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

Annotations already establish read-only, idempotent, closed-world behavior, so the description's main added value is the payment contract: cost of 3 sats / US$0.003 per call and the data provenance ('Bitcoin Core estimatesmartfee on this node'). It does not describe what an unpaid call returns (e.g., a 402 challenge), which the schema only hints at via the l402 parameter.

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 and the confirmation-target list; the price is placed last where it belongs. The nine-number block list is dense but each value conveys real 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 carries the burden of describing returns, and it does: per-target sat/vB values, mempool size, and minimum relay fee. Combined with the schema's payment parameters and the annotations' safety profile, an agent has enough to call this correctly and interpret the result.

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 100%, so both l402 and pay_with are already documented in the parameter descriptions. The description adds nothing about either parameter, leaving it at the baseline for a fully described schema.

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-and-resource: it returns current Bitcoin fee estimates in sat/vB for nine named confirmation targets, plus mempool size and minimum relay fee. The 'right now' framing and the estimatesmartfee source make it distinguishable from the historical/ETA siblings, though it never names bitcoin_fee_history or bitcoin_transaction_eta directly.

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 implied by 'right now' and the explicit per-call price, which tells the agent this is a paid, point-in-time lookup. There is no statement of when to prefer it over bitcoin_fee_history (historical), bitcoin_transaction_eta, or bitcoin_mempool_blocks, so routing still requires inference.

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