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

Goes beyond the readOnly/idempotent/non-destructive annotations by disclosing the price ($0.007 USDC), accepted chains (Base, Polygon, Arc), and critically that the tool does not perform payment itself. That last point is behavior an agent must know and is not encoded in the annotations.

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 and price, then chain options, then the crucial 'does not pay' caveat. Two compact sentences with no filler; every clause carries actionable information.

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 an output schema present, return-value details need not be repeated, and the optional vault param is covered by the schema. The description covers cost, chains, and the payment hand-off, though it could note what the caller should do with the returned request beyond 'use your own x402 client.'

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 description coverage is 100% and the single 'vault' parameter is documented there as an optional tailoring hint. The description adds no additional semantics for it, so the baseline 3 for fully-covered schema 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?

States a specific verb and resource: it 'returns the x402 payment request for basket signals,' listing exactly what the paid call yields (rebalancing signal, momentum, suggested weights for NVDA/META/AAPL/GOOGL). The 'prepare a request, do not execute' framing clearly distinguishes it from execution siblings like stocks_basket or stocks_buy.

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 states the workflow and the exclusion: 'Pay it with your own x402 client. This tool does not pay.' This tells the agent the next step and when not to expect data. It does not name alternative prepare/check siblings (x402_check, payment_readiness) that an agent might otherwise consider.

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