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

Annotations already cover the read-only, non-destructive, open-world profile, and the description adds cost behavior the annotations cannot express: $0.01/call via x402 USDC or card key, first 25 free, failed calls free, and that repeats are not free because each call is charged. It also reaffirms 'reads or computes only and changes nothing', which aligns with readOnlyHint and explains the non-idempotent cost model.

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 return contents, then usage, then pricing. Dense and mostly waste-free, though the range/default is repeated verbatim from the schema and the payment details run slightly long.

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, but the description enumerates the returned shape (per-block base fee, fullness, priority fee percentiles, plus window-level low/avg/high), which is exactly what an agent needs to interpret results. For a one-parameter read tool, nothing material 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 single blocks parameter is already documented as 5-100 with default 20 in the schema. The description restates that range and default and adds an example (blocks=20), which is mildly reinforcing but not new semantics. Baseline 3 applies when the schema does the heavy lifting.

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 specific verb and resource (gas price history on Optimism via eth_feeHistory) and enumerates the exact contents: base fee in gwei, block fullness, 10th/50th/90th percentile priority fees, and low/avg/high base fee. It explicitly distinguishes itself from sibling op_gas for the current price, so an agent can route without opening a schema.

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 when-to-use cases (judge whether fees are rising, pick a priority fee, time a transaction) and names the alternative (op_gas) with the condition that selects it (current price alone). Nothing is left to inference.

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