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

Annotations already establish the tool is read-only, idempotent, and non-destructive. The description adds behavioral transparency beyond that by revealing accepted symbol formats ('MASKUSDT', 'MASK', 'MASK-USDT-SWAP') and the output fields (contracts outstanding, coin size, USD notional, timestamp). It does not contradict 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 sentences, each earning its place: the first defines the data returned, the second gives input examples, the third states a use case. No filler or repetition.

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 no output schema, the description covers the return fields explicitly. It also handles the primary input ambiguity (instId format). It omits details like default instType behavior (already in schema) and possible time ranges or historical depth, but for a simple snapshot tool this is sufficient.

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?

The schema only describes instType, leaving instId as a bare string. The description compensates for this gap by giving concrete example formats and clarifying that these map to perps or futures. This adds meaningful guidance beyond the schema's 'string' type, although it does not exhaustively define all possible instId formats.

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: it retrieves open interest for crypto perpetual swaps or dated futures contracts on OKX. It also lists the exact return contents (contracts outstanding, coin-denominated size, USD notional, timestamp), making the purpose unmistakable and distinguishing it from other market data tools like order_book or funding_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?

The description provides explicit context for use ('Use to size how much leverage is riding on a perp'), which guides when to invoke it. However, it does not name alternatives or give explicit when-not-to-use conditions, so it stops short of full discriminative guidance.

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