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

Annotations already declare a safe read-only, idempotent, closed-world operation, and the description adds substantial context beyond them: determinism, the optional after-tax mode, the year-by-year tables, the break-even residual output, and possible warnings. It also tells the agent to cite the formula version, which is genuine behavioral guidance.

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 the core comparison, then the determinism/citation instruction. The first sentence is long and parenthetical-heavy, but nearly every clause carries model detail that the schema does not restate in aggregate.

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?

Even with no output schema, the description explains what comes back (year-by-year tables, break-even residual, steps, warnings) and how the two cases are constructed. For a complex nested four-parameter model with full schema coverage, an agent has what it needs to call it correctly.

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 parameter-level meaning is already covered. The description still adds model-level semantics by mapping which inputs belong to which cash-flow stream (rent, free rent, tenant expenses, move-in costs vs. equity, debt service, reserves, sale) and clarifying the after-tax toggle, going beyond the field descriptions.

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 and comparison (lease vs. own over a fixed horizon) and enumerates the cash-flow components of each case, including the horizon sale via stated value or exit cap rate. An agent can distinguish this from generic calculators such as calc_npv or calc_renew_vs_relocate without opening the 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?

Explicitly directs the agent to use this rather than doing the math manually and to cite formula calc.lease_vs_own@2 and surface warnings. It does not, however, state exclusions against close siblings like calc_renew_vs_relocate or calc_npv, so the when-not guidance is partial.

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