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

Beyond the readOnly/idempotent annotations, it discloses the non-obvious mechanics: the default response is the exact paid x402 request (GET /wallet/balance, $0.003 per call) that must be called with an x402/MPP client, and that a P0 Bearer key makes the tool perform the paid call itself. It also covers failure behavior (rejected input is not charged), which annotations cannot express.

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?

It is front-loaded with the 'use when' condition, which is good, but one dense paragraph carries usage, output format, pricing, error behavior, alternatives, and auth/key-purchase instructions, with some redundancy ('One wallet across several chains' restates the opening clause). The key-purchase URL in particular adds bulk an agent rarely needs mid-call.

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 tool with no output schema, a two-parameter schema that is fully documented, and a paid-call wrapper, the description covers everything an agent needs: what it returns, the cost, that the returned payload is a request to be executed, and the access-key shortcut. No material gap remains.

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 already 100%, and the description adds meaning the schema lacks by enumerating the token set covered (native, USDC, USDT, DAI, WETH, WBTC/cbBTC) and reiterating the single-wallet/several-chain scoping of `address` and `chains`. It does not add syntax detail beyond the schema's existing 'comma list' guidance.

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 uses a specific verb and resource (return a wallet's token balances across several named chains and named tokens) and explicitly carves out the sibling cases: evm_erc20_balance for one token on one chain, evm_native_balance for the native coin, wallet_balance_batch for many wallets. An agent can route correctly 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?

It gives an explicit 'use when' trigger (one wallet, several chains, one call) plus three named alternatives with the exact conditions that select them. It also states the input-validation precondition ('bad input is refused before any charge'), which is actionable guidance rather than inference.

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