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

Annotations (readOnlyHint=false, openWorldHint=true) are sparse, so the description carries real weight and delivers: it discloses live on-chain reading, the $0.001 USDC per successful call cost, and the x402 payment mechanism — all things the annotations do not convey. It omits what happens on failure (e.g., whether failed calls are charged) and any wallet/x402 setup prerequisite, keeping 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?

Three tight sentences: what it returns, when to use it, and the cost. Return-field enumeration is front-loaded and earns its place given there is no output schema, though the sentence carries a slightly dense clause chain.

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 correctly compensates by naming the return shape (raw amount, decimals, symbol, human-readable amount). Cost, payment method, and chain are all present; only error/failure semantics and any x402 setup requirement are 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 description coverage is 100% for both parameters ('0x ERC-20 token contract address', '0x wallet address'), so the schema already documents them. The description adds no parameter-level detail (no address format nuance, no checksum guidance), which is the expected baseline 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+resource with chain scoping: 'ERC-20 token balance of a wallet on Arbitrum One', and enumerates the returned fields. This cleanly separates it from the many sibling chain variants (eth_token_balance, base_token_balance, op_token_balance, polygon_token_balance).

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 usage context: 'Use to check stablecoin or token holdings before a transfer, payment or trade.' It does not name an alternative tooling path or state exclusions (e.g., when to use arb_balance instead for native ETH), so it stops short of explicit alternatives.

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