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

Beyond the annotations, it discloses the error contract (404 for no contract, 422 for non-ERC-20, both uncharged), the billing model ($0.01/call via x402 or card key, first 25 free, failures free), and the non-idempotent cost note that repeats are not free. This adds substantial operational context the readOnly/openWorld hints alone do not convey.

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 core purpose and the sibling routing are front-loaded in the first two clauses, and no sentence is pure filler. It is dense and slightly long, with pricing and error details stacking up, but each clause carries usable 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?

With no output schema, the description compensates by enumerating the returned fields (raw amount, decimals, symbol, human-readable amount). Combined with error codes, input constraints, cost, and safety profile, an agent has everything needed to call it correctly and interpret the result.

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 real constraints the schema lacks: both inputs must be 0x addresses of 40 hex characters, and the token argument accepts either a ticker or a contract address. That format guidance meaningfully improves invocation accuracy, though it stops short of documenting all edge cases.

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?

The description names a specific verb and resource ('ERC-20 token balance of a wallet on Scroll'), specifies the mechanism (balanceOf), and enumerates both the exact return fields and the accepted token forms. It explicitly distinguishes itself from the native-coin sibling scroll_balance, so an agent can route correctly without opening another 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?

It states the concrete use case ('check stablecoin or token holdings before a transfer or trade') and names the alternative with the condition that selects it ('for the native coin use scroll_balance'). When-to-use and when-to-use-something-else are both explicit.

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