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

Annotations already cover read-only and non-destructive, but the description goes further: 404 for a missing contract, 422 for a nonexistent token id, and both uncharged, plus pricing ($0.01/call via x402 USDC or card key, first 25 free, failed calls free) and the non-idempotent billing implication ('each call is charged, so repeats are not free'). That is strong behavior beyond the annotations, though it stops short of describing response shape or latency.

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?

Front-loaded with the definition, then scenario, then alternatives, then errors, then pricing. Dense but nearly every clause carries information; the pricing/charging sentence is slightly repetitive ('each call is charged, so repeats are not free' after already listing price).

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 two-param read tool with no output schema, the description covers what is returned (owner address, collection name and symbol), failure modes with status codes, and billing. An agent has everything needed to call it correctly and interpret failures.

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 baseline is 3; the description adds a worked example with a real 0x contract address and tokenId=1 that clarifies the expected formats and pairing. It does not explain edge cases like non-numeric tokenIds tolerated by the schema's union type.

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 specific verb and resource: 'the wallet that holds one ERC-721 token id right now (ownerOf), plus the collection's name and symbol.' It also names the two adjacent siblings (unichain_nft_balance, unichain_nft_metadata) so the agent can discriminate without opening schemas.

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?

Explicit when-to-use scenarios ('verify who holds an NFT before a trade, a mint gate or an airdrop') and explicit routing for the two nearest alternative tools by name. Nothing is left to inference.

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