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

Adds real context beyond the annotations: freshness (latest block, read live), what is returned (wei and ETH), and the paid-call model ($0.001 USDC on Base via x402, charged per successful call). Note the tension with readOnlyHint=false, though the disclosed per-call payment plausibly explains why the invocation is annotated as non-read-only while the underlying chain access is a pure 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?

Two tight sentences, front-loaded with what is returned and from where, then the usage context and cost. Every clause carries information; nothing is redundant or padded.

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 ETH), the chain and freshness semantics, and the payment requirement — everything an agent needs to decide and call correctly. Nothing material is missing for a single-parameter read tool.

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?

Only one parameter, and the schema already documents it at 100% coverage ('0x wallet or contract address'). The description's 'any address on Arbitrum One' reinforces the accepted input but adds no syntax, validation, or format detail beyond the schema — baseline 3.

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 concrete verb+resource with full scope: native ETH balance of any address on Arbitrum One, returned in wei and ETH, read live at the latest block. This cleanly separates it from siblings like arb_token-balance (ERC-20 vs native) and eth_balance/base_balance (different chains) without needing to open a 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 clear triggering context: check whether a wallet is funded before sending, paying gas, or settling. It stops short of naming alternatives (e.g., use arb_token-balance when the asset is an ERC-20 rather than native ETH), which would matter given the very large sibling set.

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