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

Annotations already cover the safety profile (readOnly, idempotent, openWorld, non-destructive), and the description goes well beyond them: it discloses error semantics (400 for an unlisted symbol, 503 for a failed read), billing behavior on those errors ('neither is ever billed'), a precise per-call price, and accepted payment rails. That is exactly the operational context an agent needs to decide whether to invoke it.

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?

Four sentences, each carrying distinct information: when to use, what is returned, error/billing behavior, and cost. The use case is front-loaded and there is no padding or repetition of the title.

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 paid, composite read tool with an output schema and full annotations, the description covers invocation context, payload contents, failure modes, and pricing. Nothing an agent needs to call it correctly is missing, and return-value detail is appropriately deferred to the output schema.

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 `symbol` parameter is already documented with an example and a default. The description references the symbol concept only via the error case ('a symbol nothing lists') and adds no format or override guidance beyond the schema, so baseline 3 is correct.

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 resource ('one perp market') and enumerates the payload (Hyperliquid funding, open interest with 1h/24h change, 24h liquidations with long/short split). The phrase 'in a single call' implicitly positions it as the composite snapshot versus single-metric siblings like get_funding_rate or get_open_interest, but it never names those alternatives, so differentiation is left to inference.

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?

'Use when an agent needs one perp market in a single call' is a genuine when-to-use trigger, and the 'single call' framing hints that it consolidates data otherwise spread across siblings. However, with dozens of related perp/funding/OI tools in the namespace, no explicit when-not or named alternative is given, leaving the routing decision implied.

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