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

Annotations cover the safety profile (readOnly, idempotent, non-destructive), and the description adds substantial context they don't carry: the $0.075 per-call price, that bad input is rejected before any charge, that the default return is an unpaid x402 request body rather than data, and that a P0 key causes the call to be paid and the balance deducted. The only gap is pagination/result-shape detail, minor given the tool returns a request payload or data directly.

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 case and the sibling alternative are front-loaded, followed by payment mechanics, which is a sensible ordering. It is dense but nearly every sentence carries operative information; the long key-purchase URL is the one element that could be compressed.

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?

With no output schema, the description correctly explains what actually comes back — a paid x402 request body plus a schema link, or the data itself when a P0 key is used. Combined with the pricing and pre-charge validation notes, an agent has everything needed to invoke it correctly.

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 both parameters are already documented, and the description largely restates them (25-address cap, chain list). It does add one piece of meaning beyond the schema by naming '0x or ENS names' as accepted address formats, but otherwise leaves the heavy lifting to the schema — baseline 3.

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?

The description opens with a specific verb and resource: native and stablecoin balances for a list of wallets, capped at 25 addresses in one POST. It explicitly names the sibling wallet_balance as the single-address alternative, so an agent can distinguish the two without inspecting schemas.

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?

It states the triggering condition (need balances for a list of wallets) and gives an explicit routing rule: 'For one wallet use wallet_balance.' It also explains the two operating modes — raw x402 request construction vs. auto-paying with a P0 key — which determines how the agent should proceed.

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