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

Annotations already cover read-only, open-world, and idempotent safety, so the description only needs to add non-obvious traits. It adds the per-call cost ($0.001 USDC), the mempool.space source, and byte-identical equivalence to the REST endpoint. This is useful beyond the annotations, though it omits potential rate-limit or freshness details.

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 two sentences and front-loads the core output and use case. The second sentence adds cost and endpoint equivalence without padding. No words are wasted.

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 an output schema present, return-value details are already covered. The description covers purpose, source, cost, and liveness use case, which is everything needed for a zero-parameter read-only tool. It is complete for correct invocation.

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 has zero parameters and an empty input schema, so there are no parameter semantics to document. Per the rubric, a zero-parameter tool gets a baseline of 4. The description makes no parameter claims, which is appropriate.

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 exactly what the tool returns: the current Bitcoin block height and the best tip hash, with source attribution to mempool.space. It also characterizes the tool as a 'two-second liveness check,' clearly distinguishing it from the many market_btc_* siblings. This is a specific verb/resource definition that an agent can act on without opening the 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 description explicitly frames the tool as a liveness check for Bitcoin-facing operations, giving a clear when-to-use context. It does not name sibling alternatives or exclusions, so it stops at clear context without full when-not guidance. Cost and API equivalence further help an agent decide to call it.

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