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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description adds genuinely useful context annotations cannot: the $0.005 USDC per-call cost and the x402 payment endpoint, which affects whether an agent can call it at all.

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 short sentences plus a pricing note, with the core purpose front-loaded. No filler, though the pricing detail is tucked in a trailing parenthetical rather than surfaced as a callability constraint.

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 leaves the return shape undefined — a decimal USDC amount, raw base units, or a per-account breakdown? It also doesn't say what happens when the wallet has zero USDC token accounts. Adequate for selection, incomplete for interpretation.

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%, with both 'address' and 'payment' documented in the schema itself, so baseline is 3. The description adds nothing about parameter behavior (e.g., what happens with an invalid base58 address or when the payment header is omitted) beyond what the schema states.

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 resource and scope: "USDC balance of a Solana wallet (sum of all USDC token accounts)." The parenthetical distinguishes it from solana_token_balances (per-token listing) and solana_sol_balance (native SOL), though neither sibling is named explicitly.

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?

"Useful before paying or invoicing an agent" gives one implied use case but no when-not guidance and no routing to alternatives such as solana_token_balances for other SPL tokens or wallet_portfolio for a full picture.

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