irrInternal rate of return: the per-period rate that zeroes the NPV of a cashflow series. Returns a percent, or null when the series never crosses zero.
| Name | Required | Description | Default |
|---|---|---|---|
| cashflows | Yes | Cashflows by period, starting at period 0. Outflows are negative. |
| Name | Required | Description | Default |
|---|---|---|---|
| irrPct | No | Internal rate of return, percent (null if none). |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Beyond the annotations (readOnly, idempotent), the description adds the key behavioral detail that it returns null when the cashflow series never crosses zero, and clarifies the result is a percentage. No contradictions 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?
The description is a single sentence, front-loaded with the term definition, and every clause contributes meaning. No 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?
Given the output schema exists and the parameter is documented, the description covers the essential behavior (percent return, null case). It doesn't address edge cases like multiple IRRs, but that's beyond the minimum for a simple financial tool. Sibling context implies regular periods are assumed, which aligns.
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 only parameter `cashflows` is fully described in the schema with period and sign conventions. The description adds no additional parameter-level meaning, but the high schema coverage carries the burden, so baseline 3.
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 gives a precise mathematical definition of IRR, clearly stating what it computes and the return type. It implies regular periods via 'per-period rate' but does not explicitly contrast with XIRR or MIRR, so it falls short of full sibling differentiation.
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?
No guidance is provided on when to use IRR versus alternatives like XIRR (irregular intervals) or MIRR (reinvestment assumptions). The schema's 'by period' hint is subtle but not explicit in the description.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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