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

Annotations already cover the safety profile (readOnlyHint, openWorldHint), yet the description adds genuinely new context: the upstream source (Hyperliquid public info API), the per-call cost ($0.002 USDC), the payment rails (x402 on Base, Solana or Arc), and the billing rule that failed calls are free. It stops short of rate limits or latency/caching behavior.

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 sentences with zero waste: the first front-loads what the call returns and its source, the second carries the billing terms. Nothing is repeated and no filler precedes the substantive content.

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 an output schema present, return values need not be re-explained, the single required parameter is fully covered, and the payment model is disclosed – so an agent has what it needs to call correctly. Minor gaps remain around data freshness (live snapshot vs point-in-time) and rate limits.

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 schema already documents the coin parameter with the same BTC/ETH/SOL examples the description gives, so the description adds no format, casing, or lookup semantics beyond it. Baseline 3 applies when the schema carries the parameter burden.

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 ('Hyperliquid perpetual futures snapshot for one coin') and enumerates exactly what is returned: mark, oracle and mid price, hourly funding rate, open interest, 24h volume. This field list implicitly separates it from siblings like crypto_hyperliquid_perps_depth, since an agent can tell this is a funding/mark snapshot rather than an order book.

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?

The 'one coin (e.g. BTC)' phrasing implies the single-coin scope of use, but there is no explicit when-to-use, when-not-to-use, or named alternative among the many sibling ticker/oracle tools. Usage must be inferred from the payload list rather than stated.

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