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

Annotations already cover the read-only, idempotent, closed-world safety profile, and the description adds substantial context beyond them: the exact statutory basis, the payment formula, what the optional balance/rate path computes (interest subsidy, $50 principal match, 360-payment projection to payoff or cancellation), and the assumption of constant income. The provenance note (copied from statute text, not model memory) is a meaningful trust signal for a calculation tool.

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?

Purpose and statutory grounding are front-loaded, followed by formula then optional-output behavior, so the ordering is sensible. It is dense and formula-heavy in a single block, but nearly every clause conveys computational or trust-relevant information rather than filler.

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?

With no output schema, the description takes on the job of explaining returns, and it does so reasonably: base payment, first-month breakdown, and the payoff/cancellation projection. It does not describe the response shape or units for the projection (e.g., month count vs. total paid), which is a minor remaining gap for a four-parameter calculator.

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 schema carries the baseline, but the description still adds meaning: it explains that dependents subtract $50 each from the monthly figure, that rate is only meaningful together with balance, and that AGI is banded in $10,000 increments with a $120 floor and 10% top rate. That gives the agent a mental model of how each input moves the result.

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 resource (calculates the RAP monthly payment) and anchors it with the governing statute and effective date. It is clearly distinguishable from siblings like compare_rap_vs_standard and get_plan_transition_dates, which do comparison and date lookup rather than a single-payment computation.

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 formula and by the note that supplying balance and rate additionally yields a first-month and payoff projection, so an agent can infer when the optional params matter. However, it never says when to prefer this over compare_rap_vs_standard or get_plan_transition_dates, and gives no exclusions or preconditions beyond the effective date.

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