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

Annotations already declare open-world, non-idempotent, non-destructive behavior, so the bar is lower; the description adds real context by disclosing a hard payment requirement ($0.001 USDC on Base per successful call via x402), which is a consequential trait not captured by any structured field. It stops short of describing error behavior (e.g., non-existent addresses) or confirmation timing, and the readOnlyHint=false annotation for what reads as a pure query goes unclarified.

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, both front-loaded: the capability and its return fields first, then the usage trigger, then the cost. No filler and nothing redundant with the schema or annotations.

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 carries the return-value burden and does it well by naming bytecode size, proxy status, and implementation address. For a paid, open-world query it omits only edge-case behavior (nonexistent address, non-Ethereum input) and what happens if payment fails.

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 description coverage is 100% and the schema documents the single required 'address' (0x address) parameter, so the baseline is 3. The description adds no format detail (e.g., checksummed vs. lowercase, ENS support) beyond what the schema already provides.

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 (check whether an Ethereum address is a contract) and enumerates the exact outputs: bytecode size, EIP-1167 minimal-proxy detection, and the implementation it points to. The 'on Ethereum' scoping distinguishes it cleanly from arb_is_contract, base_is_contract, op_is_contract, and polygon_is_contract siblings.

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?

Gives a concrete when-to-use trigger: 'Use before sending funds or approving a spender,' which tells the agent the decision this tool informs. It does not explicitly exclude or compare against the other chains' is_contract tools, but the chain qualifier makes the selection inferable.

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