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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds the cost detail ($0.005 USDC via x402), which is valuable behavioral context beyond the annotations. It doesn't describe return format, but for a simple balance check this is acceptable.

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 with zero waste. The core purpose is front-loaded, and the cost detail is a single additional sentence. Every word earns its place.

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 balance check with one fully-documented parameter and annotations covering safety, the description is nearly complete. The cost disclosure is a nice addition. The only minor gap is not describing the return format, but for a balance tool this is easily inferred.

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 description coverage is 100%, so the schema already fully documents the address parameter. The description doesn't add parameter-level detail beyond what the schema provides, but the baseline of 3 is appropriate since the schema does the heavy lifting.

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 verb 'Check' and the specific resource: native ETH balance of a wallet or address on Base mainnet. It also distinguishes itself from sibling tools like base_erc20_balance by specifying 'native ETH balance'.

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 clearly states the context for use: checking native ETH balance on Base mainnet. It doesn't explicitly mention when not to use it or name alternatives, but the context is clear enough given the sibling list includes base_erc20_balance for token balances.

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