CallMCP — Phone Call MCP Server

Get Invoice Email Recipients

get_billing_contacts

Read-onlyIdempotent

Read who gets the monthly invoice email for a business. Every paid invoice is always emailed to the business owner (returned masked); up to 3 extra addresses, such as a bookkeeper or office inbox, get the same email.

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": "get_billing_contacts"
  }
}

Input Schema

Name	Required	Description	Default
`business_id`	No	Business ID (optional only when the token can access exactly one business).

Output Schema

Name	Required	Description
`error`	No	Present when success is false
`success`	Yes	Whether the tool completed successfully
`business_id`	No
`owner_email`	No	The owner's login email, masked. The owner always gets every invoice.
`extra_emails`	No
`max_extra_emails`	No
`monthly_invoice_email`	No

Schema Changelog

Changes observed during successful MCP inspections.

First observedNov 12, 2026

TDQS

A4.2/5.0

Behavior4/5

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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and closed-world scope, so safety is covered. The description adds genuinely non-obvious behavioral context: the owner is always a recipient and is returned masked, and there are at most 3 additional addresses that receive the same email. That explains the shape and limits of the result beyond the annotations.

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, zero padding. The purpose is front-loaded and the second sentence supplies only the non-obvious recipient-composition rule.

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

Completeness5/5

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

This is a simple, single-parameter read tool with full annotation coverage and a declared output schema, so return values need not be spelled out. The description still adds the one thing the schema cannot convey: that the owner is always included (masked) alongside up to 3 extra addresses. Complete for the tool's complexity.

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

Parameters5/5

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

There is a single optional parameter, business_id, and the schema already documents both its meaning and the condition under which it may be omitted (token access to exactly one business). The description adds nothing new about the parameter, but with 100% coverage and one optional parameter, the schema fully carries this burden.

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

Purpose4/5

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

The description opens with a specific verb and resource: read the recipients of the monthly invoice email for a business. It is immediately distinguishable from the write-side sibling by the 'Read' verb, but it never names set_billing_contacts or any other sibling explicitly, so differentiation is inferred rather than stated.

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

Usage Guidelines3/5

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

Usage is implied by 'Read' versus the set_* siblings, and the sentence is clearly about inspection rather than modification. There is no explicit statement of when to prefer this tool over alternatives, no prerequisites, and no note about what to do if you actually need to change recipients.

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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