Attach a phone number to an agent using an agent ID and number ID, enabling that agent to handle calls and SMS on the number.
Attach a phone number to an agent so the agent handles calls/SMS on that number. Takes an agent ID and a phone number ID.
| Name | Required | Description | Default |
|---|---|---|---|
| agent_id | Yes | The agent ID | |
| number_id | Yes | The phone number ID to attach |
Changes observed during successful MCP inspections.
v0.7.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations only declare idempotentHint, so the description carries most of the burden. It usefully explains the observable consequence of attaching (the agent starts handling calls/SMS on that number), but omits permissions, conflict/replacement behavior, and failure modes.
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, purpose and effect front-loaded with no filler. The second sentence is largely redundant with the required-parameter list in the schema, a minor waste.
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 two-parameter tool with full schema coverage and no output schema, the core purpose is covered. However, nothing is said about where to obtain a valid number_id, whether the number must be purchased first, or what happens if the number is already attached.
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%, so both parameters are already documented in the schema; the description merely restates 'takes an agent ID and a phone number ID' without adding format, source-of-ID, or constraint details. Baseline 3 applies.
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 to an agent) plus the concrete effect: the agent then handles calls/SMS on that number. The contrast with the sibling detach_number is implied by the verb, but the description never names alternatives or differentiates explicitly.
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?
No guidance on when to attach vs. when not to, no prerequisites (e.g. the number must already exist in the account, whether an existing attachment is replaced), and no mention of the sibling detach_number or list_numbers for discovering number IDs.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.