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

Annotations give only hint flags, and the description goes well beyond them: the exact price ($0.0015 USDC), the no-charge-on-failure policy, the two-step x402 payment flow with the PaymentRequired retry and params._meta path, and that signing happens in the caller's wallet. That is substantial operational context an agent needs. It does not cover idempotency or whether repeated paid calls re-charge, leaving a small gap.

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 output inventory is front-loaded and every clause maps to a real capability. The main inefficiency is the price being stated twice, once inline ('$0.0015 USDC on Base') and again in the bracketed PAID block, plus the payment boilerplate lengthening an otherwise tight definition.

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?

Given an output schema exists, the description need not explain return values, yet it still summarizes them usefully. Combined with cost, failure semantics, and the full payment handshake, an agent has everything needed to invoke this paid 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 description coverage is 100%, so both `blocks` and `_x402_payment` are already documented in the schema. The description restates the 5–50 range and default without adding new meaning, which is the expected baseline when the schema does the work.

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 opens with a precise verb/resource statement ('Base gas price') and enumerates exactly what is returned: base fee, priority fee percentiles over the last 20 blocks, ready-to-sign maxFeePerGas values, L1 data-fee bound, and transfer cost estimates from Base mainnet. It is clearly distinguishable from siblings like ontario_base-balances and ontario_base-tx-check.

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 required/optional parameters and the caveat 'Estimates, not inclusion guarantees,' which implies usage for gas estimation. However, it never says when to prefer this tool over siblings or what conditions should steer an agent elsewhere; the guidance is implied rather than explicit.

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