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

Goes well beyond the readOnlyHint/openWorldHint annotations: names upstream data sources (mempool.space, Coinbase spot for USD), discloses a 30-second cache TTL that bounds data freshness, and states the exact paid-call model ($0.002 USDC via x402, failed calls not charged). These are precisely the operational facts an agent needs before invoking.

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?

Front-loaded with the returned data and organized logically (outputs, then sources, then caching, then pricing). The payment/legal sentence is long and slightly boilerplate-heavy, but each clause still carries distinct 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 parameters and an output schema already available, the description fills exactly the remaining gaps: data provenance, freshness guarantee, and cost per call. Nothing an agent needs in order to decide to call it and interpret the result 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?

The tool takes zero parameters, so the baseline is 4 and there is nothing for the description to clarify. The description correctly documents none are required and instead spends space on the shape of the response.

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?

States a specific resource (Bitcoin fees in sat/vB) and enumerates exactly what comes back: fee tiers (fastest/30m/1h/economy/minimum), mempool size and count, and a 140 vB transaction cost in BTC and USD. This is clearly distinguishable from EVM-oriented siblings like gas or defi_fees without opening any 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?

The enumerated outputs imply when the tool is relevant (fee estimation, mempool congestion checks), but there is no explicit when-to-use or when-not-use statement, and no named alternative among the many crypto siblings. The 'Information only, not financial advice' line is a disclaimer, not usage guidance.

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