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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds valuable non-obvious behaviors: the $0.001 USDC per-call cost, the byte-identical relationship to a GET endpoint, and the fact that the order count is opaque. No contradictions with annotations.

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 lean sentences: first describes the output content, second states cost, third anchors the tool to its REST equivalent. Each sentence carries independent value and the most identifying information is front-loaded.

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 one-parameter, read-only snapshot tool with a full input schema, rich annotations, and an output schema present, the description covers all non-obvious context: data contents, per-call cost, and exact REST identity. Nothing an agent needs to invoke it 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 description coverage is 100% and the lone 'coin' parameter is documented with examples (BTC, ETH, HYPE, kPEPE) and a note that it follows Hyperliquid meta naming. The description's 'for one perp' slightly reinforces the parameter's role but adds no meaning beyond what the schema already provides, so a baseline 3 is appropriate.

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 resource (Hyperliquid's l2Book for one perp), the exact fields (resting bid/ask levels with price, size, opaque-order count, and book time), and names the equivalent REST endpoint. This clearly distinguishes it from sibling market_hl_* tools (mid_price, candles, asset_context) and from other exchanges' depth tools (market_gate_depth, market_kraken_depth).

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 description implies when to use it (when you need Hyperliquid's L2 depth snapshot for a single perp) and disambiguates scope with 'one perp', but it never explicitly names alternatives or states exclusions, such as 'for a single mid price use market_hl_mid_price'. The usage context is evident but left to inference.

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