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

Annotations already declare read-only, idempotent and open-world behavior, so the description isn't burdened with safety. It still adds real context the annotations don't: the price of $0.005 USDC per call via x402 on eip155:8453, and the fact that values are read at the latest block, which tells the agent about freshness.

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 compact sentences with the purpose front-loaded, followed by output shape and pricing. Dense but nothing is wasted, though the parenthetical about decimals/symbol makes the second sentence heavy.

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 usefully discloses the return shape (raw plus formatted values with decimals and symbol) and the billing cost. It stops short of covering failure modes such as unsupported chains or invalid token addresses, which matters for a paid, open-world call.

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 67% and already documents chain options and the tokens array. The description adds the useful cap of 'up to 10 ERC-20 tokens' and clarifies that the chain is user-chosen, but says nothing about the required address format or the string-vs-array flexibility of tokens.

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 states a specific verb+resource: reading native coin and ERC-20 token balances for a given address on a chosen chain. That is clearly distinct from siblings like evm_token or evm_contract by resource type, 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 (you need balances for an address, so call this), but there is no explicit when-to-use/when-not guidance, no mention of prerequisites beyond payment, and no pointer to an alternative such as evm_token for token metadata.

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