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

Beyond the readOnly/destructive annotations it discloses pricing ($0.01/call, first 25 free), that failed and malformed-address calls are free (400, uncharged), that repeats are billed, and that the read is at the latest block only. This adds materially to what annotations convey.

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-loads purpose, units and block scope, then alternatives, then error/cost behavior. Dense but nearly every sentence carries information; the pricing/credits clause is long and slightly interrupts the usage flow but is not 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 supplies the return shape (wei and S), the block semantics, error behavior, and cost model. There is no remaining gap an agent needs filled before calling it.

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; the description still adds that any wallet or contract address is accepted, supplies an example format, and explains the 400 rejection for malformed input. Marginal extra value over the schema's own parameter description.

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 S balance ... of any 0x wallet address on Sonic at the latest block'), includes the underlying RPC method and units, and explicitly distinguishes itself from sonic_token_balance (ERC-20) and wallet_portfolio (all holdings). An agent can pick it 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 a concrete use case ('check whether a wallet can pay gas or a transfer') and names both alternatives plus the condition that selects each. This is explicit when-to-use and when-not-to-use routing.

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