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

Goes well beyond the readOnlyHint/openWorldHint annotations with critical behavior an agent cannot infer: cost of $0.002 USDC per call, x402 payment gating, that unpaid calls return PaymentRequired, and that x402 MCP clients pay automatically. This is exactly the kind of paid-endpoint context the annotation set cannot convey.

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 sentences, zero waste, with the capability front-loaded and the payment mechanics second. Each sentence carries distinct information (scope + cost/gating).

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 one-param, read-only, no-output-schema tool, the description covers the essential context: what data, which chains, and the payment flow. Minor gaps remain around the return shape (e.g., whether native balance means ETH and how per-chain results are keyed).

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?

One parameter with 0% schema description coverage; the schema's regex conveys the 0x address format. The description only says 'one address', adding nothing about whether the same address is used on both chains or what else identifies it, so it does not compensate for the coverage gap.

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 (USDC and native balance) with explicit scope: one address across two named chains (Base and Arc) in one call. This clearly separates it from the broader address_profile sibling, though no 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?

Usage is implied by the scope statement (use when you need balances only, on Base/Arc), but there is no explicit when-to-use/when-not or reference to address_profile as the alternative for broader data. The payment note clarifies a precondition rather than a selection rule.

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