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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description adds genuinely useful behavior beyond that: a 15-second cache window and a $0.005 per-call cost paid via x402 in USDC on Base or Solana. It still says nothing about freshness risk beyond the cache or what the returned fee data looks like.

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 short fragments with the purpose front-loaded and no filler; caching and price are the two facts an agent most needs. The parenthetical 'x402: USDC on Base or Solana' is dense jargon that could be clearer, which keeps it from a 5.

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 simple one-parameter read tool this covers purpose, cache, and cost, but with no output schema the description should say what is actually returned (gas price units, chain breakdown, fee tiers) and it does not. The payment flow implied by x402 is also only hinted at.

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 optional `tx` parameter is documented in the schema as an alternative to the X-Payment-Tx header. The description's x402/USDC note gives some surrounding context for the payment path but does not explain the parameter itself, so baseline 3 is right.

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?

Names the specific resource (network fees) and the two chains covered (Ethereum, Solana), which is enough to distinguish it from siblings like price, token_price, or market_overview. It does not explicitly route against any sibling, so it falls short of a 5.

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?

There is no statement of when to use this tool versus alternatives such as price or market_overview, and no prerequisites or exclusions. Only billing mechanics are mentioned, which is not usage guidance.

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