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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), and the description adds the things they cannot: a concrete price ($0.01 USDC on Base), a payment/auth requirement, and the fact that the first call is free and fails with PaymentRequired. It also discloses the extra per-chain contract-address output, which is not visible any other way.

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?

Three sentences, front-loaded with what the tool returns, then cost, then the payment handshake. The only waste is the redundant restatement of the price ($0.01 USDC ... Price: $0.01), which repeats information already given.

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?

There is no output schema, so the description carries the return-value burden, and it does name the payload (native balance, USDC balance, is-contract flag, per chain). It stops short of the actual response shape or how a partially failing chain is reported, which keeps it from a 5.

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 67%, and the description goes beyond the schema by documenting the _meta["x402/payment"] transport path that the x402_payment parameter exists to work around. The chains parameter's default (

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 a specific resource and scope: native and USDC balances of an EVM wallet across five explicitly listed chains, plus a per-chain contract check, all in one call. That is concrete enough to separate it from siblings like token_safety_check or crypto_address_validate without opening any 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?

The x402 flow is spelled out procedurally: first call returns PaymentRequired with no charge, then retry with payment in _meta["x402/payment"]. That is real invocation guidance, but there is no statement of when this tool is preferred over the sibling tools that also accept addresses.

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