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

Goes well beyond the annotations: it discloses that nothing is sent or charged, that it produces a draft with the exact price, that the user's account is required, and that the sender can be in any country. It also describes the rendering output (A4, DIN 5008 blocks) and print-check behavior, which the safety annotations do not cover.

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?

Front-loaded with the when-to-use trigger and use cases, then the behavior and workflow. Dense and mostly waste-free, though the parenthetical layout list and formatting notes make it longer than strictly necessary.

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 14-parameter, nested-object tool with no output schema, it covers the essential workflow, cost transparency, auth requirement, and body formatting. It omits explanation of a few optional fields (envelope sizes, duplex, color), but these are minor for correct 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 coverage is 64%, so many fields (envelope, duplex, color, references, date, place) are documented by the schema. The description adds useful meaning for two things the schema does not: body mini-markup support (paragraphs, '- ' bullets, '1. ' lists, **bold**) and the purpose of registered mail. This is better than a bare baseline but does not fully compensate for the uncovered fields.

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?

States a specific verb and resource ('write a new paper letter from text') plus concrete use cases (cancel a contract, complaint, formal notice). The scoping phrase 'from text' and the explicit downstream step 'call send_letter' distinguish it from create_letter and send_letter among the siblings.

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?

Gives a clear when-to-use trigger with examples and embeds the follow-up workflow ('show the user the draft and the total, ask for confirmation, then call send_letter'). It does not explicitly name or exclude the closely named sibling create_letter, leaving the text-vs-other-source distinction to inference.

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