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

Annotations supply only destructiveHint=true, so the description carries most of the burden and does it well: it discloses the non-sending behavior, the return identifier format, and the underlying endpoint. It does not address whether the record is validated/verified, whether creation is idempotent, or what errors arise, which keeps it from a 5.

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?

Three compact sentences, front-loaded with the purpose and the key negative constraint, then the return value, then the API route. Nothing is redundant or padded.

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 correctly compensates by explaining the returned adr_ identifier and its downstream use. It is nearly complete for a 9-parameter creation tool, though it omits validation behavior and failure modes.

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 78%, so the schema already documents name, address_line1, state, country default, etc. The description adds no parameter-level syntax, defaults, or format rules beyond that, so the 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?

States a specific verb and resource ('Create a reusable saved address record') and immediately scopes it against the obvious misreading with '(does NOT send any mail)'. Names the concrete artifact it produces (adr_… id) and the API route, so it is cleanly distinguishable from lob_create_letter/postcard.

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?

Gives clear forward-looking usage ('usable as `to`/`from` in mail tools') and an explicit exclusion ('does NOT send any mail'), which routes the agent away from the mail-sending siblings. It stops short of naming alternatives like lob_verify_us_address for agents who only need validation rather than persistence.

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