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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered. The description adds real context beyond them: the upstream data source (eth_feeHistory), the network (Base Mainnet), and the cost model (0.0020 USDC per call, first call free), which matters for an agent deciding whether to spend a call. It stops short of rate limits or failure behavior, so a 4 rather than 5.

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?

Three tight sentences, front-loaded with the scope constraint ('Gas ONLY') before the routing advice and price. Every clause carries distinct information: data source, outputs, alternative, cost.

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, but the description compensates by naming every returned field (base fee latest/average, percentile bands, congestion label) along with the price. An agent has enough to decide and invoke without further documentation.

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?

The tool takes zero parameters, which is the baseline-4 case. The description correctly implies no configuration is needed and spends its words on outputs instead of inventing parameter guidance.

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 ('live Base Mainnet gas from eth_feeHistory') and enumerates the exact outputs: latest and 10-block average base fee in gwei, p25/p50/p75 priority-fee percentiles, and a congestion label. It explicitly marks itself as gas-only, which separates it cleanly from market-snapshot and the pricing siblings.

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 an explicit when-to-use ('when you need gas and nothing else') and names the alternative with the condition that selects it ('if you also want WETH/USDC pricing, use market-snapshot instead'), even quantifying the tradeoff as one cheaper call. No inference required.

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