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

Annotations already cover readOnly/destructive/openWorld, and the description adds genuinely new behavioral context: per-call pricing ($0.01 via x402 USDC or card key), a 25-call free tier, failed calls free, and that repeats are charged (consistent with idempotentHint=false). It does not cover error modes or latency, but the cost model is material and non-obvious.

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?

A single dense paragraph that front-loads what is returned, then usage, then cost. Every sentence carries information, though the pricing/credits clause at the end is slightly tacked on and could be separated for readability.

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 must explain return values, and it does so thoroughly (per-block base fee and fullness, three priority-fee percentiles, window aggregates). For a one-optional-parameter read tool, an agent has everything needed to call it 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?

Schema description coverage is 100%, and the schema already states "How many recent blocks, 5-100 (default 20)". The description restates the same range and default plus an example (blocks=20), adding only marginal meaning beyond the schema, so baseline 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 Linea via eth_feeHistory) and enumerates exactly what is returned: base fee per block, block fullness, 10th/50th/90th percentile priority fees, and low/average/high base fee. It explicitly contrasts with the sibling linea_gas for the current price alone, so the agent can pick between them without opening either 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 guidance ("judge whether fees are rising, pick a priority fee or time a transaction") and names the alternative plus the condition that selects it ("for the current price alone use linea_gas"). Nothing about tool selection 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.