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

Beyond the readOnly/openWorld hints, it discloses the data provenance (DefiLlama public API), the exact price ($0.002 USDC per successful call via x402 on Base, Solana, or Arc), and the billing rule that failed calls are free. That is precisely the kind of cost and failure semantics an agent cannot infer from annotations.

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 the metric/chain/unit, then the disambiguation, then pricing. No filler and nothing buried.

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-optional-parameter read tool with an output schema and readOnly annotations, everything needed to call it correctly is present: source, unit, granularity, range, and cost. Minor omission is what happens for out-of-range `days` values or how payment settlement is triggered, but nothing blocking.

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%, so the single `days` parameter (range 1–30, default 7) is already fully documented. The description adds only the granularity notion ('daily history'), which is a small marginal gain over the schema; baseline 3 applies.

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 a specific metric (GMX total value locked), a specific chain (Arbitrum), a specific unit (USD), and a specific source (DefiLlama), plus the scope of output (current value plus 1–30 days of daily history). It also pre-empts the most likely confusion by stating this is not GMX trading volume or fees.

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 final clause explicitly excludes the two nearest alternative metrics (trading volume, fees), which tells an agent when this tool is not the right one. It does not name a concrete sibling to route to instead, so it stops short of full when/when-not/alternatives coverage.

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