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

The annotation readOnlyHint is consistent with the description's claim of not saving the file. The description also specifies that it returns structured data, providing full transparency about the read-only behavior without any side effects.

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 a single, well-structured sentence that is concise and to the point. It avoids unnecessary details while covering the main functionality and output, making it easy for an agent to parse.

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?

Given the tool's moderate complexity (three optional parameters) and lack of an output schema, the description is complete. It lists the key return fields, which is essential for the agent to understand what data will be provided, and it clarifies the file type handling (XRechnung vs. ZUGFeRD-PDF).

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 provides 100% coverage with descriptive comments for each parameter, including the mutual exclusivity of xml and datei_base64. However, the tool description itself does not add further meaning to the parameters beyond what the schema already provides, so the baseline score of 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 clearly states the action (reads) and the resource (XRechnung or ZUGFeRD-PDF), and lists the specific data returned (sender, recipient, positions, amounts, due date, bank details). It distinguishes itself from sibling tools that create, check, or search invoices.

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 explains what the tool does but does not explicitly name alternative tools or conditions for choosing this one. It mentions 'ohne die Datei zu speichern' which hints at a read-only operation, but it lacks direct guidance on when to prefer this over rechnung_pruefen or rechnung_erstellen.

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