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

Annotations already cover read-only, open-world, non-destructive, and non-idempotent hints. The description adds substantial context beyond them: live contract read, no state changes, charged repeats, $0.01/call pricing, first 25 free, failed calls free, and specific 404/422 error behavior.

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 description is front-loaded with purpose and routing, followed by operational details. It is dense but mostly justified because there is no output schema and pricing/error behavior matters; minor redundancy around charging and repeats slightly weakens concision.

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?

No output schema exists, so the description carries return-value responsibility and does so: raw amount, decimals, symbol, and human-readable amount. It also covers input format, failure modes, and charging, making it complete for this tool.

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 schema already explains that token may be a ticker or a 0x ERC-20 contract address. The description adds useful error details, but its claim that 'both inputs are 0x addresses' conflicts with the schema's ticker option and can mislead an agent about valid token inputs.

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 resource and operation: ERC-20 token balance of a wallet on Polygon PoS, with token symbol/contract detail and the balanceOf mechanism. It also explicitly differentiates from the native coin case by pointing to polygon_balance.

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 a clear use case: check stablecoin or token holdings before a transfer or trade. It also names the alternative for the native coin via polygon_balance, which is the key sibling distinction for this tool.

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