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

Annotations already cover read-only, idempotent and open-world behavior, so the bar is lower, and the description still adds material context: a daily per-caller free quota and the fact that payment headers (X-Payment / X-Payment-Tx / Bearer fg_…) belong in the MCP request headers rather than the arguments. It also discloses that only two fields come back, which matters because there is no output schema. It does not describe failure modes when the quota is exhausted.

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 useful routing information is front-loaded, but the same content is stated twice in Chinese and English and padded with vendor framing text ('供应方资产', 'Vendor asset'). Several sentences repeat the free-tier scope rather than adding information, so the definition is longer than its payload warrants.

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 parameters and no output schema, the description carries the burden of explaining the return shape and does so (top 5, symbol and USD price only), plus quota and auth placement. An agent can call it correctly from this text. The remaining gap is minor: nothing about ordering or what happens at quota exhaustion.

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 tool takes zero parameters, which is the baseline-4 case, and the description confirms this explicitly with 'Args: none' / '入参：无'. No misleading parameter hints are introduced.

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 names the resource (top coins by market cap) and specifies exactly what the free tier returns: top 5 symbols plus USD price. It also names the sibling that covers the fuller dataset (top100_full), so the agent can distinguish the two. It stops short of a crisp single verb statement because the intent is embedded in a quoted user question rather than stated declaratively.

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?

It gives an explicit routing rule: use this call to confirm the market-cap convention with a 5-coin sample, and go to top100_full for the full 100 with market cap, 24h volume, 24h change, circulating supply and ATH distance. That is a clear alternative with its selecting condition. It does not state when-not to use it beyond that tier split, but the alternative is unambiguous.

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