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

Annotations already carry the safety profile (readOnlyHint=false, openWorldHint=true, idempotentHint=false, destructiveHint=false). The description adds meaningful context beyond them: freshness ('latest block') and the billing behavior ('$0.001 in USDC on Base per successful call, paid with x402'), which explains the non-read-only annotation and the cost/auth requirement. It does not cover failure modes or rate limits, so not 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?

Three tight sentences, front-loaded with what it does, then when to use it, then cost. Every sentence earns its place with no redundancy.

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 one-parameter read with no output schema, the description is nearly complete: it names the return units ('in wei and in ETH'), the data source, usage context and pricing. It omits any error/empty-address behavior, which keeps it from a 5.

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% for the single 'address' parameter, so the schema already documents it. The description adds no format or constraint detail beyond 'any address'. Baseline 3 is correct when the schema does the heavy lifting.

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 and resource ('Native ETH balance of any address on Ethereum') and pins down the chain and data source ('read live from the chain at the latest block'). It distinguishes itself from siblings like eth_token-balance and eth_nonce, and from the same-named tools on other chains (base_balance, arb_balance). An agent can route correctly without opening the 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 explicit when-to-use context: 'check whether a wallet is funded before sending, paying gas or settling.' That is a concrete trigger for selecting this over eth_token-balance or eth_nonce. It does not name alternatives or exclusions explicitly, so it stops short of a 5.

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