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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), and the description adds substantial behavior beyond them: pure arithmetic with no I/O, results rounded to 2 decimals, out-of-method parameters silently accepted and ignored, and error (rather than a value) on unknown method or missing required parameter. It also states the Gordon-growth constraint that discount rate must exceed perpetual growth.

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?

Front-loaded with purpose, then usage, then per-method requirements, then edge-case behavior; each block is dense and purposeful. It runs long and restates some formula/parameter detail the schema already carries, which costs a point on conciseness.

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?

For a 10-parameter, method-dispatched arithmetic tool with an output schema present, the description covers what it computes, when to use it, what each method requires, unit conventions, error behavior, and rounding. Return values need not be explained given the output schema; nothing needed to invoke it correctly is missing.

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% with per-parameter descriptions, so the baseline is 3; however, the description adds the method-to-parameter requirement mapping that the flat schema does not express (e.g. perpetuity_pv needs only payment + discount_rate, terminal_value_exit_multiple needs final_year_cashflow + exit_multiple), plus the decimal convention. That is real meaning beyond the schema, though it duplicates some formula text already in the enum description.

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 family (discount/compound/value/terminal value) over a specific resource (cash flows, annuities, perpetuities) and explicitly distinguishes itself from valuation_income_methods and valuation_discount_rate. An agent can route between this and its siblings without opening a 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?

Gives explicit when-to-use ('move cash flows through time or value a terminal value in a DCF'), names two alternatives with the conditions that select them ('uneven multi-period cash flows' -> valuation_income_methods; 'rate construction' -> valuation_discount_rate), and prescribes combining with valuation_discount_rate. Nothing is left to inference.

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