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

With no annotations, the description carries the full burden and does well: it discloses that the call is paid, the exact price and payment chain, that no auth is needed, and that failures are not charged — all behaviors an agent cannot infer from schema. It omits response shape (JSON vs text), latency, and whether prices are cached or real-time.

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 single most decision-relevant word ("Paid") before the payload, then cost, then access terms, ending with the endpoint URL. Sentence-fragment style is dense but every clause carries information; a slightly less telegraphic phrasing of the field list would read better.

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 supplies the return contents inline, plus cost, payment rail, auth requirements, failure billing, and data provenance. For a zero-parameter paid price lookup, an agent has everything needed to decide and call it.

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?

Zero parameters and 100% schema coverage, so there is nothing for the description to disambiguate. Baseline 4 applies; the description correctly spends no words on parameter semantics.

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 the exact resource (POWR/USD live price) and enumerates the returned fields: last price, 24h open/high/low, % change, 24h and 30d volume. It also names the data sources (Coinbase Exchange with Kraken cross-check), so the agent knows precisely what it gets and can distinguish it from the ~400 sibling buy_coin_* tools purely on asset symbol.

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?

"Paid" plus "$0.05 USDC on Base. No account, no API key. Failed calls not charged." gives clear preconditions and cost, which is real usage context. It stops short of naming an alternative (e.g. buy_crypto_price or buy_coin_00) or stating when a different price source is preferable.

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