attachPhoneNumber

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

Annotations already declare readOnlyHint=false, destructiveHint=false, and openWorldHint=false, so the safety profile is covered. The description adds only the word 'existing' as a prerequisite hint; it says nothing about whether the phone number must be unassigned, whether prior bindings are replaced, or what errors occur if the agent or number is missing.

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?

One short sentence, front-loaded with the verb and target, so it is efficient. The trailing '(Tags: Phone numbers)' artifact is metadata noise that earns no place in the description.

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 simple one-object mutation with fully documented parameters and no output schema, the description is minimally adequate. It leaves the return value and failure/prerequisite behavior unstated, which matters for a state-changing call that binds a purchased resource to an agent.

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% — agent_id and phone_number_id each carry their own schema descriptions — so the baseline of 3 applies. The description adds no format, ID-type, or constraint detail beyond what the schema already documents.

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 (attach) and resource (phone number) plus the target (an existing agent), so the action is unambiguous. It does not explicitly differentiate itself from the inverse sibling detachPhoneNumber, but the name and phrasing make the direction obvious without opening a 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?

There is no guidance on when to choose this over alternatives such as purchasePhoneNumber, importTwilioNumber, or detachPhoneNumber, and no stated prerequisites. The only usage signal is the implied 'attaching to an existing agent', which restates the purpose rather than routing the agent.

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