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

Goes well beyond the annotations by disclosing the error behavior (422, uncharged), the fact that failed calls are free, the pricing model ($0.003/call via x402 USDC or card key, first 25 free), and explicitly explains the counterintuitive readOnlyHint=false ('not marked read-only because each call is charged'). This resolves what would otherwise look like an annotation mismatch.

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 purpose, then usage, then mechanics, then pricing; the ordering is sensible and no sentence is redundant. It is dense and slightly long, with the pricing/credit sentence being the least essential part, but it still earns its place by answering cost questions.

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, yet the description enumerates the returned fields (name, symbol, decimals, total supply), covers the single input, the failure mode, and the billing model. An agent has everything needed to call this 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 the baseline is 3, but the description adds the constraint type ('the token's 0x contract address') and a concrete valid example value, which is more than the schema's terse '0x ERC-20 token contract address'.

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 ('look up the name, symbol, decimals and total supply of an ERC-20 token contract on Polygon PoS') and explicitly names the sibling it is not for ('for a holder's balance use polygon_token_balance'). An agent can distinguish it from the rest of the polygon_* family without opening any 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 two concrete use cases ('identify an unknown token address', 'format raw amounts') and an explicit exclusion routing balance queries to polygon_token_balance. Also states the failure precondition: a non-ERC-20 address returns 422, uncharged.

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