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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), and the description adds real behavioral detail beyond them: the exact hash construction per variant, that RFC 9162 inclusion checking runs from leafIndex/treeSize, and that unsupported formats are refused rather than coerced. It says nothing extra about failure modes such as malformed proof length or mismatched root, but the output schema covers return shape.

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 first three sentences are dense, front-loaded, and earn their place. The closing boilerplate ('Put tool fields inside inputs', 'Follow its required fields and exact choices') is generic wrapper text that adds no tool-specific value, and the 'units' reference is a mismatched artifact from a template.

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?

For a nested, six-field proof object with two enum-constrained discriminators, the definition explains construction semantics, the inclusion-check inputs, and the optional trust anchors — enough for an agent to build a valid call. The remaining gap is the absence of guidance versus sibling verification tools, not missing mechanics.

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 carries the load, and it does add meaning the schema cannot: what 'rfc6962' versus 'bitcoin' actually certify, and that document_sha256/expected_root are optional cross-checks. The trailing 'Supply units or modelVersion only when listed in inputSchema' is generic scaffolding, and 'units' is not even a parameter of this tool.

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 opening sentence gives a specific verb+resource ('Verify a BusCalc Merkle proof bundle') plus the accepted format identifier, which is far more informative than the title 'merkle verify'. It is clearly a proof-verification tool rather than root computation, though it never names siblings like buscalc_chain_merkle_root or buscalc_verify_record_proof to draw the boundary explicitly.

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 states hard preconditions — only format 'buscalc-merkle-proof/2' with construction 'rfc6962' or 'bitcoin' is accepted, anything else is refused — and notes that root/txid comparison is optional. It gives no guidance on when to pick this over the sibling verification or merkle_root tools, so routing is left to inference.

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