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

With no annotations, the description carries the full disclosure burden and does well: it declares the cost tier, names the algorithm, and explicitly states what is NOT verified (branch against the Payments NZ register). It omits auth/rate-limit behavior, but the key correctness caveat is disclosed up front.

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?

Two tight sentences with no filler; the scope limitation is front-loaded immediately after the purpose statement. Every clause carries information an agent needs.

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 not be described, and the checksum-vs-register caveat is present. However, for a 2-parameter validator with no annotations, the missing account-format guidance and unexplained jurisdiction parameter leave the definition meaningfully short.

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% for 2 parameters, so the description must compensate. It never mentions the expected account format (e.g. bank-branch-account-suffix) or explains the unexplained 'jurisdiction' parameter with its default of NZ on an explicitly NZ-only tool — leaving both inputs ambiguous.

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 resource ('check an NZ bank account number') and names the exact algorithm applied, which is far beyond a tautology. It is distinguishable from validate_ird and validate_abn by resource, though it never explicitly says 'this is not the IRD number tool' — a real risk given the oddly overlapping 'Inland Revenue algorithm' phrasing.

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 'Free:' prefix implies a paid tier exists and thus a usage context, and the checksum-only statement hints at when the tool is sufficient. But there is no explicit when-to-use routing against siblings like validate_ird, nor any statement of when a paid/full-register check is required instead.

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