platform-custom-field-generate

name	platform-custom-field-generate
description	Use this skill when users need to create, generate, or validate Salesforce Custom Field metadata. Trigger when users mention custom fields, field types, Roll-up Summary fields, Master-Detail relationships, Lookup relationships, formula fields, picklists, dependent (controlling) picklists, referencing a value set from a field, or scoping/limiting picklist values for a specific record type. Also use when users encounter field deployment errors, especially around Roll-up Summary format, Master-Detail constraints, formula issues, or a record type that won't deploy without a business process. Use this skill for custom field metadata work, field generation, and field troubleshooting. DO NOT TRIGGER for creating or customizing the value set itself — defining a new GlobalValueSet, or modifying a StandardValueSet catalog like Industry or Lead Source — use platform-value-set-generate instead; this skill covers the field that references a value set, not the value set definition.
metadata	{"version":"1.0","minApiVersion":"60.0","relatedSkills":["platform-validation-rule-generate","platform-value-set-generate"],"mcpTools":{"metadata-grounding":{"tools":["search_metadata"],"semver":">=1.0.0"}}}

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.

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1. Universal Mandatory Attributes

Every generated field must include these tags:

Attribute	Requirement	Notes
<fullName>	Required	Field name only: 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. This rule is for the FIELD name. Picklist VALUE <fullName> is different — keep it exactly as the user spelled it, spaces and all, no __c (e.g. Closed Won, NOT Closed_Won). See references/advanced-picklists.md (ref §3).
<label>	Required	The UI name (Title Case)
<description>	Always include	Explain the business reason why this field exists.
<inlineHelpText>	Always include	Actionable end-user guidance that adds value beyond the label (e.g., "Enter the value in USD including tax", not "The amount").

<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

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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.

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3. Field Data Types

3.1 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	valueSet containing EITHER valueSetDefinition (inline) OR valueSetName (reference); restricted (see "Picklist restricted default" below; advanced cases in §3.4)
Text	Text	length (Max 255)
Text Area	TextArea	None — do NOT include <length>; the API fixes length at 255 implicitly

3.2 Computed & Multi-Value Types

Type	<type> Value	Required Attributes
Formula	Result type (e.g., Number)	formula, formulaTreatBlanksAs
Roll-Up Summary	Summary	See Section 5 for complete requirements
Multi-Select Picklist	MultiselectPicklist	valueSet, visibleLines (default 4)

3.3 Specialized Types

Type	<type> Value	Required Attributes
Geolocation	Location	scale, displayLocationInDecimal

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 : the file AND a matching inside the (after , before ; the in the BP file is , never object-qualified). picklist-value visibility per record type only — NOT general record-type authoring (compact layouts, page layouts, branding).

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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:

Forbidden Attribute	Why	What Happens
<required>	Master-Detail is ALWAYS required by design	Deployment error
<deleteConstraint>	Master-Detail ALWAYS cascades deletes	Deployment error
<lookupFilter>	Only supported on Lookup fields	Deployment error

Master-Detail vs Lookup Comparison

Attribute	Master-Detail	Lookup
<required>	FORBIDDEN	Optional
<deleteConstraint>	FORBIDDEN (always CASCADE)	Required (SetNull, Restrict, Cascade)
<lookupFilter>	FORBIDDEN	Optional
<relationshipOrder>	Required (0 or 1)	Not applicable
<reparentableMasterDetail>	Optional	Not applicable
<writeRequiresMasterRead>	Optional	Not applicable

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</>
    
    false
  

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.

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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

Element	Requirement	Format
<type>	Required	Always Summary
<summaryOperation>	Required	count, sum, min, or max
<summaryForeignKey>	Required	ChildObject__c.MasterDetailField__c
<summarizedField>	Conditional	Required for sum, min, max. NOT for count

Forbidden Elements on Roll-Up Summary

NEVER include these attributes on Roll-Up Summary fields:

Forbidden Attribute	Why
<precision>	Summary inherits from summarized field
<scale>	Summary inherits from summarized field
<required>	Not applicable to Summary fields
<length>	Not applicable to 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

Operation	summarizedField Required?	Use Case
count	NO	Count number of child records
sum	YES	Add up numeric values
min	YES	Find smallest value
max	YES	Find largest value

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

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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.

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7. Common Deployment Errors

Error Message	Cause	Fix
ConversionError: Invalid XML tags or unable to find matching parent xml file for CustomField	XML comments placed before the root <CustomField> element	Remove XML comments (<!-- ... -->) that appear before <CustomField> in the .field-meta.xml file
Field [FieldName] does not exist. Check spelling.	Referenced field does not exist or has not been deployed yet	Verify the referenced field exists and is deployed before this field
DUPLICATE_DEVELOPER_NAME	Field fullName already exists on the object	Use a unique business-driven name
MAX_RELATIONSHIPS_EXCEEDED	More than 2 Master-Detail or 15 Lookup fields on the object	Use Lookup for 3rd+ Master-Detail; review Lookup count
Reserved keyword error	Using Order__c, Group__c, etc.	Rename to Status_Order__c, etc.
Value set must reference a value set name or define a value set, but not both	<valueSet> has both <valueSetName> and <valueSetDefinition>	Keep exactly one (see Section 3.4)
duplicate value found: [X] is defined multiple times	Two <value> entries share a <fullName>	Make every picklist value <fullName> unique
Invalid fullName on a picklist value	Value <fullName> starts with a digit or contains hyphens	Start with a letter; no hyphens, no leading digit. Spaces ARE allowed — do NOT underscore them (see §3.4 value-name fidelity)
Element ...picklist is not allowed	Deprecated ≤37.0 dependent-picklist syntax (<picklist>/<picklistValues>/<controllingFieldValues>)	Use the modern valueSettings/controllingFieldValue/valueName form (Section 3.4)

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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?