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

With no annotations, the description must carry the load, and it does disclose the pricing model (0.001 USDC per call via x402), which is meaningful behavioral context. However, it omits the two-step payment handshake, what happens when the proof is missing or invalid, and only loosely characterizes the returned values despite there being no output 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?

Two short sentences: outputs first, pricing second. Nothing is padded and the key facts are front-loaded.

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 small deterministic calculator with a fully populated input schema, this covers what the tool produces and its cost. The main residual gap is the paid-call workflow and the undocumented periodsPerYear, which the schema only partially compensates for. No output schema exists, so describing the return set here is appropriate and mostly done.

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 80%, so the schema already defines principal, ratePct, years, and the paymentProof flow. The description adds no parameter meaning beyond the schema, and periodsPerYear (with its default) is undocumented in both places. Baseline 3 applies.

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?

The description names the concrete outputs (fixed periodic payment, total interest, amortization summary) for a loan, which distinguishes it from a generic interest calculator. The verb is only implied ('compute'), but the resource and result set are clear. A sibling like compound_interest is implicitly differentiated by the amortization/payment focus.

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?

It gives no guidance on when to choose this over the adjacent compound_interest tool, nor any prerequisites besides the fee. The x402 payment flow (first call returns 402, then retry with proof) is behavior an agent must follow but is never mentioned in the description.

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