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

Beyond the annotations (readOnlyHint=false, openWorldHint=true, destructiveHint=false), the description adds two operationally important facts an agent would otherwise not know: the cost is debited from the prepaid balance, and the letter is irreversible once dispatched. It stops short of covering the test-key behavior, idempotency expectations, or what happens on insufficient balance.

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?

One compact sentence with the core action front-loaded and the cost/irreversibility caveats immediately after. No filler, though the very short text leaves obvious room for routing and parameter hints that would earn their 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 is incomplete relative to a nine-parameter financial, irreversible mutation with no output schema and no annotation coverage of cost or reversibility. It says nothing about return values, success/failure shape, or the address and file parameters, so an agent could not confidently construct a correct call from it.

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 only 56% and the description adds nothing about any of the nine parameters — no mention of letterType (almindelig vs rekommanderet), the sender/recipient address objects, text vs fileBase64 exclusivity, or the role of idempotencyKey. The description does not compensate for the undocumented half of the schema.

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 opens with a concrete verb and resource: "Sender et fysisk brev i Danmark" (send a physical letter in Denmark). It is clear what the tool does, but it never names or contrasts with the closest sibling, create_letter_order, so the agent must infer the distinction from names alone.

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?

There is no explicit when-to-use or when-not-to-use guidance, and no mention of alternatives such as create_letter_order (order-based flow) or get_pricing/get_balance. The prepaid-balance and non-cancellable statements describe consequences of calling, not conditions for choosing this tool.

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