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

Beyond the readOnlyHint/openWorldHint annotations, the description discloses the cost model ($0.002 in USDC per successful call), the payment rail (x402 on Base, Solana or Arc) and the billing edge case (failed calls are not charged). This is exactly the kind of economic and side-effect 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?

Two tightly packed sentences, front-loaded with what the tool returns before the payment terms. No filler and nothing an agent needs to skip past to reach the operative facts.

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 a full input schema, an output schema, and annotations covering safety, the description covers the remaining gaps: data source, returned fields, and payment mechanics. The only omission is error behavior for an unknown or malformed symbol, a minor gap for a simple single-parameter read.

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% with a single required 'symbol' parameter that already documents ticker examples, so the schema does the heavy lifting. The description reinforces the single-symbol constraint ('one asset symbol') but adds no format, casing, or validity guidance beyond the schema.

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?

The description states a specific verb and resource ('current USD price for one asset symbol... from DIA's public quotation endpoint') and even names the extra data returned (yesterday's price and volume). It does not, however, differentiate itself from the many other price-oriented siblings (crypto_pyth_network_oracles, crypto_chainlink_price_feeds, finance_coingecko), so the agent must infer the distinction from the DIA brand alone.

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?

Usage is implied rather than stated: 'one asset symbol' signals a single-asset lookup and nothing else. There is no explicit when-to-use/when-not or comparison against alternative price sources, so an agent cannot tell from the text alone why it should pick DIA over Chainlink or Pyth.

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