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

Annotations already cover read-only, non-destructive, non-idempotent, open-world, but the description adds genuinely new behavior: reverting transactions return 422 with the reason and are uncharged, and each successful call is billed so repeats are not free. The pricing/payment path (x402 USDC, card key, first 25 free) further clarifies cost consequences. Only the precise response shape for success is left implicit, which is minor for a no-output-schema tool.

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 the verb and resource, then inputs, then alternatives, then behavior and pricing — a sensible ordering with no filler sentences. It is slightly long, and the payment/billing block is dense, but every clause carries actionable 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?

For a four-parameter, read-only estimator with no output schema, the description covers what is returned (gas units, gwei, ETH), the failure mode (422 with revert reason, uncharged), the cost model, and which sibling to use instead. Nothing an agent needs in order 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%, so the baseline is 3, but the description adds real nuance: value is expressed in ETH and the sender is required only when the call depends on it. The inclusion of a concrete example address (to=0x...dEaD) also anchors the expected address format beyond the schema's generic '0x recipient or 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 — estimate gas for a transaction on Arbitrum One — and names the underlying method (eth_estimateGas) plus exactly what is returned (gas units, gwei, ETH cost). It explicitly distinguishes itself from the sibling arb_gas, which only reports gas price, so an agent can route correctly without opening either 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 concrete when-to-use triggers ('before sending a transaction or to price a batch') and an explicit when-not/alternative ('for the gas price alone use arb_gas'). It also states the preconditions for inputs ('sender when the call depends on it'), leaving nothing to inference.

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