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

With no annotations, the description carries the full burden and does: it discloses the exact return shape (raw integer string, decimals, formatted amount, symbol), that no API key or account is needed, and the $0.005 per-call cost paid over x402 in USDC. Pre-payment and auth requirements are exactly the behavioral context an agent needs before invoking.

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 usage trigger is front-loaded and every clause carries information (return fields, exclusions, pricing). The main sentence is dense and runs long, which slightly hurts scannability, but there is no filler.

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?

Return values, cost, auth model, and sibling routing are all covered, which is more than enough for a 3-parameter read tool with no output schema. The only gap is the chain parameter's optionality and default chain, left unaddressed.

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 100%, so address and token are already documented as 'Wallet to look up' and 'ERC20 contract address'. The description reinforces 'any address for any token' but adds nothing about the optional chain parameter or its default, so it stays at the baseline.

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 — 'the ERC-20 balance of any address for any token' — and explicitly names what it is not (native coin balance, allowance). An agent can separate it from evm_balance and evm_erc20_allowance 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 the triggering condition ('confirm a wallet holds enough of a token before it swaps, pays or settles') and two explicit exclusions with the sibling endpoints to use instead. When-to-use and when-not-to-use are both stated.

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