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

Annotations already declare readOnly, openWorld, idempotent and non-destructive, and the description goes further by disclosing the commercial model: 10 free calls/day, then $0.001/call via x402 (naming the exact _meta key) or X-API-Key credits. That is precisely the auth/rate-limit context an agent needs before deciding to call, and the fee-scope caveat adds another behavioral constraint.

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?

Front-loads the payload (what fees, for which scenarios) before pricing and provenance, so an agent can stop reading early if it only needs to know the capability. The payment sentence is dense but each clause is actionable; the trailing '[served by ...]' host tag is mildly extraneous.

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 one-parameter, default-everything read tool with an output schema, the description covers capability, coverage caveat (on-chain fees only), chain selection behavior and cost/auth mechanics. Nothing an agent needs to invoke it correctly is left unstated.

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 description coverage is 100% and the single `chains` parameter already documents the comma-list format and the all-7 default, so the description adds essentially nothing about parameter syntax. Baseline 3 applies since the schema carries this burden fully.

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 concrete resource (gas on 7 EVM chains) and enumerates the exact metrics returned: base fee, priority fee, suggested maxFee, plus native-token cost for transfer, ERC-20 transfer, approve and DEX swap. The added claim that it names the cheapest ETH-gas chain for a typical swap further sharpens what this tool uniquely delivers versus a generic chain lookup.

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?

Gives clear usage context through the enumerated fee scenarios and the implied default of all 7 chains, and the 'on-chain fees only, no USD conversion' note tells the agent when the output is insufficient. However, it never names an alternative tool or states when not to call it, so the routing guidance is informative rather than directive.

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