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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and non-destructive. The description adds the cost of $0.001 USDC per call and notes byte-identical equivalence to a specific REST endpoint, which are behavioral traits beyond the annotations. It does not cover rate limits or pagination, but for a read-only tool this is adequate.

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 description is moderately long but every sentence adds value: functionality, limitation, cost, supported chains, and REST equivalence. It is front-loaded with the primary purpose, and the structure is logical. It could be trimmed slightly but remains efficient and informative.

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 the existence of an output schema and annotations covering safety, the description provides sufficient context: purpose, when to use vs. alternative, cost, chain support, and a concrete REST equivalent. No critical information is missing for an agent to correctly invoke this tool.

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 both chain and blocks parameters, each with clear descriptions. The description does not add any parameter-specific details beyond what the schema already provides, such as syntax or format. With full schema coverage, the baseline of 3 is appropriate.

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 clearly states it retrieves eth_feeHistory over a bounded window, detailing the exact data (base fee plus 25/50/75 priority-fee percentiles). It also differentiates from the sibling chain_fee_data by explicitly stating that a single instantaneous quote cannot answer whether gas is rising, making its purpose unambiguous and distinct.

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 explicitly contrasts with /chain/fee-data (instantaneous quote) and explains that this tool is needed to assess fee trends over multiple blocks. It also lists supported chains and a REST equivalent, but it does not name other potential alternatives like chain_gas_estimate or gas_prices, so the guidance is clear but not exhaustive.

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