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

Annotations already declare readOnlyHint=true, idempotentHint=true and destructiveHint=false, so safety is covered. The description adds genuine extra context beyond the annotations: the data source ('our own Reth node') and the scope of what is computed (percentiles over the last blocks, cost of a plain vs ERC-20 transfer). It does not mention freshness/caching or rate limits, which keeps it from 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?

Front-loaded with the resource and data source, followed by compact when/when-not clauses and a return listing. The trailing Returns field list is dense but justified because no output schema exists; nothing is truly wasted.

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?

No output schema exists, so the description carries the burden of describing return values, and it does so with concrete field names. Combined with the usage routing and data provenance, an agent has everything needed to call and interpret the 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?

The tool takes zero parameters, so the baseline is 4. There are no argument semantics to add, and the description correctly focuses on outputs rather than 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+resource (Ethereum fee market) and enumerates the exact data returned: base fee, next base fee, priority percentiles, and transfer cost estimates. It explicitly names the sibling tools it is NOT for (btc_get_fee_rates, xmr_get_fee_rates, tron_get_chain_economics), so an agent can select it without ambiguity.

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?

Explicit when-to-use ('pricing an Ethereum transaction, or deciding what tip gets included quickly') plus an explicit do-not-use clause routing to the correct chain-specific alternatives. Both the positive and negative conditions are named.

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