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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false, and openWorldHint=false, so the safety profile is fully covered. The description adds only that status is returned; it says nothing about pagination, result volume, or whether pending/draft registrations are included.

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 short sentences, front-loaded with the core purpose and no filler. The trailing clause 'an approved one' is slightly elliptical — it relies on the reader resolving 'one' to 'registration' — but the overall length is well matched to a zero-parameter list tool.

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?

For a no-param, read-only list tool with no output schema and full annotation coverage, the description supplies enough to call it correctly and understand why it matters. The remaining gap is result shape (does it include submission status history?), which is minor at this complexity.

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 no parameters, so there is no parameter semantics to document and the baseline of 4 applies. The description does not claim any filtering or pagination inputs, which is consistent with the empty schema.

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 concrete verb and resource: lists 10DLC brand and campaign registrations plus their approval status. It does not differentiate itself from nearby siblings such as get_registration, list_registration_submissions, or list_toll_free_verifications, so the agent must infer the scope difference.

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 second sentence ('Marketing from a local number needs an approved one') implies the motivation — check approval status before sending — but never states an explicit when-to-use rule or names an alternative tool. Usage is inferable rather than directed.

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