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

Annotations already cover read-only, idempotent, non-destructive behavior. The description adds useful context beyond annotations: what data is returned, the source (ABR), and licensing ('free registration, commercial use permitted'). No contradictions with annotations.

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?

Compact and well-organized: purpose, return fields, definition, usage scenario, and source/licensing. Every sentence earns its place with no redundancy or filler; front-loaded with the core action.

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 single-parameter, read-only lookup with an output schema and clear annotations, the description covers everything needed for selection and invocation: what it does, what it returns, when to use it, and access/source context. No critical information is missing.

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 the parameter already describing format, examples, and optional spacing. The tool description reinforces ACN being a 9-digit ASIC-issued number but does not add materially new parameter semantics beyond the schema, so baseline 3 is appropriate.

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 ('Resolve') with a clear resource ('Australian Company Number (ACN) or ASIC-registered number') and states the output entity details. It differentiates itself from siblings by focusing on ACN input, versus ABN or name search tools, and even lists the return fields (ABN, entity name, company type, etc.).

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 explicitly states when to use this tool: 'Use this when you have an ACN from an invoice, contract, or company extract and need to verify the entity against the national register.' It gives clear context for usage, but does not explicitly mention alternatives or when NOT to use it, though the sibling names (abn_lookup, name_search) make the distinction obvious.

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