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

Annotations already cover the safety profile (readOnly, non-destructive, openWorld), yet the description adds substantial value beyond them: it discloses the per-call price ($0.0045 USDC), the x402 payment rail and currencies, that compliant clients pay automatically, and that the address is verified to be a contract. Payment/auth requirements are exactly the kind of behavioral context annotations cannot express.

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 purpose, then params, then payment, then a runnable sample. It is slightly long, but the payment details and example input earn their place for an agent, so only minor trimming is possible.

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?

There is no output schema, so the description correctly carries the return-value burden by listing the fields returned (name, symbol, decimals, total supply, optional balance). Combined with payment, chain, and contract-verification info, it is nearly complete, with only the remaining edge-case behavior (e.g. failure when the address is not a contract) left unstated.

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 67% and the description restates the parameters (token required contract address, chain default base, holder optional address). It usefully fills the gap for the enum-only chain param by naming the default, but it adds little beyond the schema for token and holder, so baseline 3 is appropriate.

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 (Read) and resource (ERC20 token contract), and enumerates exactly what it returns: name, symbol, decimals, total supply, and optional holder balance. This clearly distinguishes it from siblings like evm_balance (native balance) and erc20_transfers (transfer history), which an agent can tell apart without opening 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?

The description gives context (which chains are supported, the optional holder lookup, and the free sample) but never states when to use this tool versus alternatives such as evm_balance or erc20_transfers. Usage is implied rather than routed, so it lands at the minimum-viable level.

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