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

Discloses pricing ($0.003/call, x402 or card key, first 25 free), failure semantics (malformed address -> 400 uncharged, failed calls free), and return format (wei and POL). Crucially it explains the seemingly odd readOnlyHint=false annotation ('not marked read-only because each call is charged'), converting a potential contradiction into clear behavioral context.

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-loads purpose, then usage/alternatives, then example, then pricing/auth, then the readOnly rationale. Dense but every sentence carries distinct, non-redundant information.

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 single-param read tool with no output schema, it covers everything an agent needs: what is returned (wei and POL), cost/auth model, error behavior, and correct routing against siblings.

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 earns an extra point by reinforcing the expected 0x format with a concrete example address and by documenting the validation outcome (400, uncharged) that the schema cannot express.

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 (Read), resource (native POL balance), and scope (any 0x address on Polygon PoS at the latest block, in wei and POL). It explicitly names the siblings it is not (polygon_token_balance, wallet_portfolio), so an agent can route 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 explicit when-to-use ('check whether a wallet can pay gas or a transfer') and two named alternatives with the selecting condition (ERC-20 -> polygon_token_balance, all holdings -> wallet_portfolio). Nothing is left to inference.

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