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

Annotations already declare readOnlyHint and openWorldHint, but the description adds critical context beyond them: determinism/no LLM, a concrete example return shape, and an explicit payment requirement (x402, $0.0025 USDC, passed via _meta["x402/payment"]). The paid-call auth/payment detail is exactly the behavior an agent cannot get from annotations.

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?

One dense paragraph: purpose and chains first, then determinism, then output example, then price. Every element (including the example and the payment note) carries information the agent needs, with no filler.

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?

No output schema exists, and the description compensates with an inline example response covering chain, contract, tokenId and owner. Combined with the payment details and chain coverage, an agent has everything needed to call it correctly.

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, tokenId (decimal), and contract. The description repeats the chain list without adding format or constraint detail, so the baseline of 3 applies.

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 the specific verb+resource ('Current owner of an ERC-721 token') and names the exact underlying call (ownerOf), plus the supported chains. This is unambiguously separable from sibling tools like nft_metadata or token_safety.

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?

Usage is implied by naming the ERC-721 ownerOf semantic and the supported chains, which tells an agent what the tool can answer. There is no explicit when-to-use/when-not guidance and no named alternative (e.g. nft_metadata for attributes), so routing relies on inference.

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