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

Annotations already mark it read-only and non-destructive, but the description adds disclosure the annotations cannot: pay-per-call billing, 25 free calls, failed calls free, and explicitly that repeated identical calls are still charged — which explains and reinforces the idempotentHint=false annotation. That billing/repeat-cost warning is exactly the kind of behavioral context an agent needs before looping.

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 what is returned, then usage, then an example, then pricing. Every sentence carries information, though the trailing pricing/licensing clause is slightly long relative to the single-parameter payload.

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 must carry the return shape — and it does, specifying per-block base fee, fullness, three priority-fee percentiles, and window-level low/average/high. Combined with usage and billing notes, an agent has everything needed to call and interpret 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% and the schema already documents 'How many recent blocks, 5-100 (default 20)'. The description restates the same range and default and adds only the trivial example blocks=20, so it adds little beyond the structured field.

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: gas price history on Optimism via eth_feeHistory, and enumerates exactly what is returned (base fee in gwei per block, block fullness, 10/50/90th percentile priority fees, low/avg/high base fee). It explicitly separates itself from op_gas by scoping that sibling to 'current price alone'.

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 or time a transaction') and names the alternative tool with the condition that selects it ('for the current price alone use op_gas'). An agent does not need to infer when to pick this over op_gas.

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