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

Annotations already declare readOnly, idempotent, non-destructive and open-world, so safety is covered structurally. The description adds real value beyond that by disclosing the return shape ('per-address deliverability + corrected components') and confirming the batch nature of the call.

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 purpose, then field requirements, then a worked example — three dense sentences with no filler. The inline example is functional rather than decorative, though it is slightly long.

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, the description steps in to describe the return payload (deliverability plus corrected components), and it enumerates required vs optional inputs. An agent has enough to call and interpret the tool; only batch limits and error behavior are unaddressed.

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 the schema already documents both parameters and the nested address fields. The description largely restates those field names and the required/optional split, adding only a concrete example, so it hovers at the baseline.

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 ('verify') and resource ('a list of US addresses in one request'), and the word 'list'/'bulk' implicitly distinguishes it from the singular lob_verify_address sibling. It stops short of naming the sibling to route between them, but the scope is unambiguous.

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?

Bulk vs. single-address usage is implied by 'in one request', but there is no explicit when-to-use guidance, no mention of which sibling (lob_verify_address, lob_autocomplete) to prefer, and no note on batch-size or rate limits. Usage is inferable rather than stated.

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