afv-library/skills/generating-custom-lightning-type/SKILL.md

name	description	metadata
generating-custom-lightning-type	Use this skill when users need to create Custom Lightning Types (CLTs) for Einstein Agent actions or structured input/output schemas. Trigger when users mention CLT, Custom Lightning Types, custom lightning type with widget renderer, custom lightning type with widget, CLT with widget renderer, CLT with widget, JSON schemas for agents, type definitions, lightning__objectType, or editor/renderer configurations. When a widget renderer is requested, you MUST first read the widget-rendition.md reference file in this skill's references/ directory and follow its complete workflow. This is complex - always use this skill for CLT work.	version 1.0

When to Use This Skill

Use this skill when you need to:

• Create Custom Lightning Types (CLTs) for structured inputs/outputs
• Generate JSON Schema-based type definitions for Lightning Platform
• Configure CLTs for Einstein Agent actions
• Set up editor and renderer configurations for custom UI
• Create CLTs with widget/mosaic/fragment rendition
• Troubleshoot deployment errors related to Custom Lightning Types

Specification

CustomLightningType Metadata Specification

Overview & Purpose

Custom Lightning Types (CLTs) are JSON Schema-based type definitions used by the Lightning Platform (including Einstein Agent actions) to describe structured inputs/outputs and drive editor/renderer experiences.

Configuration

• Choose referenced CLT pattern for nested objects - When you need a reusable or separately deployed nested type, create a CLT for that shape and reference it with "lightning:type": "c__<CLTName>". That string is the referenced type’s lightning:type value / FQN / registered identifier — not the JSON Schema title.
• Choose standard Lightning types when the structure is simple and can be expressed with properties and supported primitive lightning:type identifiers.
• Choose Apex class types (@apexClassType/...) when the structure already exists server-side and you want the Apex class to define the shape.
• Include editor/renderer config only when you need custom UI behavior (custom LWC input/output components). Otherwise, omit.
• Widget rendition: After schema.json is drafted, you must read references/widget-rendition.md and follow the "Widget renderer pattern" section below for complete guidance. Do NOT attempt widget generation without reading the reference file first.

Critical Rules (Read First)

• Root object schemas MUST include:
  • "type": "object"
  • "title"
  • "lightning:type": "lightning__objectType"
  • "unevaluatedProperties": false
• "unevaluatedProperties" is enforced as false by the CLT metaschema. Do not set it to true.
• Root object schemas MUST NOT include "examples" when "unevaluatedProperties": false is set.
• Nested objects (inside properties) MUST NOT set "lightning:type": "lightning__objectType".
  • Nested objects can be: references to other CLTs using c__<CLTName> syntax.
• List/array properties are highly restricted by the CLT metaschema:
  • CRITICAL LIMITATION: the CLT metaschema may reject the items keyword entirely. Treat items as disallowed by default.
  • Root-level arrays (direct children of the root properties):
    • MUST include "lightning:type": "lightning__listType"
    • MUST NOT include "items"
    • OPTIONAL "type": "array"
  • Nested arrays (arrays inside nested objects) are the most common failure:
    • MUST include "type": "array"
    • MUST NOT include "lightning:type": "lightning__listType"
    • MUST NOT include "items"
• When "unevaluatedProperties": false is set, any unknown keyword will fail validation. Prefer removing keywords over relaxing strictness.
• Apex class CLTs are minimal:
  • Include only title, description (optional), and lightning:type set to @apexClassType/....
  • Do not add type, properties, required, or unevaluatedProperties.

Additional CLT Metaschema Validations

• Org namespace validation: titles/descriptions and other string fields may be validated to ensure you are not using an org namespace in places that are disallowed.
• Lightning type validation: CLTs are validated to prevent referencing internal namespaces (for example, disallowing types from internal namespaces like sfdc_cms where not permitted).
• Object type validation: the CLT root is validated to ensure lightning:type is exactly lightning__objectType.

Primitive Types & Constraints

• lightning__textType
  • Max length 255
• lightning__multilineTextType
  • Max length 2000
• lightning__richTextType
  • Max length 100000
• lightning__urlType
  • Max length 2000
  • Optional lightning:allowedUrlSchemes enum values: https, http, relative, mailto, tel
• lightning__dateType
  • Data pattern: YYYY-MM-DD
• lightning__timeType
  • Data pattern: HH:MM:SS.sssZ
• lightning__dateTimeType
  • Data shape is an object with required dateTime and optional timeZone
• lightning__numberType
  • Decimal numbers; optional maximum, minimum, multipleOf
• lightning__integerType
  • Whole numbers only; optional maximum, minimum
• lightning__booleanType
  • true/false

Allowed Property-Level Keywords

When strict validation is enabled (unevaluatedProperties: false), keep each property minimal and prefer only keywords known to be allowed:

• title, description, einstein:description
• type (when used, ensure it matches the chosen lightning:type)
• lightning:type
• maximum, minimum, multipleOf (numeric)
• maxLength, minLength (string)
• const, enum
• lightning:textIndexed, lightning:supportsPersonalization, lightning:localizable
• lightning:uiOptions, lightning:allowedUrlSchemes
• lightning:tags (metaschema restricts values; currently flow is the only known allowed tag)

Generation Workflow

⚠️ Widget renderer requested? STOP before step 1. If the user requested a "widget renderer", "mosaic", "widget", or "fragment": you MUST read references/widget-rendition.md NOW before doing anything else — before drafting schema, before creating any files, before planning steps. The API context examples show c/<componentName> renderers — those are the custom LWC pattern, NOT the widget pattern. Do not follow them for widget rendition.

1. Confirm the CLT approach
   • If referencing Apex: capture the exact class reference (@apexClassType/namespace__ClassName$InnerClass).
   • If using standard primitives: list the fields, their Lightning primitive types, and which fields are required.
2. Draft schema.json
   • Start with the root object structure (required root fields).
   • Add properties using valid primitive lightning:type identifiers.
   • For nested-object properties, use CLT Reference pattern:
     • "lightning:type": "c__<CLTName>" to reference another CLT
     • The referenced CLT must be deployed to the org before the parent CLT.
   • For Apex-based nested objects: Use @apexClassType/... when structure exists server-side.
   • If the prompt explicitly requires true nested object output, prefer an Apex-based CLT (@apexClassType/...) for deploy-safe nested structures.
   • For arrays: follow the strict list rules (avoid items; avoid lightning:type on nested arrays).
   • Before deployment, verify exact lightning:type spellings (for example, use lightning__richTextType, not misspelled variants).
3. (Optional) Draft editor.json (only if custom UI is required)
   • Supported shape: Top-level editor object with editor.componentOverrides and editor.layout.
     • Top-level editor object.
     • Use editor.componentOverrides for component overrides.
     • Use editor.layout for layout.
     • DEPRECATED: Do NOT use propertyRenderers or view — these are legacy keys. Always use componentOverrides and layout instead.
   • Root override pattern (most common for fully custom editing UI):
     • editor.componentOverrides["$"] = { "definition": "c/<yourEditorComponent>", "attributes": { ... } }
     • When passing schema data into a custom LWC, use attribute mapping with the {!$attrs.<name>} syntax: e.g. "attributes": { "myField": "{!$attrs.value}" } so the runtime binds schema values to your component's attributes.
     • CRITICAL: The <name> in {!$attrs.<name>} must be a property defined in your type schema. For example, if your schema has a property called temperature, use {!$attrs.temperature}, not {!$attrs.value} unless value is an actual property.
   • Property-level override pattern (for individual fields):
     • editor.componentOverrides["<propertyName>"] = { "definition": "es_property_editors/<...>" }
     • Valid editor components (examples): es_property_editors/inputText, es_property_editors/inputNumber, es_property_editors/inputRichText, es_property_editors/inputImage, es_property_editors/inputTextarea. Do not use es_property_editors/inputList.
   • Collection editor (for root-level lightning__listType properties): Use a collection-level override so the list is edited by a custom component: collection.editor.componentOverrides["$"] = { "definition": "c/<yourCollectionEditorComponent>" }. Alternatively, use editor.layout with lightning/propertyLayout and attributes.property = "<listPropertyName>" for default list editing.
   • Layout pattern:
     • editor.layout.definition = "lightning/verticalLayout"
     • editor.layout.children[*].definition = "lightning/propertyLayout" with attributes.property = "<propertyName>"
     • CRITICAL: lightning/propertyLayout only accepts the property attribute. Do NOT add label, title, or any other attributes — these will fail validation with additionalProperties: false errors.
   • Avoid known-invalid patterns:
     • Do not use es_property_editors/inputList.
     • Do not use itemSchema attributes.
4. (Optional) Draft renderer.json (only if custom UI or mosaic rendition is required)
   • ⚠️ DECIDE FIRST — widget or custom LWC? Before writing any renderer code or planning any steps:
     • If the user requested "widget", "mosaic", "fragment", or "cross-platform rendering": you MUST use the Widget renderer pattern below. Do NOT create a custom LWC. Do NOT use the root override pattern with c/<componentName>. Skip directly to the Widget renderer pattern now.
     • Otherwise: use the root override pattern or property-level overrides described below.
   • Supported shape: Top-level renderer object with renderer.componentOverrides and renderer.layout.
     • Top-level renderer object.
     • Use renderer.componentOverrides for component overrides.
     • Use renderer.layout for layout.
     • DEPRECATED: Do NOT use propertyRenderers or view — these are legacy keys. Always use componentOverrides and layout instead.
   • Widget renderer pattern (for widget rendition — use when user requests "widget", "mosaic", "fragment", or "cross-platform rendering"):
     • Structure: renderer.componentOverrides["$"] = { "type": "mosaic", "definition": "tile/mosaic", "children": [ /* UEM tree of blocks and regions */ ] }
     • CRITICAL: Do NOT create a custom LWC component (e.g. c/<componentName>) for widget rendering. Widget rendition uses a tile/mosaic UEM block tree — not a custom component. Creating a custom LWC here is always wrong.
     • REQUIRED workflow:
       • STOP: Do NOT attempt to build the UEM tree yourself.
       • MANDATORY FIRST STEP: You MUST fetch the reference file references/widget-rendition.md located in this skill's directory before proceeding.
       • Follow the complete workflow documented in widget-rendition.md using the generated CLT schema as the grounding schema.
       • The widget-rendition.md reference contains the full widget generation workflow: discovering UEM blocks via discoverUiComponents, calling getUiComponentSchemas, building the UEM tree, and writing renderer.json.
       • Do not attempt to generate widget rendition without first fetching the widget-rendition.md reference file.
   • Root override pattern (for custom LWC rendering — only when widget/mosaic was NOT requested):
     • renderer.componentOverrides["$"] = { "definition": "c/<yourRendererComponent>", "attributes": { ... } }
     • Use {!$attrs.<name>} in attribute mappings when binding schema data to custom renderer component attributes.
     • CRITICAL: Attribute mappings like {!$attrs.propertyName} must reference properties that actually exist in your type schema. Referencing non-existent properties will fail validation.
     • Type matching: Attribute values must match the expected type for the component. For example, if a component expects a string attribute, passing an integer will fail validation.
   • Property-level override pattern:
     • renderer.componentOverrides["<propertyName>"] = { "definition": "es_property_editors/outputText" | "es_property_editors/outputNumber" | "es_property_editors/outputImage" | ... }. Valid renderer components (examples): es_property_editors/outputText, es_property_editors/outputNumber, es_property_editors/outputImage. Avoid input-style components in the renderer.
   • Layout pattern for renderer:
     • renderer.layout.definition = "lightning/verticalLayout"
     • renderer.layout.children[*].definition = "lightning/propertyLayout" with attributes.property = "<propertyName>"
     • CRITICAL: Same as editor layouts, lightning/propertyLayout only accepts the property attribute. Do NOT add label, title, or any other attributes.
   • Collection renderer (for root-level lightning__listType properties): Use collection.renderer.componentOverrides["$"] = { "definition": "c/<yourListRendererComponent>" } or es_property_editors/genericListTypeRenderer to render the list.
5. Place files in the correct bundle structure
   • lightningTypes/<TypeName>/schema.json
   • (Optional) lightningTypes/<TypeName>/lightningDesktopGenAi/editor.json
   • (Optional) lightningTypes/<TypeName>/lightningDesktopGenAi/renderer.json
   • For Gen AI / Copilot the standard path is lightningDesktopGenAi/. Other targets (e.g. Experience Builder, Mobile Copilot, Enhanced Web Chat) use different subfolders when supported: experienceBuilder/, lightningMobileGenAi/, enhancedWebChat/.
6. Configure custom LWC components (if using custom components)
   • CRITICAL: Custom LWC components referenced in editor/renderer configs MUST have the correct target configuration in their -meta.xml files:
     • For editor components (c/<componentName> used in editor.json): The LWC's -meta.xml file must include <target>lightning__AgentforceInput</target>
     • For renderer components (c/<componentName> used in renderer.json): The LWC's -meta.xml file must include <target>lightning__AgentforceOutput</target>
   • Without the correct target, deployment will fail with: Invalid target configuration. To use 'c/componentName' as a renderer/editor, your js-meta.xml file must include valid target 'lightning__AgentforceOutput/Input'.
   • Example -meta.xml for a renderer component:

     <?xml version="1.0" encoding="UTF-8"?>
     <LightningComponentBundle xmlns="http://soap.sforce.com/2006/04/metadata">
         <apiVersion>60.0</apiVersion>
         <isExposed>true</isExposed>
         <targets>
             <target>lightning__AgentforceOutput</target>
         </targets>
     </LightningComponentBundle>
     

7. Deploy and validate
   • Run a final schema sanity check before deploy: valid lightning:type names, required fields present, and no disallowed keywords.
   • Deploy the bundle using your org's standard metadata deployment flow (e.g. Salesforce CLI or IDE). The MCP client or tooling in use should provide or integrate with the appropriate deploy/retrieve commands for Lightning Type bundles.
   • Validate incrementally: if deployment fails, remove disallowed keywords first (especially examples, items, nested lightning:type).

Common Deployment Errors

Error / Symptom	Likely Cause	Fix
Schema validation fails due to unknown keyword	unevaluatedProperties: false + disallowed keyword (commonly examples, items)	Remove the offending keyword; keep schema minimal
Nested object validation failure	Org/channel validation rejects nested object typing in LightningTypeBundle	Use CLT reference (c__<CLTName>) or Apex class types
Invalid CLT reference	Referenced CLT doesn't exist in org or incorrect syntax	Deploy the referenced CLT first; c__<CLTName> must match the referenced type’s lightning:type value / FQN / registered identifier, not title
Invalid or misspelled lightning:type (for example, lightning__richtextType instead of lightning__richTextType)	Incorrect generated type name	Cross-check all lightning:type values against supported type names and correct them before deployment
Array property rejected	Use of items (or lightning:type in nested arrays) rejected by validator	For nested arrays: keep only type: "array". For root arrays: use minimal structure; remove items if rejected
Apex-based CLT rejected	Extra fields added (e.g., type, properties)	Use only title, optional description, and lightning:type
Editor config rejected	Use of invalid patterns (es_property_editors/inputList, itemSchema) or unrecognized top-level keys	Use editor.componentOverrides and editor.layout; keep config minimal
additionalProperties error on layout attributes	Adding label or other attributes to lightning/propertyLayout	Only use property attribute in lightning/propertyLayout. Remove label, title, or any other attributes
Invalid target configuration for custom LWC	Custom LWC component's -meta.xml missing required target (lightning__AgentforceInput or lightning__AgentforceOutput)	Add correct target to LWC's -meta.xml: use lightning__AgentforceInput for editors, lightning__AgentforceOutput for renderers
Attribute mapping doesn't exist in type schema	Using {!$attrs.propertyName} where propertyName is not defined in schema	Ensure all attribute mappings reference actual properties in your type schema's properties section
additionalProperties error with deprecated keys	Using propertyRenderers or view in editor/renderer config	Replace deprecated propertyRenderers with componentOverrides and view with layout
Type mismatch in component attributes	Passing wrong type for component attribute (e.g., integer instead of string)	Ensure attribute values match the expected type defined by the component

Verification Checklist

• Root schema has type: "object", title, lightning:type: "lightning__objectType", and unevaluatedProperties: false
• Root schema does not include examples when strict validation is enabled
• No nested object includes lightning:type: "lightning__objectType"
• Arrays are defined minimally (especially nested arrays)
• Only supported primitive lightning:type identifiers are used for leaf properties
• Apex class CLTs contain only title/description and lightning:type: "@apexClassType/..."
• Bundle structure and filenames match Lightning Types requirements
• Editor config uses only allowed patterns (no es_property_editors/inputList, no itemSchema); use valid components (e.g. es_property_editors/inputText, es_property_editors/inputNumber) or custom c/ components
• Renderer config uses output-style components (e.g. es_property_editors/outputText, es_property_editors/outputNumber) where applicable, not input editors
• Widget renderer uses tile/mosaic UEM block tree (NOT a custom c/<componentName> LWC)
• Layout configurations use lightning/propertyLayout with ONLY the property attribute (no label, title, or other attributes)
• All attribute mappings ({!$attrs.propertyName}) reference properties that exist in the type schema
• Custom LWC components have correct targets in -meta.xml: lightning__AgentforceInput for editors, lightning__AgentforceOutput for renderers