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

With no annotations, the description carries the full behavioral burden. It discloses the input shape and that it 'returns the rate,' but it does not specify whether the returned rate is a decimal or percentage, the required sign convention beyond the example, or edge-case behavior such as multiple IRRs or non-convergence.

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 with a concrete example and no wasted words. The 'IRR Calc:' prefix is mildly redundant, but it does not meaningfully detract from readability.

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?

The example makes the core usage actionable, but with no output schema and no annotations, the description should clarify output units, parameter selection among the three aliases, and sign convention. These gaps leave room for an agent to call the tool incorrectly despite the clear example.

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 schema parameter descriptions are generic ('Flows to process'), and the description adds an array example and mentions 'cashflows or flows,' but it leaves the three aliases (flows, cashFlows, cashflows) ambiguous and does not reconcile the schema's 'string' type with the description's 'array' phrasing.

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 states a specific verb and resource: 'Calculate the Internal Rate of Return (IRR) from a cashflow series,' with a concrete example. It is clear what the tool does, though it does not explicitly differentiate it from sibling finance tools such as npv-calc or annualized-return.

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 intended use is clear: when an agent needs an IRR from a cashflow series, this tool performs that calculation. The example input format gives additional usage guidance. It does not name alternatives or explicitly state when not to use the tool, which keeps it from a 5.

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