build_mls_message

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

No annotations are provided, so the description carries the full behavioral burden. It discloses two useful behavioral traits: the output is base64-encoded and the response is document-level rather than per-line. However, it does not mention side effects, error behavior, validation, or whether the operation is purely in-memory. The core behavior is reasonably covered, but not exhaustively.

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 with no wasted words. The primary purpose is front-loaded, and the alternative use case is stated compactly. Every part of the description earns its place.

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 complexity (11 parameters, output schema present), the description provides the essential context: what it builds, the output encoding, and the crucial document-level vs per-line distinction. It does not explicitly state whether the tool is side-effect-free or whether it validates inputs, but the schema and output schema cover most remaining details. A small gap remains, but overall it is complete enough for correct selection and invocation.

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%, so the input schema already fully documents all 11 parameters. The description adds no parameter-specific meaning, which is acceptable given that the schema does the heavy lifting. 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 clearly states the tool's action and resource: 'Build a document-level MLS response and return it base64-encoded.' The second sentence further sharpens the purpose by excluding per-line responses, which distinguishes this tool from the alternative construction path. This is specific and 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 explicitly tells the agent when NOT to use this tool: 'For per-line responses, build the document directly with mcp_einvoicing_core.peppol.mls.build_mls.' This provides a clear condition and an explicit alternative, leaving no ambiguity about tool selection.

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