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

Adds real behavioral context beyond annotations: values are read live from the contract (not cached) and each successful call costs $0.001 USDC on Base via x402. This pricing/auth detail is exactly the kind of thing annotations cannot express and materially affects invocation. Note the mild tension between 'read live from the token contract' and readOnlyHint=false/idempotentHint=false, which the per-call payment plausibly explains rather than contradicts.

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?

Three dense, front-loaded sentences: identity first, then usage, then cost. No filler, no repetition of the name or title.

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?

There is no output schema, and the description compensates by naming the return shape (raw amount, decimals, symbol, human-readable amount), plus the chain and the payment model. For a 2-parameter read with full schema coverage, nothing an agent needs 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 description coverage is 100%, with both params ('token', 'address') documented as 0x addresses. The description adds no syntax, format, or validation detail beyond the schema, so the baseline of 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+resource+chain: 'ERC-20 token balance of a wallet on Polygon PoS', and enumerates the returned fields. An agent can immediately distinguish it from polygon_balance (native) and polygon_token_info (metadata) 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 a clear use case: 'check stablecoin or token holdings before a transfer, payment or trade.' It does not name alternatives or state when-not to use it (e.g., versus polygon_token_info or polygon_balance), so it falls short of an explicit routing rule.

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