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

Annotations already cover the safety profile (readOnlyHint, openWorldHint, destructiveHint=false), but the description adds behavior they do not: partial-failure handling ('a network whose nodes do not answer is listed with an error instead of failing the call') and the billing model ($0.005/call via x402 USDC or card key, first 25 free, failed calls free), which explains why idempotentHint=false matters — repeats cost money. This is materially useful context beyond the structured fields.

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 correctly: purpose and scope first, routing guidance second, failure semantics third, example and pricing last. Every sentence carries information, though the dense pricing/credits clause is the one stretch that could be trimmed without losing agent-relevant meaning.

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?

There is no output schema, and the description compensates by describing the return shape (per-network native + USDC balances, a USDC total, per-network error entries). With annotations covering safety and open-world behavior and a single fully-documented parameter, this is close to complete; a note on whether the USDC total excludes errored networks would close the last gap.

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?

There is exactly one parameter and schema coverage is 100% ('0x wallet address'), so the schema already carries the semantics. The description adds only a concrete example address, which illustrates format but conveys no new constraint 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?

States a specific verb and resource ('read a wallet's native coin and USDC balances') plus the exact scope (Base, Ethereum, Arbitrum, Optimism, Polygon, plus a USDC total), and explicitly distinguishes itself from <chain>_token_balance and wallet_portfolio. An agent can pick it out of a 150+ sibling list without opening a 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?

Gives an explicit when-to-use ('find where a wallet's funds are before a payment or bridge') and names two alternatives with the exact conditions that select them: one token on one network -> <chain>_token_balance, all tokens on Base -> wallet_portfolio. 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.