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

With no annotations, the description carries the full burden and does disclose real behavior: data is read live from Arbitrum One, results are formatted with symbol and decimals, and the call costs $0.005 USDC on Base via x402 — a payment prerequisite an agent must know before calling. It stops short of describing failure modes for invalid token addresses or whether the ETH entry is always included.

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?

A single dense sentence covering scope, chain, limit, formatting, and freshness, followed by the cost clause. The most decision-relevant information (what it returns, on which chain) is front-loaded with no 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?

For a two-parameter read tool with no output schema and no annotations, the description covers return content (ETH plus token balances with symbol/decimals), chain, limits, and the x402 payment requirement. Only the shape of the returned data and error conditions are left thin, which is a minor gap at this complexity.

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 both parameters are already documented in the schema. The description only restates the 20-token cap and the fact that ETH is always included alongside the listed tokens, adding marginal meaning beyond the schema. Baseline 3 is appropriate.

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?

The description gives a specific verb+resource: reads native ETH balance plus up to 20 listed ERC-20 token balances on Arbitrum One, live. It implicitly distinguishes itself from the base/eth/optimism/polygon siblings by naming the chain, but it never contrasts with arbitrum_wallet_profile or arbitrum_token_snapshot, which are the nearest overlapping siblings.

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?

'Tokens you list' implies the caller must supply contract addresses and that unlisted tokens are not returned, which is usable context. There is no explicit statement of when to prefer this over arbitrum_wallet_profile or arbitrum_token_snapshot, and no prerequisites beyond the cost note.

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