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

Annotations already declare read-only, idempotent, and non-destructive behavior. The description adds meaningful context beyond this, such as the testnet nature of Arbitrum Sepolia, the role of MockUSDC in settling subscriptions and fact-oracle queries, and the exclusion of Base-mainnet balances. This helps the agent understand the operational context and constraints.

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?

The description is concise and well-structured: two sentences, with the main action front-loaded in the first sentence and critical clarification in the second. Every sentence adds value without redundancy.

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 simple read-only tool with one parameter and an existing output schema, this description is highly complete. It specifies the exact tokens, network, the address scope, and explicitly mentions what it does not include, providing sufficient context for correct tool selection.

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?

The input schema provides 100% coverage for the single 'address' parameter with a clear description ('Ethereum address (0x...)'). The tool description adds no additional parameter-specific information, so baseline 3 is appropriate since the schema carries the semantic weight.

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 clearly states the tool's function: getting USDC and ETH balances for an address on Arbitrum Sepolia. It specifically names the tokens and network, and distinguishes from sibling tool byte_buy_data by explicitly stating what it does NOT show, making the purpose unambiguous.

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?

The description provides clear context for when to use this tool: when checking USDC/ETH balances on Arbitrum Sepolia, and it explicitly notes it does not show Base-mainnet USDC spent by byte_buy_data. This implies the alternative for Base-mainnet balances but does not explicitly say 'use byte_buy_data for that', so it is not a full when-to-use guide.

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