Platform Custom Field Generate

Salesforce Custom Field Generator and Validator

Overview

Generates and validates Salesforce CustomField metadata XML, with special handling for the highest-failure-rate types — Roll-Up Summary and Master-Detail. The agent must verify the constraints below before outputting XML to prevent Metadata API deployment errors.

1. Universal Mandatory Attributes

Every generated field must include these tags:

<description> and <inlineHelpText> are mandatory outputs even though the Metadata API does not enforce them — omitting them produces low-quality metadata.

File path (SFDX source format): save each field as force-app/main/default/objects/<Object>/fields/<FieldName>__c.field-meta.xml, where <Object> is the object's API name (Account, Opportunity, or a custom Inventory_Item__c). A correct XML at the wrong path is never seen by the Metadata API.

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

2. Precision, Scale, and Length Rules

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

TextArea: do NOT include <length> — the Metadata API fixes the length at 255 implicitly and rejects an explicit <length> value with "Can not specify 'length' for a CustomField of type TextArea". Omit <length> entirely; the field only needs <fullName>, <label>, and <type>TextArea</type>.

Visible Lines

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

3. Field Data Types

3.1 Simple Attribute Types

3.2 Computed & Multi-Value Types

3.3 Specialized Types

Picklist restricted default

Always set <restricted>true</restricted> inside <valueSet> unless the user explicitly says the picklist should accept custom values not in the admin-defined list (e.g. "unrestricted"/"open"). Restricted sets are capped at 1,000 total values (active + inactive). Minimal inline shape:

<valueSet>
  <restricted>true</restricted>
  <valueSetDefinition>
    <sorted>false</sorted>
    <value><fullName>Option_A</fullName><default>false</default><label>Option A</label></value>
  </valueSetDefinition>
</valueSet>

3.4 Advanced Picklists

The inline <valueSetDefinition> above is the simple case. Full rules and worked correct/incorrect examples for everything below are in references/advanced-picklists.md — load it for any non-trivial picklist. Section numbers in parentheses below (e.g. "ref §1") point to that reference file, not to this skill. The hard rules:

• Value-set reference (ref §1). A <valueSet> holds EITHER <valueSetName> (reference) OR <valueSetDefinition> (inline) — never both. Reference by the bare developer name — Standard set Industry, GlobalValueSet Priority_Levels with NO __gvs and no __c (the __gvs suffix is org-storage display only; the Metadata API uses the bare name). A value-set-backed field is <restricted>true</restricted>. Creating the value set is the platform-value-set-generate skill's job; this one only references it.
• Value-name fidelity (ref §3). A picklist value's <fullName>/<label> keep the user's exact text including spaces (Closed Won, never Closed_Won). The space→_ + __c rule is for the FIELD name only.
• Dependent picklists (ref §2). Use the modern API 38.0+ form: <controllingField> + one <valueSettings> (<controllingFieldValue>+<valueName>) per pair; never the legacy <picklist>/<picklistValues>/<controllingFieldValues> tags. Both controlling and dependent fields MUST be <restricted>true</restricted>, even if the request doesn't say so.
• Enhanced value attributes (ref §3). <value> entries also accept <color> (hex, leading #), <isActive> (false retires a value), and a value-level <description>.
• Scoping a picklist to a record type (ref §5). Per-record-type value visibility lives on the RecordType (<picklistValues>), not the field. The RecordType file carries its own <fullName> (bare developer name). First decide if the object needs a BusinessProcess: only Opportunity / Lead / Case / Solution require one — they won't deploy without a <businessProcess> (Required field is missing: businessProcess), even when only a custom picklist is filtered. There you emit two coupled files: the businessProcesses/<Name>.businessProcess-meta.xml file AND a matching <businessProcess><Name></businessProcess> inside the <RecordType> (after <active>, before <picklistValues>; the <fullName> in the BP file is bare, never object-qualified). Custom objects (*__c) and all other standard objects (Account, Contact, …) need NO BusinessProcess — emit the RecordType alone; do not invent one. Scope limit: picklist-value visibility per record type only — NOT general record-type authoring (compact layouts, page layouts, branding).

4. Master-Detail Relationship Rules CRITICAL

Master-Detail fields have strict attribute restrictions that differ from Lookup fields. Violating these rules causes deployment failures.

Forbidden Attributes on Master-Detail Fields

NEVER include these attributes on Master-Detail fields:

Master-Detail vs Lookup Comparison

INCORRECT — Master-Detail with forbidden attributes:

<CustomField xmlns="http://soap.sforce.com/2006/04/metadata">
  <fullName>Account__c</fullName>
  <type>MasterDetail</type>
  <referenceTo>Account</referenceTo>
  <relationshipName>Contacts</relationshipName>
  <relationshipOrder>0</relationshipOrder>
  <required>true</required>                     <!-- WRONG: remove -->
  <deleteConstraint>Cascade</deleteConstraint>  <!-- WRONG: remove -->
  <lookupFilter>...</lookupFilter>              <!-- WRONG: remove entire block -->
</CustomField>

Errors: Master-Detail Relationship Fields Cannot be Optional or Required · Can not specify 'deleteConstraint' for a CustomField of type MasterDetail · Lookup filters are only supported on Lookup Relationship Fields

CORRECT — Master-Detail field:

<CustomField xmlns="http://soap.sforce.com/2006/04/metadata">
  <fullName>Account__c</fullName>
  <label>Account</label>
  <description>Links this record to its parent Account</description>
  <type>MasterDetail</type>
  <referenceTo>Account</referenceTo>
  <relationshipLabel>Child Records</relationshipLabel>
  <relationshipName>ChildRecords</relationshipName>
  <relationshipOrder>0</relationshipOrder>
  <reparentableMasterDetail>false</reparentableMasterDetail>
  <writeRequiresMasterRead>false</writeRequiresMasterRead>
  <!-- NO required, deleteConstraint, or lookupFilter -->
</CustomField>

CORRECT — Lookup field (with optional attributes):

<CustomField xmlns="http://soap.sforce.com/2006/04/metadata">
  <fullName>Related_Account__c</fullName>
  <label>Related Account</label>
  <description>Optional link to a related Account</description>
  <type>Lookup</type>
  <referenceTo>Account</referenceTo>
  <relationshipLabel>Related Records</relationshipLabel>
  <relationshipName>RelatedRecords</relationshipName>
  <required>false</required>
  <deleteConstraint>SetNull</deleteConstraint>
  <lookupFilter>
    <active>true</active>
    <filterItems>
      <field>Account.Type</field>
      <operation>equals</operation>
      <value>Customer</value>
    </filterItems>
    <isOptional>false</isOptional>
  </lookupFilter>
</CustomField>

Additional Master-Detail Rules

• Relationship Order: First Master-Detail on object = 0, second = 1
• Relationship Name: Must be a plural PascalCase string (e.g., Travel_Bookings)
• Junction Objects: Use two Master-Detail fields for standard many-to-many (enables Roll-ups)
• Limit: Maximum 2 Master-Detail relationships per object. Use Lookup for additional relationships.

5. Roll-Up Summary Field Rules CRITICAL

Roll-up Summary fields have the highest deployment failure rate. Follow these rules exactly.

Required Elements for Roll-Up Summary

Forbidden Elements on Roll-Up Summary

NEVER include these attributes on Roll-Up Summary fields:

Format Rules for summaryForeignKey and summarizedField

CRITICAL: Both summaryForeignKey and summarizedField MUST use the fully qualified format:

ChildObjectAPIName__c.FieldAPIName__c

Decision Logic:

• summaryForeignKey = ChildObject__c.MasterDetailFieldOnChild__c
• summarizedField = ChildObject__c.FieldToSummarize__c

INCORRECT — Roll-Up Summary with common errors:

<CustomField xmlns="http://soap.sforce.com/2006/04/metadata">
  <fullName>Total_Amount__c</fullName>
  <label>Total Amount</label>
  <type>Summary</type>
  <precision>18</precision>           <!-- WRONG: Remove - inherited from source -->
  <scale>2</scale>                    <!-- WRONG: Remove - inherited from source -->
  <summaryOperation>sum</summaryOperation>
  <summaryForeignKey>Order__c</summaryForeignKey>        <!-- WRONG: Missing field name -->
  <summarizedField>Amount__c</summarizedField>           <!-- WRONG: Missing object name -->
</CustomField>

Errors:

• Can not specify 'precision' for a CustomField of type Summary
• Must specify the name in the CustomObject.CustomField format (e.g. Account.MyNewCustomField)

CORRECT — Roll-Up Summary (SUM operation):

<CustomField xmlns="http://soap.sforce.com/2006/04/metadata">
  <fullName>Total_Amount__c</fullName>
  <label>Total Amount</label>
  <description>Sum of all line item amounts</description>
  <inlineHelpText>Automatically calculated from child line items</inlineHelpText>
  <type>Summary</type>
  <summaryOperation>sum</summaryOperation>
  <summarizedField>Order_Line_Item__c.Amount__c</summarizedField>
  <summaryForeignKey>Order_Line_Item__c.Order__c</summaryForeignKey>
  <!-- NO precision, scale, required, or length -->
</CustomField>

COUNT: identical structure to SUM but omit <summarizedField> entirely (and keep <summaryForeignKey>). MIN / MAX: identical to SUM — just <summaryOperation>min</summaryOperation> or max, with <summarizedField> pointing at the field to find the minimum/maximum of. The Quick Reference table below covers all four.

Roll-Up Summary Quick Reference

Roll-Up Summary Prerequisites

• Roll-Up Summary fields can ONLY be created on the parent object in a Master-Detail relationship
• The child object MUST have a Master-Detail field pointing to this parent
• The summarized field must exist on the child object

6. Formula Field Rules

Formula Result Types

A Formula is not a type itself. The <formula> tag is added to a field whose <type> is set to the result data type:

• Checkbox, Currency, Date, DateTime, Number, Percent, Text

Formula XML Generation Rules

• The contents of the <formula> tag MUST be wrapped in a <![CDATA[ ... ]]> section. This prevents the XML parser from interpreting formula operators (like &, <, >) as XML markup.
• If the formula text itself contains the literal sequence ]]>, escape it by breaking the CDATA block: e.g., <![CDATA[Text_Field__c & "]]]]><![CDATA[>"]]>
• NEVER use an attribute or tag named returnType. This does not exist in the Metadata API. The <type> tag defines the return data type of the formula result.

formulaTreatBlanksAs Rule

Decision Logic:

• IF formula result type = Number, Currency, or Percent → set <formulaTreatBlanksAs>BlankAsZero</formulaTreatBlanksAs>
• IF formula result type = Text, Date, or DateTime → set <formulaTreatBlanksAs>BlankAsBlank</formulaTreatBlanksAs>

INCORRECT — Using Formula as type:

<CustomField xmlns="http://soap.sforce.com/2006/04/metadata">
  <fullName>Calculated_Value__c</fullName>
  <type>Formula</type>  <!-- WRONG: Formula is not a valid type -->
  <returnType>Number</returnType>  <!-- WRONG: returnType does not exist in Metadata API -->
  <formula>Field1__c + Field2__c</formula>  <!-- WRONG: Missing CDATA wrapper -->
</CustomField>

CORRECT — Formula field:

<CustomField xmlns="http://soap.sforce.com/2006/04/metadata">
  <fullName>Calculated_Value__c</fullName>
  <label>Calculated Value</label>
  <description>Sum of Field1 and Field2</description>
  <type>Number</type>  <!-- Result type, not "Formula" -->
  <precision>18</precision>
  <scale>2</scale>
  <formula><![CDATA[Field1__c + Field2__c]]></formula>
  <formulaTreatBlanksAs>BlankAsZero</formulaTreatBlanksAs>
</CustomField>

Formula Field Dependencies & Functions

• Formula fields that reference other fields fail deployment if the referenced field doesn't exist or hasn't deployed yet — deploy referenced fields first.
• Use ISPICKVAL() (not ==) for picklist comparisons.
• For the full formula-function reference (TEXT/VALUE/CASE/DAY/MONTH/DATEVALUE/ISCHANGED type rules), defer to the platform-validation-rule-generate skill, which owns formula-function correctness.

7. Common Deployment Errors

8. Verification Checklist

Before generating CustomField XML, verify:

Universal Checks

• Does <fullName> use valid format and end in __c?
• Are <description> and <inlineHelpText> both populated and meaningful?
• Is <label> in Title Case?
• Are there no XML comments (<!-- ... -->) before the root <CustomField> element? (Comments before the root element break SDR's parser)

Master-Detail Field Checks CRITICAL

• Is <required> attribute ABSENT? (Master-Detail is always required)
• Is <deleteConstraint> attribute ABSENT? (Master-Detail always cascades)
• Is <lookupFilter> block ABSENT? (Only for Lookup fields)
• Is <relationshipOrder> set to 0 or 1?
• Is parent object's <sharingModel> set to ControlledByParent?

Lookup Field Checks

• Is <deleteConstraint> set to SetNull, Restrict, or Cascade?
• Is <relationshipName> in plural PascalCase?

Picklist Field Checks

• Does each <valueSet> contain EITHER <valueSetName> OR <valueSetDefinition> — never both?
• For a value-set reference: is <restricted>true</restricted> set?
• For a StandardValueSet reference: is the name the bare enum with NO __c (e.g. Industry)?
• For a GlobalValueSet reference: is the name the bare developer name with NO __gvs suffix?
• For dependent picklists: is <controllingField> set, with one <valueSettings> (<controllingFieldValue> + <valueName>) per pair?
• For dependent picklists: is the deprecated <picklist>/<picklistValues>/<controllingFieldValues> form ABSENT?
• Are all picklist value <fullName> values unique, start with a letter, and free of hyphens? (spaces are allowed — do NOT replace them with underscores, per the §3.4 value-name fidelity rule)

Roll-Up Summary Field Checks CRITICAL

• Is <precision> attribute ABSENT?
• Is <scale> attribute ABSENT?
• Is <summaryForeignKey> in format ChildObject__c.MasterDetailField__c?
• For SUM/MIN/MAX: Is <summarizedField> in format ChildObject__c.FieldName__c?
• For COUNT: Is <summarizedField> ABSENT?
• Does the child object have a Master-Detail field to this parent?

Formula Field Checks

• Is <type> set to result type (NOT "Formula")?
• Is <formula> content wrapped in <![CDATA[ ... ]]>?
• Is <returnType> attribute ABSENT? (does not exist in Metadata API)
• Is <formulaTreatBlanksAs> set to BlankAsZero for numeric results or BlankAsBlank for text/date results?
• Do all referenced fields exist and deploy before this field?

Numeric Field Checks

• Is scale ≤ precision?
• Is precision ≤ 18?

Text Area Checks

• For TextArea: Is <length> omitted? (The API rejects an explicit <length> value on TextArea fields.)
• For LongTextArea/Html: Is <visibleLines> set?

Relationship Limit Checks

• Are there 2 or fewer Master-Detail relationships on the object?
• Are there 15 or fewer Lookup relationships on the object?

Naming Checks

• Is the API name free of reserved words (Order, Group, Select, etc.)?
• Is the API name unique on this object?