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

Annotations already declare readOnly, idempotent, non-destructive, closed-world, so the safety profile is covered. The description adds genuinely useful behavior beyond that: 'the window is set by the youngest holding' and that weights vs amounts yield the same answer here. It does not, however, discuss output granularity or cost/latency for what is clearly a heavy computation.

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?

Front-loaded with the core purpose, then usage, then caveats, with no filler sentences. The opening clause ('from how their prices moved together rather than how many tickers there are') is a touch convoluted but earns its place as the key differentiator.

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 parameters are fully documented in the schema. The description covers purpose, usage, sibling routing and the window rule; only deep output-shape or performance expectations are absent, which is acceptable given the output schema.

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 100%, so both parameters are already documented (base currency, holdings map with ticker conventions). The description only restates base's role and default, adding the mildly useful note that weights and amounts give the same answer. Baseline 3 is appropriate when the schema does the heavy lifting.

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, non-obvious verb+resource: the effective number of independent bets derived from co-movement rather than ticker count, plus per-holding risk share vs money share. It explicitly distinguishes itself from measure_portfolio, which is named as the superset that also includes look-through and crises.

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?

Gives concrete user questions it answers ('am I diversified?', 'which holding carries the risk?') and names the alternative with the condition that selects it (measure_portfolio includes this plus look-through and crises). An agent can route between the two without inspecting schemas.

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