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

Goes well beyond the read-only annotations with a concrete failure mode ('A feed outage reads as unknown, never a healthy peg'), the pricing/access model (x402 $0.01, prepaid x-credit-token header, 1 free call/day, no API key), and the key insight that depegs are silent. This is exactly the behavioral context annotations cannot carry.

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 core question then the scope, and information-dense. Slightly padded by the rhetorical opener, the 'Not financial advice' disclaimer, and the payment boilerplate, though each is arguably necessary for an x402-priced tool.

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?

Covers purpose, scope, failure handling, and access model; since an output schema exists, return-value detail is unnecessary. Nothing an agent needs to call this correctly is missing.

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 param is self-documenting, so the baseline is 3. The description adds value by enumerating the supported coin set and restating single-coin vs all-coins behavior, giving meaning beyond the bare 'One stablecoin (optional, default all)'.

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 and resource ('Live DEX price vs the $1.00 peg for major USD-pegged stablecoins on Base') with named coverage (USDC, USDT, DAI, USDbC). An agent can tell this apart from cap/supply siblings like stablecoin_mcap or b20_stablecoin without opening a schema.

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?

Explains the triggering scenario well ('an agent parked in stables reprices everything off a stale $1') and how to narrow to one coin ('Pass symbol= for one coin'). It does not explicitly name an alternative tool or a when-not-to-use condition, so it falls short of a 5.

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