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

Annotations already declare readOnlyHint=true and idempotentHint=true, setting the safety context. The description adds behavioral value by specifying the output unit ('annual rate') and the null behavior when no rate fits, which is useful beyond what annotations provide.

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?

The description is a single, front-loaded sentence that efficiently conveys purpose and a key edge-case behavior. Every clause adds meaning, with no redundancy or filler.

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?

With a full input schema and read-only/idempotent annotations, the description covers what the tool does, the input nature, and the null result case. It is slightly less explicit about differentiation from related tools like 'irr' or 'xnpv', but overall it is complete for a calculator of this simplicity.

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?

The input schema already describes all parameters thoroughly: 'cashflows' as an array with 'date' (ISO date) and 'amount' (outflows negative), plus the note that the first date is the valuation date. The description's mention of 'irregular dated cashflows' reinforces the date-aware nature but adds no new parameter-level semantics.

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 what the tool does: computes a date-aware internal rate of return that zeroes the XNPV of irregular dated cashflows. It uses a specific verb ('returns') and resource ('internal rate of return'), and the phrase 'Date-aware' distinguishes it from the sibling 'irr' tool.

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 implies the tool is for irregular dated cashflows by emphasizing 'Date-aware' and 'irregular dated cashflows', which gives clear context for when to use it. However, it does not explicitly name alternatives like 'irr' for regular periodic cashflows, so it stops short of full exclusion guidance.

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