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

Annotations cover the read-only/destructive profile, and the description adds what they don't: the upstream source ('Hyperliquid's public API'), the 500-hour lookback cap, and a detailed cost model ($0.01/call, first 25 free, failed calls free, repeats charged). The 'each call is charged, so repeats are not free' line is consistent with idempotentHint=false.

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?

The core capability and return shape lead, followed by usage and cost; nothing is buried. The pricing/payment sentence is dense boilerplate but does carry decision-relevant cost information.

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?

No output schema, but the description fully describes the return payload (per-rate fields plus aggregate average and APR), the data source, the history cap, and the cost model — everything an agent needs to call and interpret 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?

Schema coverage is 100% with both parameters documented (coin default ETH, hours 1-500 default 24). The description restates the example coin=ETH and the default window but adds no syntax or edge-case meaning beyond the schema, so baseline 3 applies.

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: 'Past hourly funding rates of a Hyperliquid perpetual', and enumerates the return contents (rate, premium, time, average rate, APR). It also explicitly disambiguates from the sibling hyperliquid_market, which serves the current rate.

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?

Names concrete use cases ('compare carry over time, spot funding regime changes, or backtest basis and funding-arbitrage strategies') and gives an explicit exclusion redirect: 'for the current rate use hyperliquid_market'. Window bounds and default are also stated.

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