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

Annotations already declare readOnly, idempotent and open-world, so the safety profile is covered. The description adds real value beyond them by naming the validation method (mod-89 checksum) and disclosing that a signed XDR-1 receipt is produced, though it does not say what happens when the checksum fails.

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?

Three short sentences, front-loaded with purpose, then obligation, then output. Nothing is redundant or buried.

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?

Output schema exists so return values needn't be explained, and annotations cover safety; the description supplies purpose, algorithm and use context. The one remaining gap is failure semantics — whether an invalid ABN yields a false result, an error, or a rejected receipt.

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 100% and the single `abn` parameter is fully documented in-schema, including spacing rules. The description's "(11 digits)" merely restates the schema rather than adding format or parsing meaning, so baseline 3 applies.

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 (Validate), resource (Australian Business Number), and the exact algorithm (mod-89 checksum, 11 digits), which cleanly separates it from siblings like vat_mod97_check or gstin_check that validate other identifier schemes.

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?

"Required before invoice payment to Australian contractors" gives a concrete triggering context for use, but no explicit when-not condition or named alternative for non-Australian vendors (e.g. gulf_supplier_check, china_supplier_check).

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