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

Annotations already cover the read-only, idempotent, non-destructive profile, but the description adds information the annotations cannot: a per-caller daily quota on the free tier, and the exact auth mechanism (X-Payment / X-Payment-Tx / Authorization: Bearer fg_…) with the explicit warning not to put payment data in parameters. That auth placement guidance is genuinely valuable and prevents a common misuse. What is missing is any statement of what happens on quota exhaustion or how a caller obtains a payment token.

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 English lead sentence is well front-loaded and does the real work, but everything after it is near-duplicate restatement across zh/en blocks — the activity metrics are listed three times and 'free, args: days' appears twice. The payment-header note is useful but buried at the end rather than structured as a distinct prerequisite.

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 one optional parameter and no output schema, the description does its duty by naming the return fields (trend, tx count, active addresses, delta vs mean) and documenting the auth/quota envelope. A caller knows what it will get and how to pay for it. The only gap is behavior on quota exhaustion or invalid `days`.

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 coverage is 0% and the single `days` parameter has only a null default, so the description carries the burden. It does add meaning by calling `days` the 'window length' (窗口长度) and marking it optional (可选), which tells the agent this is a lookback window rather than a calendar parameter. It stops short of giving format or units (e.g., whether 7 means seven days) or the behavior when omitted.

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 opening sentence names a concrete verb and resource ('how active is the Bitcoin network') and enumerates the returned metrics: activity trend, tx count, active addresses, and change vs mean. It does not explicitly contrast with the sibling btc-onchain.btc_onchain_full, though the repeated emphasis on 'free tier' (免费档) hints at a paid counterpart without naming it.

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 framing question 'ask how active is the Bitcoin network' gives an implied usage context, and the free-tier framing signals this is the lightweight option. However, there is no explicit 'use this when X, use btc_onchain_full when Y' routing, and the daily quota is mentioned without saying what happens when it is exhausted.

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