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

Adds real context beyond the annotations: it names the underlying RPC method (eth_feeHistory), discloses billing ($0.01/call, first 25 free, failed calls free), and explains why repeats are not free, which directly motivates idempotentHint=false. Missing only deeper operational detail such as rate limits or latency.

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 pricing; every clause is relevant, including the billing note since calls are charged. The final billing sentence is slightly long relative to the rest, keeping it just short of a 5.

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 return-value burden and does so: it enumerates base fee per block, block fullness, 10th/50th/90th percentile priority fees, and window-level low/average/high. Combined with the usage and pricing context, an agent has everything needed to call it correctly.

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 parameter already carries the 5-100 range and default 20, so the description's restatement is redundant. The 'Example: blocks=20' adds a small amount of practical guidance but no new constraint semantics.

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 (returns historical gas prices) and resource (Polygon PoS fees via eth_feeHistory), and explicitly contrasts with sibling polygon_gas for the current price alone. Its output content (base fee per block, block fullness, priority fee percentiles, window low/average/high) is concrete enough to distinguish it from every other gas tool in the family.

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 explicit use cases ('judge whether fees are rising, pick a priority fee or time a transaction') and an explicit exclusion with the alternative named ('for the current price alone use polygon_gas'). Nothing is left to inference about when to pick this over the sibling.

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