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

Annotations already cover read-only and non-destructive behavior, but the description adds genuinely new context: the per-call charge ($0.01 via x402 USDC or card key), the 25 free calls, that failed calls are free, and that repeats are not free — which explains the idempotentHint=false in practical terms. It stops short of describing error modes or latency, so it is not quite maximal.

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?

Purpose and return contents are front-loaded, and each sentence carries information. The billing sentence is long and slightly crowds out the technical content, but it is not redundant padding given the cost is a real decision factor for repeated calls.

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, and the description compensates by enumerating the returned metrics in detail, plus scope limits, cost, and the alternative tool. For a single optional-parameter read tool, nothing an agent needs to call it correctly 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 schema already states 'How many recent blocks, 5-100 (default 20)'. The description repeats that range and adds only an example (blocks=20), so it contributes no meaning beyond the structured field — 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?

The description names the exact underlying call (eth_feeHistory) and enumerates the returned fields: base fee in gwei, block fullness, 10th/50th/90th percentile priority fees, and low/average/high base fee over the window. It also explicitly opposes itself to the sibling sei_gas ('for the current price alone use sei_gas'), so an agent can pick between them 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?

It gives concrete decision contexts ('judge whether fees are rising, pick a priority fee or time a transaction') and an explicit exclusion routing to the alternative tool for the current price only. This is exactly the when-to-use/when-not pattern at the top of the scale.

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