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

Beyond the readOnly and non-destructive annotations, the description discloses pricing ($0.002/call, first 25 free), that failed calls are free, that malformed addresses are rejected with 400 uncharged, that each successful call is charged, and that results are at the latest block in both wei and ETH. These details materially help an agent understand cost, error behavior, and repeat-call implications.

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?

The description is front-loaded with the core operation, then usage alternatives, validation behavior, example, pricing, and safety. Every sentence adds practical information, and there is no redundant or filler content.

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 simple one-parameter balance lookup with no output schema, the description covers the chain, block scope, units, usage alternatives, validation errors, billing behavior, and read-only nature. Nothing essential for 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?

The sole address parameter is already fully described in the schema, so the baseline is high. The description still adds useful meaning by stating that any 0x wallet address is accepted, that malformed addresses are rejected with 400, and by providing a concrete example address.

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 states a specific verb and resource: native ETH balance via eth_getBalance for any 0x wallet address on Optimism at the latest block. It also names the sibling alternatives op_token_balance and wallet_portfolio, so an agent can distinguish it from adjacent tools without inspecting schemas.

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?

It gives explicit usage guidance: use it to check whether a wallet can pay gas or a transfer, and routes ERC-20 queries to op_token_balance and aggregate holdings to wallet_portfolio. This is a clear when-to-use and when-to-use-something-else statement.

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