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

Annotations only say non-read-only, open-world, idempotent. The description adds genuinely new behavior: a trust assumption ('Verify against a trusted header chain') and a cost model ('20 sats or US$0.02 (USDC) per call'), both of which change how an agent should invoke and budget this. No conflict with readOnlyHint=false, since the call is paid and produces an artifact.

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?

Five short front-loaded statements: purpose, locator format, trust model, limitation, price. No filler, no restatement of the title, and the highest-value constraints come first.

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 and full schema coverage, the description only needs purpose, trust model, guarantees, and cost — all delivered. The one open thread is how the 'trusted header chain' is obtained or supplied, which an agent may still wonder about.

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 coverage is 100%, so the baseline is 3; the description adds a compact locator grammar ('blockhash:txid[,txid...]') and the 'retained block' constraint that the schema prose only implies. It says nothing about l402 or pay_with semantics, leaving those entirely to the 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?

States a specific verb and artifact ('Generate a verified Bitcoin Core Merkle inclusion receipt') plus scope ('one to five transactions in one retained block'). The locator notation makes the resource identity unambiguous, so an agent can tell this apart from the sibling risk/analysis tools 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 bounds the use case tightly (one block, 1-5 txids) and states what the result does NOT cover ('Does not establish unspentness or irreversible finality'), which helps an agent decide this isn't a settlement/finality check. It never names an alternative sibling or a when-not-to-call condition explicitly, keeping it short of a 5.

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