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

With no annotations provided, the description carries the full behavioral burden and does well by explicitly stating the return values (compliance score and missing fields), providing useful insight beyond the tool name. However, it does not disclose whether the operation is read-only or mention any validation side effects, so it is not fully transparent.

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 two short, targeted sentences: the first states the action and standard, the second states the output. There is no filler or repetition of schema/annotation content, making it maximally concise and well-structured.

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 tool with only two optional parameters and no output schema, the description provides enough context: the validation purpose, the legal framework, and the return shape. The parameter details are fully covered by the schema, and the sibling list shows a clear niche. It could be enhanced with a phrase about read-only behavior or input format preference, but it is largely sufficient.

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 input schema already provides complete descriptions for both parameters (pdf_path and pdf_base64) with 100% coverage, so the baseline is 3. The description adds no extra parameter semantics beyond what the schema already states, such as when to use one input format over the other.

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 ('Validate') tied to a resource ('invoice') and a precise legal standard (German §14 UStG), clearly differentiating it from sibling tools like invoice_extract and invoice_summary. It also states the key outputs (compliance score and missing mandatory fields), making the tool's purpose unambiguous.

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 should be used when legal compliance validation is needed, but it does not explicitly state when to use it over alternatives or mention exclusions. No alternative tools are referenced, leaving the agent to infer the use case from the word 'Validate'.

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