lob_us_zip_lookupReturn the cities and state associated with a US ZIP code. Non-mutating. Lob API: POST /v1/us_zip_lookups.
| Name | Required | Description | Default |
|---|---|---|---|
| zip_code | Yes | A 5-digit US ZIP code, e.g. '94107'. |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true, and the description reinforces with 'Non-mutating'. No additional behavioral traits (e.g., error handling, rate limits) are disclosed beyond the annotation.
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 efficient sentences front-load the purpose, omit extraneous details, and include API reference. Every sentence adds value.
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 one parameter, read-only annotation, and no output schema, the description is mostly complete. Minor gap: does not explicitly state that multiple cities may be returned for one ZIP code, but overall adequate.
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 covers 100% of parameter info, and the description adds no new meaning beyond the schema's '5-digit US ZIP code' example. Baseline 3 is appropriate.
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 clearly states the tool returns 'cities and state associated with a US ZIP code', uses a specific verb 'look up', and distinguishes from siblings like verification or autocomplete tools via the 'Non-mutating' tag and API endpoint.
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?
No guidance on when to use this tool versus siblings such as lob_us_autocomplete or lob_verify_us_address. The 'Non-mutating' hint is implicit but does not provide explicit context for selection.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Add one secure layer between your agents and this server.
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.