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

Annotations already declare readOnlyHint=true and destructiveHint=false, but the description adds real context: latest block only, dual unit output, 400 rejection of malformed addresses with no charge, and per-call pricing with 25 free calls. The note that repeats are not free usefully explains the idempotentHint=false flag rather than contradicting it. It stops short of describing the exact response envelope, which is the only minor gap.

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 the core operation and units, then routing guidance, then validation and pricing. The pricing/billing sentence is the longest and only marginally relevant to invocation, but every other clause carries information an agent needs.

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 no output schema, the description covers return units (wei and ETH), block scope (latest), error behavior, and costs. Nothing needed to call it 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 100%, so baseline is 3, but the description adds that the address may be a wallet or contract, that any 0x address works, and supplies a concrete example value. It also specifies the failure behavior for malformed input, which the schema does not convey.

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 and resource: native ETH balance (eth_getBalance) of any 0x address on Base at the latest block, reported in wei and ETH. It explicitly separates itself from base_token_balance (ERC-20) and wallet_portfolio (all holdings), so an agent can pick it 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?

Gives an explicit use case (check whether a wallet can pay gas or make a transfer) and names both alternatives with the condition that selects each. No inference is needed to route between this and its siblings.

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