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

Beyond annotations, the description discloses error behavior (404 for missing contract, 422 for non-ERC-721), that failed calls are uncharged, and pricing ($0.01/call, first 25 free). It also clarifies the tool only reads/computes and changes nothing, while noting repeats are charged.

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 front-loaded with purpose and usage, then includes errors and pricing in a compact flow. It is somewhat dense with operational details, but each sentence largely earns its place.

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-parameter read-only tool with no output schema, the description covers purpose, return content (balance plus collection name and symbol), error cases, and charging behavior. An agent has enough information to call it correctly and interpret outcomes.

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 both inputs as 0x wallet and 0x ERC-721 contract addresses. The description reinforces that both inputs are 0x addresses but adds little semantic detail beyond the schema, which is the expected baseline when schema coverage is high.

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 states a specific verb and resource: how many NFTs of one ERC-721 collection a wallet holds on Ethereum (balanceOf), plus the collection name and symbol. It explicitly distinguishes itself from the sibling eth_nft_owner, which covers who holds one token id.

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 concrete when-to-use cases: checking a holder before a token-gated action or seeing whether a wallet still holds a collection. It also names the alternative eth_nft_owner and the condition for choosing it.

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