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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so safety is covered; the description goes further by disclosing the billing model ($0.01/call via x402 USDC or card key, first 25 free, failed calls free) and explaining why repeats are not free — which reconciles the non-obvious idempotentHint=false. It also describes the returned fields, which matters since there is no output schema. It stops short of documenting rate limits or error behavior beyond 'failed calls free'.

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, returned fields, use cases, the sibling alternative and the cost model all appear in one front-loaded paragraph with little waste. It is dense and slightly crammed (pricing detail runs long relative to the core purpose), but no sentence is purely filler.

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?

For a single-optional-parameter read tool with no output schema, the description covers what is returned, when to use it, which sibling to prefer for the simpler case, and the pricing consequences of repeat calls. Nothing an agent needs in order to select and call this correctly is absent.

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 single 'blocks' parameter is fully documented in the schema with the same '5-100 (default 20)' range and default that the description repeats. The description adds only an illustrative 'blocks=20', so the baseline 3 applies — the schema does the real work here.

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 verb and resource — gas price history on Base via eth_feeHistory — and spells out exactly which fields come back (base fee in gwei, block fullness, 10th/50th/90th percentile priority fees, low/avg/high over the window). It also names the sibling it is not ('for the current price alone use base_gas'), so an agent can route between the two 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?

It states explicit use cases ('judge whether fees are rising, pick a priority fee or time a transaction') and an explicit exclusion with the alternative to use instead ('for the current price alone use base_gas'). The only missing piece is what to do on a non-Base chain, but the tool name scopes that already.

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