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

Goes well beyond the readOnly/openWorld/idempotent annotations by disclosing the cost ($0.075 per call), the charge-protection rule ('bad input is refused before any charge'), the required auth header (Authorization: Bearer p0k_…), where to buy a key, and that the default return value is a request spec rather than data. For a paid, open-world tool this is exactly the missing context annotations cannot carry.

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 trigger and scope, then pricing, then the two modes — a sensible order. Slightly over-packed (price restated as both '$0.075 per call' and 'deducting the listed price', plus a long key-purchase URL inline) which costs a bit of scanability.

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 tells the agent what comes back in each mode (an x402 POST body with response schema and example, or the actual data with a key) and covers payment, auth, and input limits. It never sketches the shape of the balance payload beyond 'native and stablecoin balances', which is a minor gap for a tool with no output schema.

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 addresses (1-25, duplicates removed) and chains are already documented; the description only adds that entries may be 0x addresses or ENS names, which the schema omits. The 'chains' parameter is not mentioned in the description at all, so value added over the schema is marginal and the baseline 3 applies.

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 hard scope ('up to 25 addresses ... in one POST'). It also explicitly contrasts with sibling wallet_balance ('For one wallet use wallet_balance'), so the agent can pick between them 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?

Opens with an explicit 'Use when you need...' trigger, names the alternative (wallet_balance) for the single-wallet case, and explains the two invocation modes: default returns an x402 request to POST yourself, or with a P0 access key the tool performs the paid call. Nothing about when-to-use is left implicit.

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