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

With no annotations, the description carries the full burden and does add real operational context: exact cost ($0.005 per call), the payment rail (x402/USDC), the data source and window (eth_feeHistory, last 20 blocks), and the percentiles returned. It does not cover failure modes (e.g. unsupported chain, payment failure), which keeps it short of a 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 what is returned and followed by why it matters and the operational facts. The '$0.005 per call, paid over x402' line is dense but earns its place as cost transparency; nothing is 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?

There is no output schema, so the description must describe returns, and it does so concretely (two fee fields, three speed percentiles). Cost, source, and payment method are covered; the only meaningful gap is sibling differentiation against evm_gas/evm_estimate_gas.

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% and the single chain parameter has its allowed values documented inline in the schema, so the schema carries the semantics. The description says nothing about chain, but with full schema coverage that is an acceptable baseline.

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?

It states a specific resource and outputs (maxFeePerGas and maxPriorityFeePerGas from the last 20 blocks, at slow/normal/fast percentiles) and names the upstream RPC method (eth_feeHistory). It is clear what the tool returns, but it never distinguishes itself from siblings evm_gas or evm_estimate_gas, leaving ambiguity about which fee tool to pick.

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?

'Beats guessing a gas price and getting stuck in the mempool' gives an implied motivation for using it, and the stated price signals a paid premium path. But there is no explicit when-to-use/when-not and no reference to evm_gas or evm_estimate_gas, which are the obvious alternatives an agent must weigh.

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