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

With no annotations, the description carries the full behavioral burden and does well: it discloses the cost ($0.001 per call), the payment rails (USDC on Arc/Base/Solana, XNT on X1), and the mandatory two-step payment protocol. It omits failure modes, rate limits, and confirmation of read-only-ness, so it falls short of a 5.

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?

Two sentences, front-loaded with the core question and its answer set, then the payment mechanics. The parenthetical enumerating payment tokens is dense but genuinely necessary for the agent to proceed. No filler sentences, though the payment clause is slightly stacked.

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?

No output schema and no annotations exist, so the description must stand alone; it names the returned fields (code size, proxy implementation, delegation) and the pricing/payment contract. It never sketches the response shape or units (e.g., whether code size is bytes or whether a non-contract returns zero), leaving a small gap for a fully self-sufficient definition.

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 the baseline is 3. The description adds real meaning beyond the schema by explaining why `payment` is optional and what the no-payment call returns (payment terms), turning a bare 'signed x402 payment' field into an actionable two-phase workflow. It adds a bit less for `chain` and `address`, which the schema already documents.

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 opens with a precise verb+resource question ('Is this address a contract') and enumerates the exact outputs: code size, EIP-1967/ZeppelinOS proxy implementation, and EIP-7702 delegation. It also names the supported chains, which cleanly separates it from siblings like evm_call or evm_token_info that read state rather than inspect bytecode.

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?

Usage is well-scoped: call it to determine contract-ness or resolve a proxy implementation, and only on the four listed chains. The x402 handshake ('call once without payment for the terms, sign them with your own wallet, call again with payment') tells the agent exactly how to invoke it. It stops short of explicitly contrasting with sibling tools like evm_call, so not a 5.

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