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

Goes well beyond the annotations: it explains the non-obvious readOnlyHint=false ('not marked read-only because each call is charged'), discloses failure semantics with HTTP codes (404 no contract, 422 non-ERC-20), confirms failed calls are uncharged, and states pricing ($0.003/call, first 25 free, x402 or card key). This directly resolves the one annotation an agent would otherwise misread.

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 purpose and return shape, then usage, then error/pricing detail in descending order of importance; every clause carries information. The pricing and free-tier sentences are somewhat dense, but they are decision-relevant for an agent weighing a paid call.

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?

There is no output schema, and the description compensates by naming the returned fields (raw amount, decimals, symbol, human-readable amount). Combined with error codes, cost semantics, and the parameter format constraint, nothing an agent needs to invoke this correctly is missing.

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 already 100%, so the baseline is 3, but the description adds a real constraint not in the schema: both inputs must be 0x addresses of exactly 40 hex characters. It does not, however, clarify which argument is the token versus the wallet beyond what the schema's own property descriptions say.

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 precise verb and resource ('Read one wallet's balance of one ERC-20 token on Ethereum') and enumerates the returned fields. It explicitly distinguishes itself from the closest sibling by naming eth_balance as the tool for the native coin, so an agent can route correctly without opening either 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 operative use case ('check stablecoin or token holdings before a transfer or trade') and an explicit alternative for the adjacent case ('for the native coin use eth_balance'). The when-to-use and the sibling-deflection rule are both stated outright.

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