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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds real behavioral context beyond that: the yearly-period assumption and a pointer to an interactive version. It omits failure behavior (e.g. no real IRR / non-convergence / multiple roots), which is the one meaningful gap.

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 definition, then the sibling routing rule, in two tight sentences. The interactive URL is a minor extra that does not help an agent invoke the tool, but it costs little and does not obscure the actionable content.

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-only calculation the definition is nearly sufficient, and the schema covers inputs fully. However, there is no output schema, so the description should say what comes back (decimal vs. percentage, error when no IRR exists) — that return-shape ambiguity is left unresolved.

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%, and both parameters are already documented with sign conventions and year-0/year-1 ordering. The description's phrase 'evenly spaced yearly' reinforces the timing convention but adds no syntax or format detail the schema does not already carry, so the baseline 3 applies.

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 metric and the exact input convention it expects: IRR for evenly spaced yearly cash flows after an initial investment. It immediately distinguishes itself from the sibling xirr, so an agent can pick the right one without opening either schema.

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?

Explicitly names the alternative (xirr) and the exact condition that selects it: cash flows with specific dates or irregular timing. That is a textbook when/when-not routing rule with nothing left to inference.

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