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

Annotations only declare readOnly and openWorld; the description adds genuinely new operational facts: exact price ($0.001 USDC per successful call), payment rail (x402 on Base, Solana or Arc), and that failed calls are not charged. It also discloses the model's accuracy limit, which is behaviorally important for interpreting results.

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?

Four compact sentences, each carrying distinct information (outputs, coverage, method, exclusions, pricing). Front-loaded with what is returned and for which chains. Slightly dense with parentheticals, but nothing is wasteful.

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?

Output schema exists so return shape needs no description; the description covers chains, defaults, forecast limitations, cost, and payment mechanics. For a single-optional-parameter priced data endpoint, an agent has everything needed to call it and budget for it.

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 documents 'ethereum, base or arbitrum (default ethereum)'. The description restates the same enumeration and the Solana exclusion but adds no format or casing guidance beyond the schema, so this is baseline territory.

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 resource (base fee and priority-fee percentiles at 10th/50th/99th) and the exact chains covered, plus the projection method (EIP-1559, next block from last block fullness). An agent can immediately tell this is a gas-fee oracle rather than any other onchain metric tool in the sibling list.

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?

Explicitly bounds scope by excluding Solana ('Solana is not included here') and clarifies that forecasts are a one-block projection, not a congestion model — effectively telling the agent when not to rely on it for trend analysis. It does not name an alternative sibling for Solana gas data, so it stops short of full routing guidance.

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