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

Annotations cover the safety profile, but the description adds material context they don't: a $0.001 USDC-on-Base charge per successful call settled via x402, meaning the agent must be prepared to pay. It also discloses the return content (bytecode size, proxy status, implementation), which matters since there is no output schema. It does not reconcile the readOnlyHint=false annotation with what reads like a pure lookup.

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 tight clauses: what it returns, when to call it, what it costs. No filler, and the most decision-relevant information (result shape and payment) is front-loaded.

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 no output schema, the description fully carries the return-value burden by enumerating contract/wallet, bytecode size, proxy flag, and implementation. The payment requirement, which an agent must know before invoking, is also present.

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?

Single parameter with 100% schema description coverage, so the schema already documents the 0x address. The description only implies the address must live on Optimism; it adds no format or validation detail beyond the schema, which is the expected baseline here.

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 (address on Optimism → contract vs. wallet) and explicitly names the extra payload: bytecode size, EIP-1167 minimal-proxy detection, and implementation address. The chain qualifier cleanly separates it from eth_is_contract, base_is_contract, arb_is_contract, and polygon_is_contract.

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?

"Use before sending funds or approving a spender" gives a concrete trigger for calling it, which is real guidance. It stops short of naming when NOT to use it or pointing at the other chain-specific is_contract siblings, so it is clear context without exclusions.

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