billy-mcp

create_contact_person

Add a contact person with name or email to an existing Billy contact for invoice emailing.

Instructions

Add a contact person (name and/or email) to an existing Billy contact. Emails are used to mail invoices.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "contactId": "<contactId>"
    },
    "name": "create_contact_person"
  }
}

Input Schema

Name	Required	Description
`name`	No	Person name (name or email must be set)
`email`	No	Email address (name or email must be set)
`verbose`	No	Return the full Billy response. Default false: compact records with key fields only (saves ~90% context)
`contactId`	Yes	Parent contact ID
`isPrimary`	No	Mark as the primary contact person

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.3.0Jul 8, 2026

TDQS

A4.1/5.0

Behavior3/5

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

Annotations indicate it is not read-only and not destructive, which aligns with 'Add'. The description adds the email usage context but does not disclose other behaviors like success/failure handling or constraints. With annotations covering basic safety, this is adequate but not exceptional.

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 concise sentences: first defines the action, second provides a practical reason for the email parameter. No unnecessary words, front-loaded with essential information.

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

Completeness3/5

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

No output schema is provided, and the description does not mention return values. The verbose parameter hints at response structure, but missing information on what the tool returns (e.g., created person ID). Adequate for basic use, but could be more complete for a mutation tool.

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?

Schema coverage is 100%, so parameters are already described. The description adds value by explaining the email purpose ('Emails are used to mail invoices') and noting that name or email must be set. This goes beyond the schema descriptions, earning a higher score.

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 action ('Add'), the target ('existing Billy contact'), and the data ('name and/or email'). It also provides context ('Emails are used to mail invoices'), distinguishing it from creating a new contact or listing contact persons.

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?

The description implicitly indicates use on existing contacts ('to an existing Billy contact'), providing context for when to use. It does not explicitly list alternatives or when not to use, but the context is clear. The sibling tools help differentiate.

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