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

Annotations already declare the operation read-only, idempotent, and non-destructive. The description adds meaningful behavioral context by revealing that this is an external ABR web-service lookup requiring a user-supplied GUID, which is not obvious from annotations alone. It also discloses the kind of data returned without contradicting any annotation.

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 description is compact and front-loaded, covering purpose, return fields, prerequisite, registration link, and an example in a short space. The 'BYOK' abbreviation is jargon but is immediately clarified by the next sentence. Overall, every sentence contributes meaningful value.

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 two-parameter read-only tool with no output schema, the description is self-sufficient: it lists the main return fields, states the external dependency and key requirement, gives the registration URL, and provides a complete invocation example. An agent has enough context to select and call 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?

Schema description coverage is 100%, with detailed descriptions for both abn (format, spaces, example) and _apiKey (GUID, registration link). The description reinforces _apiKey's role and provides an example, but adds little semantic information beyond what the schema already provides. 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?

The description uses a specific verb and resource: 'Look up an Australian Business Number (ABN)', then enumerates the exact returned fields (legal entity name, entity type, ABN status, GST registration, address, business names). This clearly distinguishes it from siblings such as abn_search (search vs lookup by number) and acn_lookup (different identifier type).

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 clearly establishes when to use this tool: when you have an ABN and want entity/business registration details. It also communicates the BYOK prerequisite, the required _apiKey, and where to register for one. It does not explicitly name alternatives or exclusions, but the usage context is clear.

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