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

Annotations already declare readOnly/openWorld/non-idempotent/non-destructive, and the description goes further by noting each call is charged and repeats are not free, which explains the idempotentHint=false in practical terms. It also documents the 400-and-uncharged behavior for malformed addresses and the x402 pricing model. The remaining gap is what the success payload looks like beyond 'bytecode size' and proxy info.

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?

Front-loaded with the operation, then usage, then error behavior, example and pricing, so an agent can stop reading early. The pricing sentences are dense and slightly over-detailed for tool selection, but they carry real behavioral information.

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-only tool with no output schema, the description covers purpose, returns (bytecode size, proxy status, implementation), error behavior, cost and safety. Nothing material an agent needs to invoke it correctly 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 there is only one parameter, so the baseline is 3; the description adds a concrete example address and states the malformed-address failure mode, which gives the agent a validation signal the schema does not. It does not say whether non-0x inputs like ENS names are accepted.

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: check if a 0x address on Base is a contract or plain wallet, returning bytecode size plus EIP-1167 minimal-proxy status and implementation address. That is enough to separate it from balance/token siblings and from the risk-oriented check_counterparty.

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?

Explicitly names the trigger ('before sending funds or approving a spender') and routes the agent to check_counterparty when a full risk verdict is wanted. The only small gap is that it does not contrast itself with the sibling base_proxy tool, which also deals with proxies.

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