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

Annotations already cover readOnly/idempotent/openWorld/non-destructive, yet the description adds material behavior beyond them: the call is a paid x402 request at $0.075, it returns a request body to POST rather than the data itself, and bad input is refused before any charge. These are exactly the traits an agent cannot learn from annotations or schema.

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 use condition and scope are front-loaded, and the closing sibling reference is well placed. The middle sentence about the x402 request, pricing, and response schema is dense but each clause carries distinct information, so little is wasted.

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 two-parameter tool with no output schema, the description covers what is returned (the paid request plus response schema and example), the invocation path, the price, and the failure policy. Nothing an agent needs in order 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 the baseline is 3. The description adds the accepted address formats (0x or ENS names) and the 25-address cap, which slightly enriches the addresses parameter, but it says nothing about the optional 'chains' parameter beyond what the schema already documents.

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 and stablecoin balances for a list of wallets) plus the scope (up to 25 addresses in one POST). It explicitly distinguishes itself from the sibling wallet_balance by naming it as the single-wallet alternative.

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?

Opens with the use condition ('when you need native and stablecoin balances for a list of wallets') and closes with the routing rule 'For one wallet use wallet_balance.' The batch-vs-single decision is fully specified with no inference required.

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