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

Goes well beyond the annotations by disclosing error semantics (no contract returns 404, non-ERC-20 contract 422, both uncharged), pricing model ($0.01/call via x402 USDC or card key, first 25 free, failed calls free), and that it reads/computes only with each call charged. This clarifies exactly why idempotentHint=false is set.

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 with what it returns, then usage, then input constraints, then error/pricing behavior. The pricing and free-tier sentences are dense but relevant to cost-aware agents; the sentence count is near the upper bound for a two-parameter tool.

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 nonetheless enumerates the returned fields (raw amount, decimals, symbol, human-readable amount) and covers error cases and billing. An agent has everything needed to call it and interpret the result.

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 both parameters are already documented; the description adds a useful format constraint that both inputs must be 0x addresses of 40 hex characters and reinforces that 'token' accepts a ticker or contract address. That is a modest but real addition over the schema text.

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: ERC-20 token balance of a wallet on Avalanche via balanceOf, with enumerated return fields. It explicitly distinguishes itself from the native-coin sibling ('for the native coin use avax_balance'), so an agent can route between the two without opening schemas.

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 a concrete usage context ('check stablecoin or token holdings before a transfer or trade') and names the alternative for the native coin case. It does not address the reverse case (when NOT to use this, e.g. use avax_allowance for approvals or avax_token_info for metadata), which keeps it short of a 5.

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