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

Annotations already cover the safety profile (readOnlyHint true, destructiveHint false), and the description adds cost behavior that no annotation carries: $0.01/call via x402 USDC or card key, first 25 free, failed calls free, and that repeat reads are not free. The 'reads or computes only and changes nothing' line is consistent with readOnlyHint, though it sits slightly at odds with idempotentHint=false — the charge-per-call explanation resolves that rather than contradicting it.

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?

The first sentence front-loads the purpose and the return shape, followed by usage guidance, an example, and pricing. It is dense and every clause carries information, though the pricing/credits tail is long enough to slightly dilute the core message.

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?

There is no output schema, so the description takes responsibility for describing return contents (per-block base fee, fullness, percentile priority fees, window aggregates) and does so fully. Combined with the parameter range, cost model, and usage routing, an agent has everything needed to call it correctly and interpret results.

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?

With 100% schema description coverage, the schema already documents the single 'blocks' parameter with range 5-100 and default 20. The description restates the same range and default plus an example (blocks=20) but adds no interpretation of the parameter beyond the schema, so the baseline of 3 applies.

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 and resource ('Gas price history on Base (eth_feeHistory)') and enumerates the returned quantities: base fee in gwei per block, block fullness, 10th/50th/90th percentile priority fees, and low/avg/high base fee. It also names the sibling it is not ('for the current price alone use base_gas'), so differentiation is unambiguous.

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 selection criteria ('judge whether fees are rising, pick a priority fee or time a transaction') and an explicit exclusion routing to base_gas when only the current price is needed. Nothing about when to choose this over its alternatives 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.