finance.fv

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

Goes well beyond the readOnly/idempotent annotations: it discloses 50-digit internal precision independent of caller settings, that out-of-range computation is treated as an input error, default rounding behavior (HALF_EVEN to decimals), and that amount/rate must be finite. Those are real behavioral traits an agent could not infer from annotations or schema.

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?

Formula and core purpose are front-loaded, then parameter formats, then precision/rounding, then the unit-mismatch warning — a sensible order with no filler sentences. Density is high and a couple of constraint clauses could be tightened, but nothing is wasted.

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 a 5-parameter tool with an output schema and annotations already present, the description fills the remaining gaps: input formats, numeric constraints, rounding/precision semantics, and error conditions. An agent has everything needed to invoke it correctly; return values are covered by the output schema.

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 0%, so the description must carry the load, and it documents all five parameters: Decimal-string types for present_value and rate, rate >= 0 with example 0.05, periods as integer >= 1, decimals default 2 and non-negative, rounding default HALF_EVEN. The one gap is that accepted rounding mode values are never enumerated, so an agent must guess valid strings beyond the default.

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 verb+resource (compute future value) and gives the exact formula FV = PV x (1+r)^n with per-period compounding. The direction of the calculation (PV -> FV) distinguishes it from the sibling finance.pv without needing to open 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?

Usage is implied by the stated formula rather than spelled out; there is no explicit 'use this when' or reference to alternatives such as finance.pv or finance.cagr. The one caution — do not mix unit bases such as an annual rate with a monthly period count — is genuine usage guidance, but it is the only one.

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