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

With no annotations, the description carries the burden of behavioral disclosure. It discloses a key limitation (does not confirm registration), but does not describe the output format (e.g., boolean, error behavior) or edge cases. The behavior is partially transparent but not fully specified.

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 sentences, no fluff. The primary action is stated first, followed by a crucial limitation. All information is essential and front-loaded.

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 simple one-parameter validation tool with no output schema, the description covers the essential purpose and a key limitation. It omits explicit return value behavior, but that is inferable from the verb 'validate'. The description is largely complete for calling the tool correctly.

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?

The schema description already covers the 'acn' parameter fully, including the fact that spaces and hyphens are accepted. The tool description adds no additional parameter semantics beyond what the schema provides. Baseline 3 is appropriate given 100% schema coverage.

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 clearly states the verb 'validate' and the specific resource 'Australian Company Number', and specifies what is validated ('format and checksum'). It also explicitly distinguishes from registration confirmation, which differentiates it from a broader lookup tool and from the sibling validate_abn.

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 implies the tool is for format/checksum validation only, and the caveat 'This does not confirm that the company is registered or active' gives clear context that it should not be used for registration checks. However, it does not explicitly name alternatives or state when not to use it beyond that caveat.

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