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

Annotations already declare read-only/non-destructive, but the description adds substantial context they don't carry: pricing ($0.01/call via x402 or card key, first 25 free, failed calls free), the fact that repeat calls are charged (consistent with idempotentHint=false), that values are read live from the contract, and the status codes for two failure modes. Nothing contradicts the annotations.

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, and tightly packed. The pricing/free-tier sentence is longer than strictly needed for invocation but is genuinely useful information; only minor trimming would improve it.

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, yet the description fully specifies the return fields, chain scope, input formats, cost model, and error behavior — everything an agent needs to call it correctly 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, making 3 the baseline. The description partially adds value by specifying 0x / 40-hex input format, but it says "Both inputs are 0x addresses," which conflicts with the token parameter accepting tickers like USDC — a small inconsistency that reduces the net value added.

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 — ERC-20 balance of a wallet via balanceOf — and enumerates the exact returned fields (raw amount, decimals, symbol, human-readable amount). It also names the sibling it is not (eth_balance for the native coin), so an agent can separate it from the other *_token_balance tools by chain name alone.

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?

"Use to check stablecoin or token holdings before a transfer or trade" gives the positive trigger, and "for the native coin use eth_balance" gives the explicit alternative. It further states when NOT to expect success (no contract → 404, non-ERC-20 → 422), which is decision-relevant routing information.

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