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

Annotations already carry readOnly/openWorld/non-destructive, but the description adds critical non-annotation behavior: a $0.002 USDC per-call cost, the x402 payment rails (Base, Solana, Polygon, Arbitrum), and that x402 MCP clients pay automatically. That payment disclosure is exactly the kind of context annotations cannot express. It stops at 4 because error/rate-limit behavior and failure modes are not addressed.

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-loaded with the mode breakdown, then params, then pricing, and the free-sample call at the end is a practical touch. It is a dense single block rather than bulleted, which slightly hurts scannability, but every sentence carries information.

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 correctly picks up the burden by describing what each mode returns (TVL plus 1d/7d change, category, market cap, chain breakdown; volume windows and top DEXes). Combined with full param coverage and payment details, an agent has enough to call it correctly.

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?

With only 60% schema coverage, the description compensates well: it explains all four mode values, gives concrete examples for protocol ('aave, uniswap, lido'), category, and chain, restates the limit range, and clarifies the non-obvious default logic. It adds real meaning beyond the enum-only schema for mode.

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 verb+resource ('DeFi data from DefiLlama') and enumerates the four distinct data products (protocol TVL, top protocols, chain rankings, DEX volume), so an agent knows exactly what it returns. It does not, however, name or contrast with the closest sibling defi_yields, so it stops short of full sibling differentiation.

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?

Each mode is given a use case and example filters ('category (e.g. Lending, Dexs...)', 'optionally for one chain'), and the default-selection rule ('default top, or protocol if protocol is given') tells the agent how to invoke it without specifying mode. There is no explicit when-not-to-use or pointer to a sibling like defi_yields.

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