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

Goes well past the annotations: latest-block semantics, dual-unit return, a 400 with no charge on malformed input, $0.01/call pricing with the first 25 free, and that failed calls are free while repeats are billed. The annotations only say read-only/non-destructive, so this cost and validation detail is real added value.

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 verb, resource, unit and block, then routing, then example, then pricing. Mostly every sentence earns its place, though 'Reads or computes only and changes nothing' restates readOnlyHint/destructiveHint and the pricing sentence is dense.

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 one-parameter read with no output schema, it covers scope, return units, failure behavior, cost, and alternatives. Nothing an agent needs to invoke 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% with '0x wallet or contract address' already documented, so the baseline is 3; the description adds a concrete example address and states the validation behavior (malformed address rejected with 400). It doesn't add anything beyond that, so it lands just above baseline.

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 the exact resource and method (native ETH balance via eth_getBalance on zkSync Era, latest block, returned in wei and ETH), and explicitly separates itself from zksync_token_balance and wallet_portfolio. An agent can pick this over its many siblings without opening a 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 a concrete use case (checking whether a wallet can pay gas or send a transfer) and names both alternatives with the condition that selects each: ERC-20 tokens go to zksync_token_balance, all holdings at once to wallet_portfolio.

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