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

Annotations already cover read-only, non-destructive, non-idempotent and open-world hints, yet the description still adds real value: live-on-chain reads, the 422 error path for non-ERC-20 contracts, that failures are free, and the $0.01/call billing model with the 25-free-call allowance. The statement that repeats cost money is consistent with idempotentHint=false. It stops short of describing latency or rate limits, which keeps it from a 5.

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, then usage routing, then input format, then billing caveats — a sensible order with no filler sentences. It is on the dense side (billing and example occupy a third of the text), but every clause conveys something an agent would otherwise have to guess.

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?

There is no output schema, and the description compensates by enumerating the returned fields (name, symbol, decimals, total supply). For a single-parameter, read-only lookup, the error path, cost model and input format are all present, leaving nothing an agent needs in order to call it correctly.

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 property description already explains the ticker-or-address input, so baseline is 3. The tool description earns above baseline by adding concrete ticker examples (USDC, WETH), a full worked address example, and the failure semantics for a valid-but-non-ERC-20 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?

Opens with a specific verb and resource ('Look up the name, symbol, decimals and total supply of an ERC-20 token contract on Ethereum') and even states the four returned fields. It explicitly distinguishes itself from the sibling eth_token_balance, so an agent can route between them without opening either 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', 'format raw amounts') and names the alternative with its condition ('for a holder's balance use eth_token_balance'). It also states when the tool will not help: a non-ERC-20 address returns 422 uncharged.

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