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

Annotations already cover safety (readOnlyHint, destructiveHint false, openWorldHint), but the description adds real operational detail beyond them: strings over 1,000 characters such as on-chain SVGs are truncated, a nonexistent token is 422 and uncharged, unreachable metadata surfaces as metadataError, and each call is billed so repeats are not free — which concretely explains idempotentHint=false.

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 return shape are front-loaded, and nearly every sentence contributes a fact. It runs long with pricing, repeat-charge, and free-tier detail at the tail, which is relevant but could be trimmed for readers who only need invocation guidance.

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?

With no output schema, the description fully carries the burden: it describes the resolved field set, the truncation of large values, the two distinct failure modes (422 nonexistent vs. metadataError unreachable), and the cost model. An agent needs nothing else to call it correctly or interpret results.

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 schema already defines both parameters; the description nonetheless adds a concrete example pair (0xC36442b4a4522E871399CD717aBDD847Ab11FE88, tokenId=1) and reinforces that the contract is an ERC-721 collection address whose id is being queried. Useful, but modest value over an already complete schema.

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 the specific resource (the tokenURI of one ERC-721 token id and the JSON it resolves to) and enumerates the fields returned (name, description, image, attributes). It is unambiguously distinguishable from eth_nft_owner, which it names explicitly.

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?

"Use to show or check what an NFT is; for its owner use eth_nft_owner" states both the intended use and the alternative tool that covers the adjacent need. Supported URI schemes (data:, https, ipfs:// via ipfs.io) further bound when this tool applies.

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