mutual fund symbols, which corrects the schema's example of AAPL (an equity, not a fund). That is a meaningful constraint not present in the schema text.

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?

States a specific verb ('Returns') and resource ('capital gain events') and scopes it to ETF/mutual fund symbols, which distinguishes it from the many sibling ticker tools like yahoo_finance_ticker_dividends and yahoo_finance_ticker_splits. It does not name those siblings explicitly, but the resource type is unambiguous.

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 implied by the resource: fetch capital gain distributions for a fund symbol. But there is no explicit when-to-use guidance, no statement of prerequisites, and no routing to alternatives such as the dividends or splits endpoints.

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