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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds the deterministic ordering ('newest first') and the raw endpoint, but says nothing about pagination behavior or rate limits. With annotations carrying the read-only signal, this is adequate but not rich.

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 short sentences with zero filler; the resource and scope come first and the endpoint detail trails it. Every clause 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?

For a simple read-only list with no output schema, the description covers what it returns, in what order, and the underlying endpoint, while the schema fully documents the three paging parameters. Missing only paging workflow detail, which is a minor gap.

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 after/limit/before are fully documented in the schema. The description adds no extra parameter meaning (no note that after/before are mutually exclusive or how to seed pagination), so the 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?

States a specific verb ('List') and resource ('letters') with the scope 'sent/scheduled' and the ordering 'newest first', plus the backing endpoint GET /v1/letters. It is clearly distinguishable from lob_get_letter, though it does not name sibling list tools such as lob_list_postcards.

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 scope phrase 'sent/scheduled letters' implies which letters are returned and implicitly excludes drafts, but there is no explicit when-to-use statement, no mention of when to prefer lob_get_letter, and no guidance on paging through results.

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