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

With no annotations, the description carries the full burden and does well: it discloses the venue coverage, the limits of 24h history (only Binance and Bybit), and the commercial model ($0.003 USDC per call via x402 on Base), which is critical pre-invocation context an agent would otherwise not know. It stops short of error behavior or rate limits, 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?

A single dense sentence that front-loads the resource and appends cost last, with zero filler. It is slightly overloaded with parenthetical venue lists, but every clause carries 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?

For a one-parameter tool with no output schema and no annotations, the description covers what is returned, which venues, where history is missing, and the payment requirement. Only invocation-failure and pagination/format details are absent, which is a minor gap at this complexity.

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?

Only one parameter and schema coverage is 100%, with the schema already supplying the 'BTC, ETH, SOL' example. The description adds nothing about symbol format (case sensitivity, perp-specific suffixes, quote asset) beyond what the schema states, so the 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 resource (open interest of a coin's perpetual) and enumerates the venues plus the exact metrics returned (contracts, USD, market share, 24h change, long/short ratio). An agent can distinguish this from perps_funding or perps_extremes by the data returned, though the description never names those siblings explicitly.

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?

There is no when-to-use guidance and no alternatives are named, even though perps_funding and perps_extremes sit in the same family. The only conditional statement — '24h change where history exists (Binance, Bybit)' — is a data-availability caveat, not usage direction.

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