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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds genuinely useful context beyond them: pay-per-call pricing ($0.003), that the return value is a paid x402 request URL with schema and example, that invalid input is rejected before charging, and that a P0 key makes it auto-pay and deduct. That is meaningful added disclosure for a paid read, though it says nothing about latency, pagination or freshness of balances.

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-loaded with the use condition, then scope, then routing alternatives, then payment mechanics — a sensible ordering. It is dense but every clause carries information; only the long key-purchase URL is mildly noisy, and the payment explanation runs a bit long.

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 with no output schema, the description covers what is returned (an x402 request URL plus response schema and example), the cost, the error/charge behavior, and the auth upgrade path. Combined with annotations that carry the safety profile, an agent has everything needed to call and consume 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% and both parameters are documented there (chains as a comma list with default of all EVM chains, address as 0x or ENS). The description's only added signal is the enumeration of supported chains and tokens, which is useful scoping but does not enrich the parameter syntax or format beyond the schema. Baseline 3 applies.

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 (wallet token balances) plus scope: multiple chains, one wallet, with an explicit token list (native, USDC, USDT, DAI, WETH, WBTC/cbBTC). It names the exact siblings it is not (evm_erc20_balance, evm_native_balance, wallet_balance_batch), so an agent can route without opening any 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?

Opens with an explicit when-to-use condition (several chains in one call) and enumerates the alternatives with their selecting conditions: one token/one chain -> evm_erc20_balance, native/one chain -> evm_native_balance, many wallets -> wallet_balance_batch. Nothing is left to inference.

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