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

Adds real behavioral context beyond annotations: 404 for a missing contract, 422 for a nonexistent token, both uncharged, plus per-call pricing and the note that repeats are charged (consistent with idempotentHint=false). The description could still describe the response shape, but the safety/error/cost profile is well covered.

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?

Purpose and the two sibling alternatives are front-loaded, followed by errors, example, and pricing. Every sentence carries information, though the billing/credits sentence is somewhat dense and could be trimmed without loss.

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, and the description does state that the result includes the current owner, collection name, and symbol. Combined with the error semantics and pricing, this is nearly complete, with only the exact response field structure left implicit.

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% (contract address, token id), so the schema already documents both parameters. The example with a concrete contract and tokenId=1 is helpful but only marginally beyond the schema, so the baseline of 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?

Names a specific verb and resource ('Owner of an NFT on Arbitrum One... the wallet that holds one ERC-721 token id right now (ownerOf)') and explicitly distinguishes itself from arb_nft_balance and arb_nft_metadata, which cover token counts and metadata respectively.

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?

Gives concrete when-to-use triggers (verify holder before a trade, mint gate, airdrop) and names both alternatives with their scope for count and metadata, so the agent can choose without opening other schemas.

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