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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered. The description adds genuinely new behavioral context that annotations cannot express: this is a paid call costing $0.001 USDC via x402. It stops short of explaining whether payment is automatic or how settlement works, so it is not a full 5.

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?

Two sentences, zero filler, and the primary capability is front-loaded ahead of the pricing note. Nothing could be removed without losing information.

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?

For a single-parameter read tool with safety annotations, the description covers what it does, the chain, and the cost. It omits the return-value format (wei vs decimal ETH) and the actual payment mechanics, and with no output schema and no parameter description, those gaps are left entirely to the caller.

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 description coverage is 0%, so the description carries the burden; "any Base address" does clarify that the input is a Base-network address rather than an arbitrary string. However, it adds no format, casing, or checksum detail beyond the regex already in the schema, leaving the one required parameter thinly documented.

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?

"Native ETH balance of any Base address" states a specific verb (return balance) and resource (native ETH) plus the chain scope. The word "Native" implicitly distinguishes it from the ERC20 sibling `base_erc20_balance`, so an agent can route without opening the 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?

No when-to-use guidance, no prerequisites, and no alternative named. The description never tells the agent when to prefer this over `base_erc20_balance`, `base_portfolio`, or `base_call`; the agent must infer it from the word "Native".

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