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

With no annotations, the description does real work: it discloses the 10s cache TTL, the paid x402 cost of $0.001, and that data comes from eth_feeHistory. The one weak point is the 'optional eth-transfer USD estimate' — nothing in the schema lets the caller request it, so the behavior is stated but not actionable, and no error/rate-limit behavior is described.

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?

Four short sentences, front-loaded with what is returned and for which chains, then cache, optional feature, and price. Every sentence carries distinct operational information with 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?

For a 2-parameter, no-output-schema tool this is largely sufficient: it names the metrics, the chains, the data source, price, and caching. The gaps are the un-parameterized USD estimate and the absence of any note on output shape when both chains are requested.

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 50%; request_id is fully documented in the schema itself, and the description adds meaning only for 'chains' by saying 'Base and/or Ethereum'. It does not explain default behavior when chains is omitted, nor the per-chain output differences, so it neither compensates for the coverage gap nor adds much beyond it.

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?

Names a concrete resource (EIP-1559 base fee and priority fee percentiles p25/p50/p90) over specific chains, and discloses the underlying source (eth_feeHistory). It is clearly distinguishable from siblings like token_price or llm_cost_quote, so an agent knows exactly what this returns.

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?

Usage is only implied by the subject matter — call it when you need gas fees. There is no explicit when-to-use/when-not, no routing to alternatives (e.g. erc20_meta or token_price for token-level pricing), and no stated defaults beyond the schema's 'base' default.

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