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

Goes well beyond annotations by disclosing error semantics (404 for missing contract, 422 for non-ERC-721, both uncharged), pricing ($0.01/call via x402 or card key, first 25 free, failed calls free), and that repeats are billable — which is the practical meaning of idempotentHint=false. It also states the tool changes nothing, consistent with readOnlyHint=true.

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?

Core semantics come first, then the sibling routing, then error and billing details. The final two clauses about payment and idempotency are dense but each carries distinct operational information; slightly compressed phrasing keeps it from a 5.

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 correctly tells the agent what comes back (count plus collection name and symbol), supplies failure codes, and warns about per-call billing. Nothing an agent needs to call this 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%, so both parameters are already documented as 0x addresses. The description's note that both inputs are 0x addresses duplicates the schema, and adds only the ordering-free clarification that contract is the collection and address the wallet — which the schema already states. Baseline 3 applies.

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: how many NFTs of one ERC-721 collection a wallet holds on Unichain, implemented as balanceOf, plus the side output of collection name and symbol. It explicitly differentiates from the nearest sibling (unichain_nft_owner) and from unichain_token_balance by scoping to ERC-721.

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?

Names two concrete use cases (gate check before a token-gated action, verifying a wallet still holds a collection) and routes the agent to unichain_nft_owner for the one-token-id question. When-to-use and the alternative are both explicit.

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