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

Discloses behavior that no annotation provides: a per-call price ($0.01 USDC), the x402 challenge-then-retry handshake with the exact _meta["x402/payment"] key, and an HTTP fallback. That is exactly the kind of non-obvious protocol detail the description should carry, and it is consistent with readOnlyHint=false since a call spends funds.

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 the classification purpose before payment mechanics and the HTTP fallback. The payment sentence is dense but essential and earns its space.

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 one-parameter tool with no output schema, the description covers what is classified (EOA/contract/proxy/token) and the full payment protocol. It doesn't indicate the shape of the returned verdict, which is the only meaningful remaining gap.

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?

There is a single parameter and schema coverage is 100%, with the schema spelling out '0x-prefixed 20-byte Ethereum address.' The description adds nothing about the address beyond that, so the 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?

States a specific verb and resource plus the classification taxonomy: 'Classify an Ethereum address: EOA vs contract, proxy, token.' That is far more informative than the name alone. It doesn't name or differentiate from the nearest siblings (evm_transfers, evm_tx_decode, address_verify), so it stops short of a 5.

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 when-to-use case is implied by the enumeration of verdicts, and the HTTP equivalent is given as an alternative transport. But there is no guidance on when to pick this over address_verify or address_bundle, and no stated exclusions or prerequisites beyond the payment flow.

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