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

With no annotations, the description carries the full burden and does reasonable work: it discloses the read-only mechanism (eth_call / balanceOf), the return shape (raw amount plus decimals), and a concrete cost model ($0.005 per call via x402/USDC). It doesn't state chain defaults or failure behavior for invalid contracts, but the cost and mechanism disclosure is genuinely useful context beyond the schema.

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 core purpose, and every sentence adds something. Minor redundancy in repeating the eth_call/balanceOf mechanism twice, but the pricing and return-format notes are justified.

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 3-parameter read tool with full schema coverage but no output schema, the description usefully describes the return value (raw amount + decimals) and the cost, which is what an agent would otherwise lack. Leaving the chain parameter's default unstated is the main remaining gap.

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%, so the schema already documents chain, token, and address. The description only adds token examples (USDC, USDT, DAI) without explaining the chain parameter's default or valid range, so it sits at the baseline for high-coverage schemas.

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 the ERC20 balance for a wallet — and pins the mechanism (balanceOf via eth_call). The 'ERC20' qualifier implicitly separates it from evm_balance (native) and evm_erc20_allowance, but no sibling is named explicitly, so the differentiation is inferred rather than stated.

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?

There is no when/when-not guidance and no named alternative. The list of sample tokens (USDC, USDT, DAI) implies the tool is for token lookups, but an agent gets no help deciding between this, evm_balance, evm_erc20_allowance, or evm_token_info.

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