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

Annotations already declare read-only and non-destructive, but the description adds behavior the annotations cannot express: it is compute-only and changes nothing, every call is billed ($0.01 via x402 USDC or card key), the first 25 calls are free, failed calls are free, and repeats are not free — which explains the otherwise puzzling idempotentHint=false. This is substantive context beyond structured fields.

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-loads the operation and return contents, then usage, example, and pricing — a sensible order. It is a dense run-on paragraph and the pricing sentence is long, but nearly every clause carries information an agent needs (cost, free tier, no-op behavior).

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 describe returns, and it does: per-block base fee in gwei, block fullness, three percentile priority fees, and low/avg/high over the window. Combined with the usage and billing context, 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 repeats the same range and default, and the example 'blocks=20' adds no new meaning. Baseline 3 applies since the schema carries the parameter 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?

Names a specific verb+resource+chain: gas price history on Unichain via eth_feeHistory, and enumerates what the result contains (base fee per block in gwei, block fullness, 10/50/90th percentile priority fees, low/avg/high over the window). It also explicitly distinguishes itself from the sibling unichain_gas ('for the current price alone'), so an agent can route 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 cases ('judge whether fees are rising, pick a priority fee or time a transaction') and an explicit alternative for the other case ('for the current price alone use unichain_gas'). No inference is required to choose between the two.

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