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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so the safety profile is covered. The description goes further by disclosing the actual algorithms and the domain caveat that bitcoin mode is for block-data checking only, which is real behavioral context an agent could not derive from annotations. It does not mention determinism/ordering guarantees for documents mode, so it is not a 5.

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 opening two mode sentences are dense, front-loaded and earn their place. The trailing three sentences ('Put tool fields inside inputs', 'Follow its required fields and exact choices', 'Do not pass the REST calculator field...') are generic boilerplate that restates schema constraints and dilutes the useful content.

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?

An output schema exists, so return values need no explanation, and annotations cover the safety profile; what remains is domain semantics, which the description supplies for both modes. It is slightly incomplete in omitting leaf ordering expectations and the maxItems=128 limit for a tool that hashes up to 128 items.

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 0%, so the description must carry parameter meaning; it does explain that 'leaves' means SHA-256 fingerprints in documents mode and display-order txids in bitcoin mode, and that mode defaults to 'documents'. It adds nothing about the 1-128 leaf bound, ordering sensitivity, or the modelVersion parameter, which is only obliquely covered by 'Supply units or modelVersion only when listed in inputSchema'.

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 precisely what is computed (a Merkle root) and enumerates two concrete modes with the exact hashing scheme for each (RFC 6962 leaf/node prefixes vs. Bitcoin double SHA-256 over display-order txids). An agent knows exactly which resource and transformation it gets. It stops short of naming or contrasting the sibling buscalc_chain_merkle_verify, so the compute-vs-verify distinction must be inferred from the name alone.

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?

It gives one genuine routing signal: mode 'documents' is the default and 'bitcoin' is 'for checking block data only', implying the latter is a narrower verification use case. However, it never states when to call this instead of merkle_verify, nor any prerequisites such as leaf ordering requirements for documents mode.

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