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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and closed-world behavior, so safety is covered. The description adds value annotations cannot: it enumerates the meaning of the `status` values (incomplete/ready/pending/action_required/verified/rejected/archived), explains that `missing` names outstanding customer inputs, and states the required `sms:read` scope — auth and result semantics go beyond structured fields.

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?

It is front-loaded with the purpose, then status semantics, then the workflow alternatives, and ends with a scope line — a logical order with no filler. The middle sentence is dense with product terms (10DLC, quotes) but each clause carries distinct information, so trimming would lose routing 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 an output schema present the description need not define return fields, yet it still explains what status/missing mean, and it supplies the permission scope and the create/update/register workflow. Nothing essential to calling a no-argument listing tool correctly is missing; only an explicit tie-breaker against similar read tools like sms_numbers_list or sms_list is absent.

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?

The tool takes zero parameters, so the baseline of 4 applies; the description correctly spends no space restating inputs. Instead it documents the shape of the returned status/missing values, which is more useful than parameter commentary would be here.

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 opens with a specific verb and resource ('List SMS brands') and immediately scopes the meaning of the result ('with setup status (whether SMS is ready)'). It also distinguishes this read operation from the sibling write tools sms_brands_create and sms_brands_update, so an agent can separate it from neighbors without opening the schema.

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?

It explains the surrounding workflow: creating/editing a brand is free via sms_brands_create / sms_brands_update, while carrier registration is a paid order priced by sms_quotes_create and placed with sms_quotes_confirm. That gives a clear sense of where this listing fits, though it never states an explicit 'use this when you need to check readiness before registering' trigger or any exclusion beyond the sibling mentions.

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