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

Annotations already declare readOnlyHint=true, destructiveHint=false, openWorldHint=true, but the description adds substantive context beyond them: the pricing model ($0.01/call via x402 USDC or card key, first 25 free, failed calls free) and the clarification that each call is charged so repeats are not free — which explains the otherwise puzzling idempotentHint=false. It could have gone further on latency or response size, but the cost and repeat-charging disclosure is genuinely useful.

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?

It is front-loaded with what the tool returns, then usage, then cost — a sensible order with no filler sentences. It is dense and slightly long, and the blocks example is largely redundant with the stated default, which keeps it from a 5.

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, but the description compensates by enumerating the returned metrics (per-block base fee, fill ratio, percentile priority fees, window low/average/high), so an agent knows what comes back. Combined with cost, safety, and the arb_gas alternative, it is nearly complete; only things like pagination or per-block metadata limits are unaddressed.

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 single parameter already documents 'How many recent blocks, 5-100 (default 20)'; the description restates that range and default verbatim rather than adding new meaning. The 'Example: blocks=20' adds little since 20 is already the default. Baseline 3 applies when the schema carries the parameter documentation.

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 a specific chain (Arbitrum One), a specific RPC method (eth_feeHistory), and enumerates exactly what is returned: base fee in gwei per block, block fullness, 10th/50th/90th percentile priority fees, and low/average/high base fee over the window. It explicitly distinguishes itself from the sibling arb_gas, noting that tool is for the current price alone.

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 three concrete use cases (judge whether fees are rising, pick a priority fee, time a transaction) and names the alternative for the current-price case: 'for the current price alone use arb_gas'. This is an explicit when-to-use plus when-to-use-something-else routing statement.

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