Generating Custom Field

## When to Use This Skill

Use this skill when you need to:
- Create custom fields on any object
- Generate field metadata for any field type
- Set up relationship fields (Lookup or Master-Detail)
- Create formula or roll-up summary fields
- Troubleshoot deployment errors related to custom fields

# Salesforce Custom Field Generator and Validator

## Overview

Generate and validate Salesforce Custom Field metadata with mandatory constraints to prevent deployment errors. This skill has special focus on the **highest-failure-rate field types**: Roll-up Summary and Master-Detail relationships.

## Specification

## 1. Purpose

This document defines the mandatory constraints for generating CustomField metadata XML. The agent must verify these constraints before outputting XML to prevent Metadata API deployment errors.

**Critical Focus Areas:**
- Roll-up Summary field format errors
- Master-Detail field attribute restrictions
- Lookup Filter restrictions

---

## 2. Universal Mandatory Attributes

Every generated field must include these tags:

| Attribute | Requirement | Notes |
|-----------|-------------|-------|
| `<fullName>` | Required | Derive from `<label>`: capitalize each word, replace spaces with `_`, append `__c`. Must start with a letter. E.g., label `Total Contract Value` → `Total_Contract_Value__c` |
| `<label>` | Required | The UI name (Title Case) |
| `<description>` | Mandatory | State the business "why" behind the field |
| `<inlineHelpText>` | Mandatory | Provide actionable guidance for the end-user. Must add value beyond the label (e.g., "Enter the value in USD including tax" instead of just "The amount") |

### External ID Configuration

**Trigger:** If the user mentions "integration," "importing data," "external system ID," or "unique key from [System Name]," set `<externalId>true</externalId>`.

**Applicable Types:** Text, Number, Email

---

## 3. Technical Interplay: Precision, Scale, and Length

To ensure deployment success, follow these mathematical constraints:

### Precision vs. Scale Rules

- `precision` is the total digits; `scale` is the decimal digits
- **Rule:** `precision ≤ 18` AND `scale ≤ precision`
- **Calculation:** Digits to the left of decimal = `precision - scale`

### The "Fixed 255" Rule

For standard TextArea types, the Metadata API requires `<length>255</length>`, even though it isn't configurable in the UI.

### Visible Lines

Mandatory for Long/Rich text and Multi-select picklists to control UI height.

---

## 4. Field Data Types

### 4.1 Simple Attribute Types

| Type | `<type>` Value | Required Attributes |
|------|----------------|---------------------|
| Auto Number | `AutoNumber` | `displayFormat` (must include `{0}`), `startingNumber` |
| Checkbox | `Checkbox` | Default `defaultValue` to `false` |
| Date | `Date` | No precision/length required |
| Date/Time | `DateTime` | No precision/length required |
| Email | `Email` | Built-in format validation |
| Lookup Relationship | `Lookup` | `referenceTo`, `relationshipName`, `deleteConstraint` |
| Master-Detail Relationship | `MasterDetail` | `referenceTo`, `relationshipName`, `relationshipOrder` |
| Number | `Number` | `precision`, `scale` |
| Currency | `Currency` | Default precision: 18, scale: 2 |
| Percent | `Percent` | Default precision: 5, scale: 2 |
| Phone | `Phone` | Standardizes phone number formatting |
| Picklist | `Picklist` | `va