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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint=false. The description adds important context beyond annotations: it is a paid call, the price is 5 sats or US$0.005, and it lists the returned block and histogram fields. It does not cover rate limits or error behavior.

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 description is information-dense and front-loads the main purpose before listing returned fields and payment terms. The long field list is justified by the lack of an output schema, though the prose is dense.

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?

There is no output schema, so the description carries the burden of explaining return values, and it does so by naming the next-4-block metrics and whole-mempool histogram. It also includes payment cost and payment options, making it sufficiently complete for this tool.

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 optional parameters (l402 and pay_with) are already documented in the schema. The description only implies paid access and does not add parameter-specific semantics beyond what the schema provides.

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 states a specific verb and resource: projected next Bitcoin blocks from the live mempool. It also enumerates the exact per-block metrics and fee histogram, making the tool's purpose clearly distinct from sibling fee and status tools.

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 'live mempool' and 'next 4 blocks', which signals next-block fee planning. However, it does not explicitly say when to use this instead of siblings such as bitcoin_fee_estimates or bitcoin_fee_history.

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