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

Goes well beyond the annotations: discloses live-on-chain sourcing, the uncharged 422 failure mode, and full billing mechanics ($0.01/call via x402 or card key, first 25 free, failures free). The line 'each call is charged, so repeats are not free' reconciles the idempotentHint=false annotation, which would otherwise look odd for a pure read.

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 returned fields and the sibling exclusion, so the important routing signal comes first. The billing information is somewhat repetitive ('failed calls free' and 'each call is charged' restate the same pricing tier twice), costing a bit of tightness.

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?

Although no output schema exists, the description enumerates the returned fields, which is the equivalent disclosure. Combined with the failure mode, input formats, and cost model, an agent has everything needed to call it correctly and predict the result shape.

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 already 100%, and the description reinforces the ticker-or-address duality plus a concrete worked address example (USDC). It also attaches error semantics to the parameter for the non-contract case. It adds value, but most of the parameter meaning is duplicated from the schema rather than extended.

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 enumerates exactly what is returned (name, symbol, decimals, total supply) for a specific resource (ERC-20 contract on Ethereum). It explicitly distinguishes itself from the sibling eth_token_balance, so an agent can route without opening a schema.

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?

Gives two concrete use cases ('identify an unknown token address' and 'format raw amounts') and an explicit exclusion with the named alternative ('for a holder's balance use eth_token_balance'). The 422-for-non-ERC-20 note tells the agent when the call will fail rather than return data.

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