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

Annotations already declare readOnly/openWorld/non-idempotent, and the description adds substantial new context: 404 for a missing contract, 422 for a nonexistent token, both uncharged, $0.01/call via x402 or card key, first 25 free, failed calls free, and an explicit warning that repeats are billed. That is exactly the cost and failure behavior an agent needs before calling.

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 alternatives, then error semantics, then pricing. Dense but nearly every clause carries new information; the closing pricing sentence stacks several facts and could be split for readability.

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, and the description compensates by naming what is returned: the owner address plus the collection's name and symbol. Combined with error codes, pricing, and exclusions, an agent has everything needed to call this 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 coverage is 100%, so the parameters are already documented; the description still adds a concrete worked example with a real contract address and tokenId, plus the clarification that tokenId is a whole number identifying one ERC-721 token. Useful but not beyond what a strong schema plus example can convey.

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?

"Owner of an NFT on Optimism: the wallet that holds one ERC-721 token id right now (ownerOf), plus the collection's name and symbol" names the specific verb, resource, chain, and the exact on-chain call used. It is unmistakably distinct from the sibling metadata and balance tools.

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?

It states the intended use case (verify holder before a trade, mint gate, airdrop) and explicitly routes to siblings with conditions: "for how many a wallet holds use op_nft_balance, for the token's metadata op_nft_metadata." Nothing is left to inference.

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