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

Annotations alone would look odd for a data fetch (readOnlyHint=false, idempotentHint=false); the description resolves this by disclosing the x402 payment model, cost ($0.002 USDC on Base), and that billing is per successful call. Return format is not described, but an output schema exists, so that gap is acceptable.

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?

Two sentences, front-loaded with what is returned, then usage, then the cost disclosure. No filler; every clause carries information an agent needs.

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 0 params, an output schema for return values, and annotations covering the safety profile, the description supplies the remaining essentials: usage trigger and the paid-call cost model. Nothing required to invoke it correctly is missing.

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?

Zero parameters, so baseline is 4. There is nothing for the description to disambiguate, and it correctly avoids inventing parameter 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?

Specific verb+resource: it enumerates exactly what the call returns (next-block/half-hour/one-hour/economy sat/vB rates, cost in sats of a typical payment, mempool size, pending fees, latest block height). This clearly distinguishes it from siblings like btc_price or btc_address even without opening a schema.

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?

Explicitly says when to use it: 'before sending a Bitcoin transaction or to decide whether to wait for lower fees.' That is concrete decision context, though it names no alternative tool (e.g., other gas/fee siblings) or when-not-to-use case.

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