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

Annotations only cover readOnlyHint=true, but the description adds substantial context beyond that: the two-step payment flow, the payment channel, the endpoint route, and the exact measured output shape. This is exactly the behavioral detail an agent needs to call and pay for the tool correctly.

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 is front-loaded in the first sentence, and the payment instructions follow logically. The 'Measured output' JSON is redundant in places (hex and result are identical) but earns its place given there is no output schema.

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 single-parameter read with no output schema, the description supplies everything needed: the request format, the chain, the exact response payload, and the payment protocol. Nothing essential to correct invocation is missing.

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% and the single 'address' parameter is fully documented in the schema with the same '0x + 40 hex' format note restated in the description. The description adds no new semantics beyond the schema, 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+resource ('the deployed bytecode at an address') and names the underlying RPC method (eth_getCode) and chain (Ethereum mainnet). This clearly distinguishes it from siblings like eth_mainnet_contract_abi or erc20_balanceof, which return different data.

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?

Provides strong operational guidance for the x402 payment handshake: call once with no payment to obtain terms, then retry with the signed payment at _meta['x402/payment']. However, it never explicitly states when to prefer this tool over a sibling (e.g., bytecode vs ABI), so the alternative-selection case is absent.

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