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

The annotations already declare readOnlyHint=true, destructiveHint=false, and idempotentHint=false, and the description reinforces this with 'reads or computes only and changes nothing'. The pricing details (first 25 requests free, $0.01 per call via x402 USDC or card key) add useful context for the non-idempotent, charged nature of the tool, but the return formatting and data-window freshness are not elaborated beyond the field list.

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-loads the returned data, then usage and alternative, then an example, then pricing — each sentence is purposeful with no filler. The density is high but every clause adds value.

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?

With no output schema, the description fully enumerates the returned fields and their units, so callers know what to expect. For a one-parameter read-only tool, nothing essential is missing.

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 schema already documents the 5-100 range and default of 20 for the single parameter. The description repeats this information and adds only an example value, which does not meaningfully extend the schema.

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 the specific verb and resource (gas price history on HyperEVM via eth_feeHistory) and enumerates the returned fields: base fee in gwei per block, block fullness, 10th/50th/90th percentile priority fees, and low/average/high base fee. It explicitly distinguishes itself from the sibling hyperevm_gas, which returns only the current price.

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 concrete decision contexts — judge whether fees are rising, pick a priority fee, time a transaction — and names the alternative with the condition that selects it: 'for the current price alone use hyperevm_gas'. It also supplies a usage example (blocks=20).

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