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

Annotations only declare readOnlyHint=true. The description adds meaningful behavior beyond that: the two-step x402 payment handshake, where the first call returns payment terms rather than the data, and the exact location for the signed payment. This is non-obvious and would trip up an agent that didn't know it.

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 first two sentences are near-duplicates, restating that this returns the total supply of an ERC-20 contract. That redundancy costs space without adding information, though the endpoint and payment-flow sentences are load-bearing and reasonably front-loaded.

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 read-only, single-parameter tool, the safety and payment mechanics are covered, but there is no output schema, so the description leaves the return shape (e.g., a decimal string vs. raw uint256, and how to interpret it) unspecified. Adequate but not fully complete.

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?

There is a single parameter with 100% schema description coverage ('ERC-20 contract, 0x + 40 hex'), so the schema already documents it fully. The description repeats 'given token address' without adding format, validation, or example detail beyond the schema.

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 totalSupply), resource (ERC-20 token contract), and scope (Ethereum mainnet), which cleanly distinguishes it from sibling reads such as erc20_balanceof, erc20_allowance, or eth_getcode. An agent can identify the tool's purpose without opening the 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?

The description details the protocol-level usage pattern (call once unpaid to obtain payment terms, then retry with a signed payment in _meta['x402/payment']), which is genuinely useful procedural guidance. However, it gives no guidance on when to choose this tool over sibling reads like balanceof or contract_abi — that selection is left to inference from the name.

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