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

Beyond the readOnly/destructive annotations it discloses block semantics (latest block), return units (wei and POL), error behavior (malformed address returns 400 and is uncharged), and pricing ($0.002/call, first 25 free, failed calls free). The line 'each call is charged, so repeats are not free' also explains the non-obvious idempotentHint=false, which annotations alone would leave puzzling for a read-only tool.

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 what the tool returns and at what block, then routing, then error and cost semantics, in one tight paragraph. Each clause carries distinct information, including the pricing details that no structured field conveys.

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 tool with no output schema, the description covers units, block freshness, error handling, cost, and sibling routing. Nothing an agent needs to invoke it correctly or interpret the result 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 the single parameter is already described as a 0x wallet or contract address, so the baseline is 3. The description adds a worked example address and the rejection consequence for malformed input, giving slightly more than the schema alone, though it does not clarify contract-vs-wallet address behavior.

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 POL balance (eth_getBalance) of a 0x address on Polygon PoS at the latest block, returned in wei and POL. It explicitly separates itself from polygon_token_balance (ERC-20) and wallet_portfolio (all holdings), so an agent can pick it without opening another 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 when-to-use ('check whether a wallet can pay gas or a transfer') and names two alternative tools with the conditions that select them (ERC-20 tokens, all holdings at once). Exclusions and alternatives are both explicit.

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