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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, covering the safety profile. The description adds valuable context beyond annotations: it mentions the cost ($0.001 USDC per call), the supported chains, and the byte-identical REST endpoint. It does not discuss error behavior (e.g., if the token doesn't exist), but for a simple read tool this is a minor omission. It does not contradict the 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?

The description is three concise sentences, each serving a purpose: the first states what the tool does, the second gives the cost, and the third lists chains and the exact endpoint. It is front-loaded with the core purpose and contains no filler or redundant text. This is an exemplar of conciseness.

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?

Given that the tool has an output schema (not shown but present) and annotations cover safety, the description is fairly complete. It includes the cost, supported chains, and the exact REST endpoint for reference. It doesn't mention potential error cases (e.g., invalid token ID, non-existent NFT) or any rate limits, but for a simple ownership query this is a minor gap. The agent has enough information to call it correctly and understand the result.

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?

The schema describes all three parameters (chain, token, tokenId) with 100% coverage, so the description doesn't need to add much. The description includes an example URL that implicitly shows the parameter format (chain, token address, tokenId) and the allowed chain values. However, it doesn't add new semantics beyond the schema—it just reinforces what the schema already states. 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?

The description explicitly states 'ownerOf(tokenId) resolved for one NFT — proof of who holds a specific id right now, from the contract itself.' This clearly identifies the operation (resolving owner), the resource (a single NFT token id), and differentiates it from sibling tools like chain_nft_balance or chain_nft_owner_at by emphasizing 'right now' and 'from the contract itself.' The purpose is unambiguous.

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 provides useful context such as cost, supported chains, and an exact endpoint reference, but it does not explicitly say when to use this tool over alternatives like chain_nft_owner_at (likely historical ownership) or chain_nft_balance (count of NFTs). The phrase 'right now' implies current state, but there is no direct 'use this for X, use that for Y' guidance. This leaves some inference to the agent.

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