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

The annotations already establish read-only, idempotent, non-destructive, closed-world behavior, so the description only has to add operational context — and it does: newest-first ordering, fixed page sizing, cursor/has_more pagination mechanics, and an explicit statement that letter content is never returned. It does not state rate limits or what an empty list looks like, but the important behavioral traits are covered.

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, both front-loaded with the resource scope first and the pagination contract second. Nothing is repeated from the schema verbatim and no sentence is disposable.

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?

No output schema exists, so the description carries the burden of describing results — and it enumerates the returned fields (orderId, status, service, sheets, chargeCzk, createdAt, orderCode, tracking), notes the absent field, and explains the pagination sentinels. For a two-parameter, read-only list tool this is sufficient to call it correctly.

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 100%, so both parameters are already documented structurally. The description still adds real meaning by tying the opaque next_cursor value to the cursor argument and explaining that has_more is false on the final page, which is the semantics the schema does not spell out.

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 specific verb and resource plus scope: 'List the letters sent from the signed-in account, newest first, one page at a time.' That is far more precise than the title alone. It does not name the siblings get_letter_status or send_letter_cz, but the list-vs-status-vs-send distinction is legible enough that an agent can route correctly.

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?

Usage is implied by the scoping phrase 'sent from the signed-in account' and by the pagination loop instruction ('Pass next_cursor back as cursor for the next page'). There is no explicit when-not guidance and no mention of when an agent should prefer get_letter_status for a single order's state instead of listing.

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