check_imessage_capabilityVerify if phone numbers support iMessage or fall back to SMS. Check up to 100 E.164 numbers at once to determine delivery method.
Check whether phone numbers can receive iMessage vs SMS. Accepts up to 100 numbers.
| Name | Required | Description | Default |
|---|---|---|---|
| phones | Yes | Phone numbers in E.164 format. |
Changes observed during successful MCP inspections.
v0.1.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries the burden. It accurately states the core behavior and the input limit, but it does not disclose the return format, per-number result shape, or behavior for invalid/non-E.164 numbers. Basic operation is clear, but deep behavior is not.
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 with the purpose front-loaded. The second sentence about accepting up to 100 numbers duplicates the schema's maxItems, so it doesn't fully earn its place, but there is no unnecessary fluff.
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?
The input side is well covered by the schema, and the tool is simple. However, with no output schema, the description should specify what the tool returns or how to interpret the capability result; it currently leaves that to inference.
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 the baseline is 3. The description only restates the maxItems constraint already present in the schema and adds no new meaning about E.164 validation, deduplication, or error handling.
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 operation ('check whether phone numbers can receive iMessage vs SMS') on a concrete resource (phone numbers). The iMessage-vs-SMS distinction differentiates it clearly from send_imessage, get_message_status, and list_conversations.
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 use case is implied: check capability before sending an iMessage. However, the description never explicitly says when to use this tool versus send_imessage or get_message_status, nor does it mention any prerequisites or exclusions.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.