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

Annotations already cover safety (readOnlyHint=true, destructiveHint=false), so the description's real contribution is the cost model ($0.01/call via x402 or card key, first 25 free, failed calls free) and the explicit non-idempotency explanation ("each call is charged, so repeats are not free"), which reconciles idempotentHint=false with a pure read. It also documents the 422-on-non-contract behavior. Missing: any statement about latency or rate limiting, though these are minor for a single-call read.

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 use cases, then input format, then error behavior, then pricing — a sensible ordering with no filler. Slight redundancy at the tail, where "each call is charged, so repeats are not free" restates the pricing sentence immediately before it.

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 all four returned fields. Combined with input format, error semantics, cost, and the sibling alternative for balances, an agent has everything needed to call this correctly on the first attempt.

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 says the input is a ticker or 0x address, so baseline is 3. The description goes further by giving a concrete example address and explaining that a non-ERC-20 address is rejected rather than returning empty data, which is meaning the schema does not carry.

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?

Specific verb and resource ("Look up the name, symbol, decimals and total supply of an ERC-20 token contract on Scroll") with the returned fields enumerated. It explicitly separates itself from the nearest sibling ("for a holder's balance use scroll_token_balance"), so an agent can route correctly from the description alone.

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?

Names two concrete use cases (identifying an unknown token address, formatting raw amounts) and a named alternative with the condition that selects it. Also states a failure boundary (non-ERC-20 address returns 422, uncharged), which removes ambiguity about what happens on a bad input.

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