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

Annotations already cover the safety profile (readOnlyHint=true, destructiveHint=false); the description adds genuine value beyond that with pricing ($0.01/call via x402, first 25 free), the fact that failed calls are uncharged, and confirmation that nothing is mutated. It only stops short of explaining caching or why repeats are billed, which is a minor gap against otherwise strong disclosure.

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?

Purpose is front-loaded in the first clause and each subsequent sentence adds real information (use case, error codes, pricing). However, the dense semicolon-chained packing and the incorrect 'both inputs are 0x addresses' claim mean not every sentence earns its place cleanly.

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 steps in to name the returned fields, and it covers error paths, pricing, and mutation status—unusually complete for a balance read. The one shortfall is the inaccurate parameter-format statement, which undermines otherwise thorough coverage.

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%, but the description actively contradicts the schema: it states 'Both inputs are 0x addresses (40 hex characters)' while the input schema says the token parameter accepts a ticker such as USDC, USDT, WETH or DAI. This misinformation could steer the agent away from a valid call form, pulling the score below the baseline 3.

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+resource (ERC-20 token balance of a wallet on Sonic, via balanceOf) and explicitly distinguishes itself from the native-coin sibling sonic_balance. The return shape (raw amount, decimals, symbol, human-readable amount) is named up front.

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 an explicit use case ('check stablecoin or token holdings before a transfer or trade') and routes the agent to the correct alternative for the native coin ('use sonic_balance'). Error behavior (404 for no contract, 422 for non-ERC-20) further guides correct invocation.

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