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 burden of behavioral disclosure. It does state that the result is base64-encoded, which is an important characteristic. However, it does not mention validation behavior, error handling, or whether the operation has any side effects, leaving some important traits unspecified for a tool with zero annotation hints.

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 sentences with no filler. The core action and output format are front-loaded, and the alternative is given in the second sentence. Every word 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?

The description explains the tool's purpose, output encoding, and the key distinction from per-line building, while the output schema covers return details and the input schema covers parameters. It does not elaborate on the 'document-level' concept further, but for a builder with complete schemas, the provided context 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?

Schema description coverage is 100%, so every parameter is already documented in the input schema. The description does not add additional parameter-level meaning, which is acceptable and matches the baseline of 3.

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 ('Build') with a clearly defined resource ('document-level MLS response') and specifies the return format ('base64-encoded'). It also distinguishes this tool from per-line response building, removing ambiguity about its scope.

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 second sentence explicitly tells the agent when *not* to use this tool: for per-line responses, it should build the document directly with `mcp_einvoicing_core.peppol.mls.build_mls`. This is clear, actionable, and directly addresses the key alternative.

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