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

Goes well beyond the readOnly/idempotent/openWorld annotations by disclosing that this is a paid tool: x402 USDC on Base at $0.001 per successful call, and that calling without payment returns a PaymentRequired object. That payment flow is exactly the kind of behavioral detail an agent must know before invoking.

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-loads the call-to-action ("Use before sending a transaction") before the technical detail, and every clause carries information. The single dense sentence stacks many clauses, which slightly hurts scannability, but there is no filler.

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?

Covers purpose, trigger condition, data sources, output content (percentiles, base fee, gas price, L1 fee, action cost table in ETH and USD), and the payment mechanics. With no output schema, this is sufficient for an agent to call and interpret the tool 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% for the single optional chain parameter, so the baseline is 3. The description adds chain-conditioned behavior the schema does not capture — the L1 data fee upper bound applies only on Base — which meaningfully informs parameter choice.

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 the exact resource — gas and fee estimates — and enumerates the underlying reads: eth_feeHistory over 20 blocks, next base fee and gas price, L1 data fee via the OP-stack GasPriceOracle, and USD pricing of typical actions. This clearly separates it from siblings like dex_price, price, and tx.

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?

"Use before sending a transaction or to tell a user what it will cost" gives a concrete triggering condition. It does not name an alternative tool or a when-not case, but the usage context is unambiguous for so focused a tool.

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