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

Annotations already cover the read-only/idempotent/non-destructive profile, and the description goes further by disclosing the exact payload contents and — importantly — that each call costs $0.003 USDC via x402 on eip155:8453. That cost disclosure is genuine behavioral context an agent needs before invoking. It stops short of stating data freshness, caching, or what happens with unsupported chains.

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?

Two sentences, front-loaded with purpose and then return contents and price. Every clause carries information, though the opening clause duplicates the title verbatim rather than extending it.

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?

With no output schema, the description fully compensates by listing the returned fields (block number, base fee, priority fee, gwei price, 21k-transfer and 65k-ERC-20 costs) and the payment model. Nothing an agent needs to call this correctly is missing for a single-parameter read tool.

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 `chain` parameter already enumerates every accepted value plus the chain-id alternative, so the description adds nothing parameter-specific. Baseline 3 applies when the schema fully carries parameter meaning.

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 resource (gas price, base fee, priority fee) and scope (EVM chains), and it clearly occupies a niche none of the evm_* siblings fill (balance, tx, token, units, selector). An agent can tell immediately what this tool produces without opening the 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?

Usage is only implied — an agent infers 'call this when you need gas/fee data'. There is no explicit when-to-use framing, no mention of alternatives, and no statement about when this is unnecessary (e.g. historical fee queries are out of scope).

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