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

Annotations already cover the safety profile (readOnlyHint true, destructiveHint false, openWorldHint true), and the description goes further by disclosing cost behavior: $0.01/call via x402 USDC or a card key, first 25 free, failed calls free, and that repeats are not free, which explains the idempotentHint=false flag. It does not describe pagination or response shape, but neither applies to a single-value 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?

Purpose, units, alternatives, error behavior and pricing are front-loaded in three tight sentences with no filler. The pricing and free-tier detail is dense but earns its place because it explains the non-idempotent, per-call-charged behavior.

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 single-parameter read with no output schema, the description covers everything an agent needs: what is returned and in which units, the block height used, invalid-input handling, cost model, and the alternatives for token or multi-asset queries. Nothing material 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% and there is only one parameter, so the schema already carries the baseline. The description still adds value by showing a concrete example address and confirming that any 0x wallet or contract address is acceptable while a malformed one returns 400, which the schema does not say.

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 (returns the native ETH balance of a 0x address on Linea via eth_getBalance at the latest block), and declares both output units (wei and ETH). It explicitly distinguishes itself from linea_token_balance and wallet_portfolio, so the agent can separate it from the many sibling *_balance tools without opening schemas.

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 a concrete use case (check whether a wallet can pay gas or a transfer) and names the alternatives with the condition that selects them: linea_token_balance for ERC-20, wallet_portfolio for all holdings at once. It also states what happens on bad input (400, uncharged), leaving nothing to inference.

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