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

Annotations already cover safety (readOnlyHint=true, destructiveHint=false), and the description adds genuinely new operational facts: it 'reads or computes only and changes nothing', each call is charged, repeats are not free, failed calls are free, and payment works via x402 USDC or a card key at /credits with 25 free calls. This also explains the otherwise puzzling idempotentHint=false. Slight gap: no mention of latency, caching, or what happens if the node returns fewer than N blocks.

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-loaded with the resource and return contents before the routing hint and the commercial boilerplate. It is one dense paragraph, and the pricing/credits tail is longer than an agent needs, but every sentence carries information and none is a restatement of the title.

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 carries the full burden of describing the return payload, and it does so precisely (per-block base fee, fullness, three priority-fee percentiles, window summary). With a single optional parameter and complete usage/cost guidance, an agent has everything needed to call it and interpret the result.

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 documents 'How many recent blocks, 5-100 (default 20)', which the description largely repeats along with an example (blocks=20). The one added value is that the prose range is trustworthy where the raw minimum/maximum in the schema are sentinel numbers, but that is a thin increment over structured data.

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+resource ('Gas price history on Avalanche') and enumerates exactly what comes back: base fee in gwei per block, block fullness, 10th/50th/90th percentile priority fees, and low/average/high base fee over the window. It also names the sibling it is not ('for the current price alone use avax_gas'), so it is separable from avax_gas, arb_gas_history, base_gas_history and the dozens of other per-chain gas tools.

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 three concrete use cases ('judge whether fees are rising, pick a priority fee or time a transaction') and an explicit exclusion routing to avax_gas for a single current price. The when-not condition is stated, not inferred.

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