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

Goes well beyond annotations: explains the non-obvious readOnlyHint=false (reads only, but charged per call), gives the 422-on-non-ERC-20 error with 'uncharged' semantics, and states pricing, free tier, and that failed calls are free. This is exactly the context annotations cannot carry.

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 purpose and fields, then usage routing, then input/error behavior, then cost. Every sentence carries distinct, necessary information with no filler.

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 still names the returned fields (name, symbol, decimals, total supply), plus error and pricing behavior. Nothing needed 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%, so the baseline is 3, but the description adds the concrete 0x example address and the failure semantics for a non-ERC-20 address, both of which meaningfully extend the schema's terse '0x ERC-20 token contract address'.

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 (look up) and resource (ERC-20 name, symbol, decimals, total supply) read live from the contract. Immediately distinguishes itself from eth_token_balance by naming it, and identifies the input as the token contract address.

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?

Explicitly gives both when-to-use (identify an unknown token address, format raw amounts) and when-not (holder balance → eth_token_balance). The routing condition between the two siblings is unambiguous.

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