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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds genuinely non-obvious behavior: a free tier with a daily per-caller quota, and the requirement that payment credentials travel in MCP headers (X-Payment / X-Payment-Tx / Authorization: Bearer fg_…) rather than as parameters — a real caller trap it pre-empts.

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?

The same payload is stated three times: the English opener, the [zh] line, and the [en] line all convey 'free, returns perp positioning, arg is symbol'. Front-loading is good, but the tri-lingual duplication and boilerplate asset title add substantial length without new 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?

With no output schema, the description is the only source of return values, and it does name the metrics and the two conclusion labels — enough to know roughly what comes back. However, it omits the symbol format and gives no sense of the response envelope (e.g., field names for the labels), leaving gaps for a one-required-param snapshot 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?

Schema description coverage is 0% for the single parameter, so the description must carry format meaning. It only restates that symbol is required ("参数 symbol 必填" / "Args: symbol") — no format hint such as BTCUSDT vs BTC, no case sensitivity, no accepted market suffix. That is repetition of the schema's required list, not added semantics.

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 frames the tool with a concrete question ("how are perpetual traders positioned") and enumerates exactly what it returns — 24h OI change, long/short account ratio, taker buy/sell ratio, plus two labels (positioning / taker_flow). That is a specific resource and metric set. It never contrasts itself with the sibling perp-positioning.positioning, so it falls short of a 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 is only implied through the motivating question ("Ask how are perpetual traders positioned"); there is no explicit when-to-use, when-not-to-use, or named alternative such as perp-positioning.positioning. The free-tier/quota note is an operational constraint rather than selection guidance.

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