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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds valuable behavioral context beyond annotations: the exact fee components returned, the 21000-gwei transfer assumption, the per-call cost, and the byte-identical equivalence to a specific REST endpoint. It also discloses the chain list. The only minor gap is not describing the output schema structure, but an output schema exists, so that burden is reduced.

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?

Three sentences, each earning its place: the first defines the output and scope, the second gives the cost, the third lists chains and the REST equivalence. The most decision-relevant information (what it returns, cost, chains) is front-loaded. No filler or repetition of schema content.

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-parameter read-only tool with a full output schema, the description is complete. It tells the agent what the tool returns, which chains are valid, what the call costs, and that it matches a known REST endpoint. The annotations cover safety, and the output schema covers return structure. Nothing an agent needs to decide whether to call this tool 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 single parameter 'chain' is already described in the schema with the allowed values. The description adds value by listing the supported chains again in prose and by clarifying that the quote is for 'one chain' at a time. With only one parameter and full schema coverage, the description doesn't need to do much more; the baseline 3 is exceeded slightly because the description reinforces the chain-key semantics and the per-chain scope.

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 states a specific verb ('get' implied via 'what sending costs right now'), a clear resource (EIP-1559 fee quote), and enumerates the exact fields returned (gasPrice, base fee, priority fee, all-in cost of a 21000-gwei transfer in wei and native units). It also names the supported chains, which distinguishes it from generic fee tools. The title 'Full EIP-1559 fee quote' reinforces the resource. This is clearly differentiated from siblings like chain_fee_history and gas_prices.

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?

The description implies when to use it: when you need current EIP-1559 fee components and the all-in cost of a standard transfer on a specific chain. It names the supported chains and notes the cost per call ($0.001 USDC), which is a practical usage consideration. However, it doesn't explicitly state when NOT to use it or name alternatives like chain_fee_history or gas_prices, so it misses the explicit exclusion/alternative guidance that would earn a 5.

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