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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered; the description goes further by disclosing the concrete billing model ($0.002 USDC per successful call via x402 on Base/Solana/Arc, failures not charged) and the derived-metric basis ('from the 20 returned levels per side'). Cost-per-call is exactly the kind of behavior an agent needs before deciding to invoke, and it is not expressed anywhere in structured fields. It does not cover freshness/latency or whether levels are truncated, so not 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 compact sentences, front-loaded with the resource and scope, then the field inventory, then the commercial terms. Every clause carries information an agent would otherwise have to discover — no filler, no 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?

With an output schema present the description need not explain return structure, yet it names the key metrics anyway so a caller can judge relevance before spending $0.002. Scope limit, data provenance (20 levels per side), and payment mechanics are all covered for a one-parameter read tool.

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?

There is a single parameter with 100% schema description coverage including inline examples ('BTC, ETH, SOL'), so the schema already carries the semantics. The description adds only the ordinal constraint 'for one coin,' which confirms the parameter is single-valued but adds no syntax or validation detail. 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?

The description states a specific verb and resource — a Hyperliquid L1 perpetual market snapshot for a single coin — and enumerates exactly what comes back (best bid/ask, spread, 1% depth, mark/oracle, hourly funding, OI, 24h volume). That level of enumeration distinguishes it from generic orderbook tools like crypto_binance_orderbook_depth or crypto_coingecko_market_depth without naming them. It stops short of an explicit 'not this sibling' routing statement, so it lands at 4 rather than 5.

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?

Usage context is implied by 'perpetual market snapshot for one coin' and the explicit scope exclusion 'public market data only; vault PnL is not included,' which tells the agent not to reach for it for vault analytics (a real sibling concern, e.g. crypto_gmx_v2_glv_vaults). However, there is no explicit when-to-use clause, no mention of when a sibling like finance_hyperliquid_perp_funding or a depth tool is the better pick. Adequate but leaves routing to inference.

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