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

Annotations already state readOnly/idempotent/non-destructive/closed-world, so the description's added value is the ordering guarantee ('newest first'), the returned field set, and the semantics of has_unseen_updates as an unread-events marker. It stops short of saying whether reading the list itself clears that flag, which is the one behavioral question an agent might still have.

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 usage trigger, then the payload, then cross-references; nearly every sentence carries signal. The greeting-card and batch asides are terse but slightly clipped in phrasing ('batches sums up each batch'), which costs a bit of polish rather than length.

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 single-filter list tool with an output schema, the description covers trigger, ordering, field inventory, and sibling routing. Remaining gaps are minor: no pagination/truncation guidance and no note on whether the read affects has_unseen_updates.

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?

Only one parameter (limit), and the schema already documents it at 100% coverage including default and maximum. The description adds nothing about paging or what happens when the limit truncates a large letter history, so baseline 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?

Specific verb (list/returns) plus resource (letters of the user), with an explicit trigger context ('user asks about earlier letters by post or Einschreiben'). It also distinguishes itself from the sibling that reads details: 'Call get_letter_status for its events.'

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 concrete when-to-use example ('which letters went out last month') and routes the agent to get_letter_status for event timelines, so the split between list and detail tools is explicit. It also clarifies that greeting cards appear in results, preventing a wrong assumption about the dataset.

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