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

With no annotations, the description carries the full burden. It does disclose a non-obvious behavioral trait — the x402 payment requirement, price ($0.01/call), currency (USDC) and chain (eip155:8453) — which an agent must know before calling. However it says nothing about return format, rounding/precision, error cases, or idempotency.

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 price are front-loaded and useful, but the middle sentence ('Use this when an agent needs to future value with any compounding frequency') is redundant filler and is also grammatically broken. Roughly one of three sentences does not earn its place.

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 simple 4-param calculator with 100% schema coverage and no output schema, the description covers inputs, the payment model, and gestures at the output ('total interest earned'). It still leaves the exact response shape (principal + interest breakdown vs. single total) unspecified, which an agent would need for downstream use.

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 baseline is 3, but the description adds real meaning by decoding the enum: annual=1, semi-annual=2, quarterly=4, monthly=12, weekly=52, daily=365. The raw enum values are unlabeled strings '1','2','4','12','52','365', so this mapping is genuinely useful rather than duplicative.

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 ('Project the future value of a deposit with compound interest') plus the configurable dimension (compounding frequency) and the deliverable (total interest earned). It is clearly distinguishable from siblings like finance_cagr_calculator or crypto_apr_apy, though it never names or contrasts any sibling.

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?

The only usage sentence is 'Use this when an agent needs to future value with any compounding frequency,' which largely restates the purpose rather than giving conditions, prerequisites, or alternatives (e.g. simple-interest vs. CAGR vs. loan-payment tools). Implied usage is there, but no when-not or routing guidance.

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