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

Annotations already declare readOnlyHint=true, and the description adds valuable behavioral detail: it discloses the exact contract calls (balanceOf, decimals, symbol) and the return format (raw, formatted, symbol). This context helps the agent anticipate that the token must implement these methods and that duplicate calls may occur, going beyond the annotation's basic safety declaration.

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 three concise sentences, front-loaded with the core purpose, followed by return values and underlying contract calls. Every sentence adds value with no redundancy or fluff, making it easy to parse quickly.

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 simple read-only tool with no output schema, the description is complete: it covers the network (Ethereum mainnet), asset type (ERC-20), the two parameters, the return values, and the underlying contract interactions. No critical context is missing for correct use.

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 description coverage is 100% with both parameters well-defined ('ERC-20 token contract address' and 'Wallet address to check balance for'). The description reinforces this but does not add significant new meaning beyond what the schema provides. Baseline 3 is appropriate given full schema coverage.

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 clearly states the tool's purpose: 'Get ERC-20 token balance for a wallet address on Ethereum mainnet.' This specific verb+resource+scope immediately distinguishes it from similar tools like eth_get_balance (native ETH) and mezo_get_token_balance (different chain). It also lists what it returns, reinforcing the purpose.

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 description provides clear context by specifying Ethereum mainnet and ERC-20 tokens, which implies it is not for native ETH or testnets. It does not explicitly name alternatives or exclusions, but the context is strong enough to guide selection. A 4 is appropriate for clear context without explicit when-not guidance.

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