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

Goes well past the annotations: discloses pricing ($0.01/call via x402 or credits, first 25 free, failed calls free), error semantics (404 for no contract, 422 for a non-ERC-20 contract, both uncharged), and confirms nothing is mutated. 'Each call is charged, so repeats are not free' also explains the otherwise puzzling idempotentHint=false.

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-loads the result shape and the sibling distinction, which is the right ordering, and every clause carries information. It is a dense single paragraph with mild redundancy — pricing is stated and then restated as 'each call is charged, so repeats are not free'.

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 correctly compensates by describing the return fields, and it covers errors, cost, and the sibling alternative. The only substantive gap is the mischaracterization of the token parameter's accepted forms, which is the one thing an agent could get wrong when calling.

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 does add the 40-hex-character address format, but its claim that 'Both inputs are 0x addresses' conflicts with the schema's token parameter, which accepts tickers like USDC or WETH — an agent reading only the prose could wrongly reject a ticker input.

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 (fetch an ERC-20 balanceOf result for a wallet on Arbitrum One) and enumerates exactly what comes back: raw amount, decimals, symbol, human-readable amount. It explicitly separates itself from arb_balance for the native coin, so an agent can pick it over the dozens of sibling *balance tools without opening any schema.

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 use case ('check stablecoin or token holdings before a transfer or trade') and names the alternative with the condition that selects it ('for the native coin use arb_balance'). None of the other 90+ siblings are confused with it.

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