MailFixture

create_phone_number

Provision a dedicated US phone number for receiving SMS (paid plans only; numbers are receive-only — mailfixture never sends). Returns {id, phone_number, status}. If status is 'pending', call list_phone_numbers until it becomes 'active' before using the number in the flow under test; then call wait_for_sms_otp.

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "create_phone_number"
  }
}

Input Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

First observedJul 11, 2026

TDQS

A4.4/5.0

Behavior4/5

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

No annotations provided, so description carries full burden. It discloses that numbers are receive-only, returns {id, phone_number, status}, and explains pending status behavior. Transparent about limitations.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Two sentences, dense with information. The first sentence covers purpose and constraints; the second covers workflow. No wasted words.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

No output schema, but description specifies return format and related tools. Given zero parameters, it provides sufficient context for an agent to use correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Input schema has 0 parameters, so no parameter info needed. Baseline 4 for zero-param tools. Description does not add param info, but not required.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool provisions a dedicated US phone number for receiving SMS, with specific verb and resource. It distinguishes from siblings like list_phone_numbers and release_phone_number.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicitly mentions 'paid plans only' and 'receive-only', and provides conditional workflow: if status is 'pending', call list_phone_numbers then wait_for_sms_otp. Could be more explicit about when not to use, but adequate.

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

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