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

Beyond the annotations (which already declare readOnly/idempotent/non-destructive/closed-world), the description discloses determinism ('pure arithmetic — no I/O and no external calls'), rounding to 2 decimals, no auth or rate limits, and explicit failure semantics (unknown method or missing method-required parameter returns an error instead of a value). This is a rich behavioral profile an agent cannot infer from the structured fields alone.

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?

Dense but every sentence carries information: method mapping, usage routing, units, error behavior, and return shape. It is somewhat long for one paragraph, though the per-method mapping and the exclusion are front-loaded enough to scan.

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?

Complete for a 10-parameter conditional calculator: an output schema exists so return values need not be detailed, yet the description still names the key return fields, and it covers units, required-vs-optional handling, defaults, and error cases.

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, but the description adds genuinely new semantics the schema does not express: the per-method parameter groupings (ppp → spot_rate + inflation_foreign + inflation_domestic, etc.), that only method is required, that non-selected parameters should be omitted with defaults applied, and the fraction/[0,1] input conventions.

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?

Opens with a specific verb+resource pair ('Cross-border adjustments') and enumerates the three concrete methods (PPP, country risk premium, international CAPM). It explicitly distinguishes itself from valuation_capm, so an agent can route 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?

States when to use it ('cross-border cash flows and country risk'), names sibling companions ('pair with valuation_capm and valuation_time_value'), and gives an explicit exclusion with the correct alternative ('Not for the domestic cost of equity — for that use valuation_capm').

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