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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds genuine value by specifying the return shape ('as a single number') and by contrasting mark price with oracle price, which is the main semantic trap for this tool. It does not mention error behavior for unknown market symbols, which keeps it short of a 5.

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?

Three tight sentences: the answer shape and coverage first, then the use case, then the disambiguation list. Every clause carries routing or semantic information and there is no redundant restatement 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?

A single required parameter at full schema coverage, an output schema that defines the return value, and annotations covering the safety profile. The description supplies the one thing structured fields cannot: how mark price differs from oracle price and which sibling to pick instead. Nothing an agent needs to call this correctly is missing.

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 market parameter description already enumerates BTC-PERP, xyz:NVDA-PERP, HYPE/USDC, and bare Hyperliquid names. The description reinforces the accepted symbol families but adds no new format, casing, or normalization rules beyond the schema. Baseline 3 applies when the schema does the heavy lifting.

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 ('Latest mark price of one Hyperliquid market as a single number') and immediately enumerates the market families it covers (native perps, HIP-3 builder perps like xyz:NVDA-PERP, spot). The agent can distinguish it from get_mark_prices, get_candles, and get_markets_snapshot without opening any schema.

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?

Gives an explicit selection heuristic ('The quickest answer to what is X trading at') plus three named alternatives with the exact condition that routes to each: get_mark_prices for oracle price and funding, get_candles for history, get_markets_snapshot for multi-market comparison. Nothing is left to inference.

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