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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the description does not need to restate that. It adds useful context: the cost per call ($0.03 in USDC on Base via x402) and the inclusion of token decimals. However, it also misleadingly implies that the token parameter is optional ('if you pass a token'), while the schema marks it as required. This is a behavioral inaccuracy that undermines transparency.

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 description is two sentences long, front-loaded with the core purpose and use case, followed by a cost note. There is no redundant phrasing. The cost information is placed at the end, which is appropriate as a secondary detail. It is highly efficient and easy to scan.

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?

The description covers the core function and a use case, and the annotations cover safety. However, it lacks any mention of the return format (e.g., whether it returns a number, a string, or an object), which matters because there is no output schema. The misleading implication that token is optional also leaves the agent uncertain about required parameters. For a tool that must be called with two required parameters, this is a gap.

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 the baseline is 3. The description adds minimal parameter-level detail beyond the schema: it mentions that passing a token yields its ERC-20 balance with decimals, but it does not clarify the chain parameter or the requiredness of token. The cost note is unrelated to parameter semantics. Overall, it does not significantly enhance parameter understanding beyond what the schema already provides.

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?

The description clearly states the tool's function: it returns the native balance of an address and optionally the ERC-20 balance with decimals for a given token. The phrase 'verify a payment or a holding' reinforces the purpose. It is easily distinguished from sibling tools like precio, mercado, and velas, which focus on market data, not wallet balances.

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?

The description explicitly suggests a use case: 'Use it to verify a payment or a holding without opening a block explorer.' This implies when to use it, and the sibling list confirms no overlap with balance queries. However, it does not explicitly mention when not to use it or compare it to a specific alternative, so it stops short of a full routing guide.

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