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

Annotations already cover readOnly/destructive, but the description goes well beyond them: it discloses pricing ($0.01/call, first 25 free, failed calls free), that a malformed address returns 400 uncharged, and that repeated calls are re-charged — which explains the non-obvious idempotentHint=false. That billing and error behavior is exactly the context annotations cannot express.

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 resource and chain, then siblings, then error/billing notes, then the read-only reassurance. Dense but every sentence carries information; the billing tail is slightly repetitive ('each call is charged, so repeats are not free' after already stating price per call).

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 tool with no output schema, the description supplies the return shape (wei and AVAX, latest block), the error path, the cost model, and the sibling routing. Nothing an agent needs to call it correctly or interpret the result 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% and the single parameter is self-explanatory, so the baseline is 3. The description adds real meaning on top: a concrete example address and the behavior for a malformed value (rejected with 400, uncharged), which tells the agent what valid input looks like and what a bad input costs.

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 AVAX balance of a 0x address on Avalanche at the latest block, returned in wei and AVAX. It also names the underlying call (eth_getBalance) and explicitly distinguishes itself from avax_token_balance (ERC-20) and wallet_portfolio (all holdings), so an agent can route without opening another 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 (checking whether a wallet can pay gas or a transfer) and names both alternatives with the condition that selects each: ERC-20 tokens go to avax_token_balance, all holdings go to wallet_portfolio. When-not guidance is implicit but unambiguous.

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