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

Annotations already state readOnlyHint=true and destructiveHint=false, but the description adds meaningful context beyond them: a missing contract returns 404, a nonexistent token returns 422, both failed cases are uncharged, and each successful call costs $0.01 with the first 25 free. It also clarifies that repeated calls are not free because every call is charged, which directly supports the non-idempotent behavior.

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 dense but front-loaded: purpose first, then usage guidance, alternatives, error behavior, an example, pricing, and safety. Every sentence adds operational value, and none of the detail repeats structured fields without adding context.

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, but the description explains what is returned: the current owner plus collection name and symbol. It also covers prerequisites, error outcomes, billing behavior, and the read-only nature of the call, leaving nothing essential for correct invocation missing.

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 the required contract address and numeric tokenId. The description provides a concrete example using both parameters, but it does not add format or edge-case semantics beyond what the schema states.

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 names a specific verb and resource: it returns the wallet that currently holds one ERC-721 token id (ownerOf), plus the collection name and symbol. It clearly distinguishes the tool from polygon_nft_balance and polygon_nft_metadata, so an agent can identify its exact scope 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?

It gives explicit usage contexts: verifying who holds an NFT before a trade, a mint gate, or an airdrop. It also names the alternative tools and the conditions that select them: polygon_nft_balance for counts and polygon_nft_metadata for metadata.

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