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

Annotations already mark this as read-only/idempotent/non-destructive. The description adds useful behavioral context: it covers three years of prices, supports a fund ticker on one side, reports fund weight/rank, and notes the 'covered US ETFs' limitation. No contradiction with annotations.

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 with no filler. The main deliverable is front-loaded in the first sentence, the ETF special case in the second, and the sibling routing in the third. Every sentence earns its place.

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 two-parameter read-only tool with no output schema, the description provides a solid account of what will be returned and the one special-case input mode. It could be more explicit about exact output shape, but the listed metrics and ETF behavior cover the agent's invocation needs well.

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%, so the baseline is 3. The description adds meaning beyond the schema by clarifying that ticker 'a' may be an ETF ticker, that only one side can be a fund, and that two ETFs should go to compare_funds. This goes beyond the schema's simple 'ETF ticker also works' note.

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 it compares two US stocks or a stock and an ETF, and enumerates the specific metrics returned (market cap, valuation, returns, volatility, beta, correlation, ETF holdings). It also distinguishes itself from compare_funds 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?

The description gives explicit routing guidance: 'For two ETFs use compare_funds' and explains that a fund ticker can be used on one side. It does not enumerate all sibling alternatives, but the key distinction from the closest sibling is clear.

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