lob_list_lettersList sent/scheduled letters, newest first. Lob API: GET /v1/letters.
| Name | Required | Description | Default |
|---|---|---|---|
| after | No | Cursor for the next page (from a previous response's next_url). | |
| limit | No | Max results per page (1–100). Default 10. | |
| before | No | Cursor for the previous page (from a previous response's previous_url). |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true, so the description's mention of 'list' is consistent. The description adds the ordering behavior ('newest first') but does not disclose pagination details (e.g., use of cursors) or response structure beyond the API path.
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, zero waste. First sentence conveys purpose and ordering; second provides the API reference. Front-loaded and efficient.
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?
With no output schema, a description of return format (e.g., array of letter objects, pagination links) would be helpful. The tool is simple but misses contextual details about what the response contains, though the schema partially covers pagination.
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 the description does not need to explain parameters. It adds no new meaning beyond the schema, mentioning only the order (not a parameter). This meets the baseline for high coverage.
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?
Description clearly specifies the action (list), resource (letters), and ordering (newest first). It distinguishes from sibling tools like lob_list_postcards or lob_list_checks by naming the specific resource type.
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 description implies the tool is for retrieving a list of letters, but lacks explicit guidance on when to use it versus alternatives (e.g., get_letter for a single letter, or other list tools). No mention of prerequisites or contraindications.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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Every tool targets a distinct resource and action, with clear verb-noun names like create_address and verify_us_address. There is no overlapping functionality, and even similar operations (e.g., list for different resources) are distinct.
All tools share the 'lob_' prefix and follow a consistent verb_noun pattern (e.g., create_postcard, list_letters, verify_intl_address). Multi-word nouns use underscores, maintaining uniformity throughout.
With 18 tools, the set covers the primary mail fulfillment operations—address management, postcards, letters, checks, self-mailers, and address verification—without feeling bloated or sparse. The count is well-suited to the domain.
The tool set has notable gaps: no create_check or create_self_mailer, no cancel for letters or checks despite being referenced, no update/delete for addresses, and only list for templates. These missing operations will likely cause agent failures in common workflows.