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

Annotations already declare destructiveHint=true, idempotentHint=false and readOnlyHint=false, so the risk profile is covered structurally. The description adds the business purpose but not what 'destructive' means here — e.g. whether an existing registration link on the number is replaced, whether unlinking is required first, or what happens if the registration is unapproved.

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?

A single well-formed sentence with the precondition and the payoff front-loaded; no filler, no restatement of the title.

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 two-parameter mutation with no output schema, the description covers intent and one precondition but omits failure behavior (unapproved registration, number already linked) and any hint at the success response. Adequate to call correctly in the happy path, incomplete for edge cases.

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 coverage is 50%: phone_number is documented in-schema, registration_id is not. The description partially compensates by raising the approval requirement for the registration, but adds nothing about phone_number beyond what the schema says and nothing about identifier format for registration_id.

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?

Specific verb (attach) plus specific resources (a number, an approved 10DLC registration) and a stated outcome (it can send that registration's traffic). An agent knows exactly what the operation accomplishes, though it doesn't distinguish itself from the nearby assign_number_to_customer sibling.

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 phrase "approved 10DLC registration" implies a precondition for use, which is genuinely useful. However, there is no explicit when-to-use / when-not guidance and no reference to alternatives such as assign_number_to_customer or update_number_pool, so routing among the number-management siblings is left to inference.

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