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

With annotations only declaring readOnly/openWorld, the description carries the operationally important details: a 5-second metadata timeout, a 256 KB cap, failure surfaced via metadataNote rather than a thrown error, and $0.002 USDC charged via x402 only on success. That is exactly the 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?

Three sentences, each with a distinct job: what is returned, failure/cap semantics, then pricing. Well front-loaded with no filler, though the return-value enumeration slightly overlaps the output schema.

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?

For a paid, read-only, open-world lookup, all decision-relevant facts are present: inputs documented by schema, outputs enumerated, failure semantics, timeout/size limits, and cost/charge policy. Nothing an agent needs to call it correctly is 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 coverage is 100% and the schema already documents chain (default base), tokenId (decimal string) and contract (0x…). The description adds no additional parameter semantics such as chain aliasing, tokenId formats beyond decimal, or contract validation behavior, so it sits at the baseline.

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?

States a precise verb+resource: 'ERC-721 facts for one token', enumerating exactly what is returned (owner, collection name/symbol, tokenURI, metadata). The ERC-721 scoping cleanly distinguishes it from ERC-20/generic siblings like evm_token, evm_contract and token_metadata.

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 conditional 'metadata when the URI is http(s) or ipfs' implies when metadata retrieval happens, which is useful usage context. However, it never states when to choose this tool over the many nearby siblings (evm_contract, evm_token, token_metadata, rpc_evm), so the agent must infer routing.

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