diff --git a/packages/apidom-ls/src/config/codes.ts b/packages/apidom-ls/src/config/codes.ts
index 0ce246d7c3..1e39e60355 100644
--- a/packages/apidom-ls/src/config/codes.ts
+++ b/packages/apidom-ls/src/config/codes.ts
@@ -841,6 +841,7 @@ enum ApilintCodes {
 
   OPENAPI2_REFERENCE = 3240000,
   OPENAPI2_REFERENCE_FIELD_$REF_FORMAT_URI = 3240100,
+  OPENAPI2_REFERENCE_NOT_USED = 3240300,
 
   OPENAPI3_0 = 5000000,
 
@@ -1066,6 +1067,11 @@ enum ApilintCodes {
   OPENAPI3_0_REFERENCE = 5260000,
   OPENAPI3_0_REFERENCE_FIELD_$REF_FORMAT_URI = 5260100,
   OPENAPI3_0_REFERENCE_FIELD_$REF_NO_SIBLINGS,
+  OPENAPI3_0_REFERENCE_FIELD_$REF_REQUEST_BODIES = 5260200,
+  OPENAPI3_0_REFERENCE_FIELD_$REF_REQUEST_BODIES_NAMING,
+  OPENAPI3_0_REFERENCE_FIELD_$REF_REQUEST_BODIES_NAMING_SCHEMA,
+  OPENAPI3_0_REFERENCE_FIELD_$REF_HEADER = 5260300,
+  OPENAPI3_0_REFERENCE_FIELD_$REF_PARAMETER = 5260400,
 
   OPENAPI3_0_LINK = 5270000,
   OPENAPI3_0_LINK_FIELD_OPERATION_REF_FORMAT_URI = 5270100,
diff --git a/packages/apidom-ls/src/config/common/schema/lint/$ref--not-used.ts b/packages/apidom-ls/src/config/common/schema/lint/$ref--not-used.ts
new file mode 100644
index 0000000000..a810e98391
--- /dev/null
+++ b/packages/apidom-ls/src/config/common/schema/lint/$ref--not-used.ts
@@ -0,0 +1,19 @@
+import { DiagnosticSeverity } from 'vscode-languageserver-types';
+
+import ApilintCodes from '../../../codes.ts';
+import { LinterMeta } from '../../../../apidom-language-types.ts';
+import { OpenAPI2, OpenAPI3, OpenAPI31 } from '../../../openapi/target-specs.ts';
+
+const $refNotUsedLint: LinterMeta = {
+  code: ApilintCodes.OPENAPI2_REFERENCE_NOT_USED,
+  source: 'apilint',
+  message: 'Definition was declared but never used in document',
+  severity: DiagnosticSeverity.Warning,
+  linterFunction: 'apilintReferenceNotUsed',
+  linterParams: ['string'],
+  marker: 'key',
+  data: {},
+  targetSpecs: [...OpenAPI2, ...OpenAPI3, ...OpenAPI31],
+};
+
+export default $refNotUsedLint;
diff --git a/packages/apidom-ls/src/config/common/schema/lint/$ref-3-0--request-bodies.ts b/packages/apidom-ls/src/config/common/schema/lint/$ref-3-0--request-bodies.ts
new file mode 100644
index 0000000000..165b28a11c
--- /dev/null
+++ b/packages/apidom-ls/src/config/common/schema/lint/$ref-3-0--request-bodies.ts
@@ -0,0 +1,28 @@
+import { DiagnosticSeverity } from 'vscode-languageserver-types';
+
+import ApilintCodes from '../../../codes.ts';
+import { LinterMeta } from '../../../../apidom-language-types.ts';
+import { OpenAPI3 } from '../../../openapi/target-specs.ts';
+
+const $ref3RequestBodiesLint: LinterMeta = {
+  code: ApilintCodes.OPENAPI3_0_REFERENCE_FIELD_$REF_REQUEST_BODIES,
+  source: 'apilint',
+  message:
+    'requestBody schema $refs must point to a position where a Schema Object can be legally placed',
+  severity: DiagnosticSeverity.Error,
+  linterFunction: 'parentExistFields',
+  linterParams: [['requestBody']],
+  conditions: [
+    {
+      targets: [{ path: '$ref' }],
+      function: 'apilintValueRegex',
+      params: ['^(?!.*#/components/schemas).*$'],
+    },
+  ],
+  marker: 'value',
+  target: '$ref',
+  data: {},
+  targetSpecs: OpenAPI3,
+};
+
+export default $ref3RequestBodiesLint;
diff --git a/packages/apidom-ls/src/config/common/schema/lint/index.ts b/packages/apidom-ls/src/config/common/schema/lint/index.ts
index 76426b5749..b8ab3f4a64 100644
--- a/packages/apidom-ls/src/config/common/schema/lint/index.ts
+++ b/packages/apidom-ls/src/config/common/schema/lint/index.ts
@@ -3,6 +3,7 @@ import allowedFieldsOpenAPI3_0Lint from './allowed-fields-openapi-3-0.ts';
 import $idFormatURILint from './$id--format-uri.ts';
 import $refValidLint from './$ref--valid.ts';
 import $refNoSiblingsLint from './$ref--no-siblings.ts';
+import $ref3RequestBodiesLint from './$ref-3-0--request-bodies.ts';
 import additionalItemsNonArrayLint from './additional-items--non-array.ts';
 import additionalItemsTypeLint from './additional-items--type.ts';
 import additionalItemsTypeOpenAPI3_1__AsyncAPI2Lint from './additional-items--type-openapi-3-1--asyncapi-2.ts';
@@ -81,6 +82,7 @@ import uniqueItemsNonArrayLint from './unique-items--non-array.ts';
 import uniqueItemsTypeLint from './unique-items--type.ts';
 import writeOnlyTypeLint from './write-only--type.ts';
 import exampleDeprecatedLint from './example--deprecated.ts';
+import $refNotUsedLint from './$ref--not-used.ts';
 
 const schemaLints = [
   allowedFieldsOpenAPI2_0Lint,
@@ -88,6 +90,8 @@ const schemaLints = [
   $idFormatURILint,
   $refValidLint,
   $refNoSiblingsLint,
+  $refNotUsedLint,
+  $ref3RequestBodiesLint,
   additionalItemsNonArrayLint,
   additionalItemsTypeLint,
   additionalItemsTypeOpenAPI3_1__AsyncAPI2Lint,
diff --git a/packages/apidom-ls/src/config/openapi/header/lint/$ref-3-0--header.ts b/packages/apidom-ls/src/config/openapi/header/lint/$ref-3-0--header.ts
new file mode 100644
index 0000000000..fec5d97d49
--- /dev/null
+++ b/packages/apidom-ls/src/config/openapi/header/lint/$ref-3-0--header.ts
@@ -0,0 +1,27 @@
+import { DiagnosticSeverity } from 'vscode-languageserver-types';
+
+import ApilintCodes from '../../../codes.ts';
+import { LinterMeta } from '../../../../apidom-language-types.ts';
+import { OpenAPI3 } from '../../target-specs.ts';
+
+const $ref3HeaderNamingLint: LinterMeta = {
+  code: ApilintCodes.OPENAPI3_0_REFERENCE_FIELD_$REF_HEADER,
+  source: 'apilint',
+  message: 'OAS3 header $Ref should point to Header Object',
+  severity: DiagnosticSeverity.Error,
+  linterFunction: 'parentExistFields',
+  linterParams: [['header']],
+  conditions: [
+    {
+      targets: [{ path: '$ref' }],
+      function: 'apilintValueRegex',
+      params: ['^(?!.*#/components/headers).*$'],
+    },
+  ],
+  marker: 'value',
+  target: '$ref',
+  data: {},
+  targetSpecs: OpenAPI3,
+};
+
+export default $ref3HeaderNamingLint;
diff --git a/packages/apidom-ls/src/config/openapi/header/lint/index.ts b/packages/apidom-ls/src/config/openapi/header/lint/index.ts
index c4ebe7ccfa..fc56c3ae47 100644
--- a/packages/apidom-ls/src/config/openapi/header/lint/index.ts
+++ b/packages/apidom-ls/src/config/openapi/header/lint/index.ts
@@ -35,8 +35,10 @@ import minItemsTypeLint from './min-items--type.ts';
 import uniqueItemsTypeLint from './unique-items--type.ts';
 import enumTypeLint from './enum--type.ts';
 import multipleOfTypeLint from './multiple-of--type.ts';
+import $ref3HeaderNamingLint from './$ref-3-0--header.ts';
 
 const lints = [
+  $ref3HeaderNamingLint,
   descriptionTypeLint,
   requiredTypeLint,
   deprecatedTypeLint,
diff --git a/packages/apidom-ls/src/config/openapi/parameter/lint/$ref-3-0--parameter.ts b/packages/apidom-ls/src/config/openapi/parameter/lint/$ref-3-0--parameter.ts
new file mode 100644
index 0000000000..3e3ec0f43a
--- /dev/null
+++ b/packages/apidom-ls/src/config/openapi/parameter/lint/$ref-3-0--parameter.ts
@@ -0,0 +1,27 @@
+import { DiagnosticSeverity } from 'vscode-languageserver-types';
+
+import ApilintCodes from '../../../codes.ts';
+import { LinterMeta } from '../../../../apidom-language-types.ts';
+import { OpenAPI3 } from '../../target-specs.ts';
+
+const $ref3ParameterNamingLint: LinterMeta = {
+  code: ApilintCodes.OPENAPI3_0_REFERENCE_FIELD_$REF_PARAMETER,
+  source: 'apilint',
+  message: 'OAS3 parameter $Ref should point to Parameter Object',
+  severity: DiagnosticSeverity.Error,
+  linterFunction: 'apilintValueRegex',
+  linterParams: ['^(.*#/components/parameters).*$'],
+  marker: 'value',
+  target: '$ref',
+  conditions: [
+    {
+      targets: [{ path: '$ref' }],
+      function: 'parentExistFields',
+      params: [['paths']],
+    },
+  ],
+  data: {},
+  targetSpecs: OpenAPI3,
+};
+
+export default $ref3ParameterNamingLint;
diff --git a/packages/apidom-ls/src/config/openapi/parameter/lint/index.ts b/packages/apidom-ls/src/config/openapi/parameter/lint/index.ts
index 6e2bfd1f76..690566dcb4 100644
--- a/packages/apidom-ls/src/config/openapi/parameter/lint/index.ts
+++ b/packages/apidom-ls/src/config/openapi/parameter/lint/index.ts
@@ -42,8 +42,10 @@ import uniqueItemsTypeLint from './unique-items--type.ts';
 import enumTypeLint from './enum--type.ts';
 import multipleOfTypeLint from './multiple-of--type.ts';
 import inPathTemplateLint from './in-path-template.ts';
+import $ref3ParameterNamingLint from './$ref-3-0--parameter.ts';
 
 const lints = [
+  $ref3ParameterNamingLint,
   nameTypeLint,
   nameRequiredLint,
   inEquals2_0Lint,
diff --git a/packages/apidom-ls/src/config/openapi/request-body/lint/$ref-3-0--request-bodies-naming-schema.ts b/packages/apidom-ls/src/config/openapi/request-body/lint/$ref-3-0--request-bodies-naming-schema.ts
new file mode 100644
index 0000000000..934bdece81
--- /dev/null
+++ b/packages/apidom-ls/src/config/openapi/request-body/lint/$ref-3-0--request-bodies-naming-schema.ts
@@ -0,0 +1,28 @@
+import { DiagnosticSeverity } from 'vscode-languageserver-types';
+
+import ApilintCodes from '../../../codes.ts';
+import { LinterMeta } from '../../../../apidom-language-types.ts';
+import { OpenAPI3 } from '../../target-specs.ts';
+
+const $ref3RequestBodiesNamingSchemaLint: LinterMeta = {
+  code: ApilintCodes.OPENAPI3_0_REFERENCE_FIELD_$REF_REQUEST_BODIES_NAMING_SCHEMA,
+  source: 'apilint',
+  message:
+    "requestBody $refs cannot point to '#/components/schemas/…', they must point to '#/components/requestBodies/…'",
+  severity: DiagnosticSeverity.Error,
+  linterFunction: 'parentExistFields',
+  linterParams: [['requestBodies']],
+  conditions: [
+    {
+      targets: [{ path: '$ref' }],
+      function: 'apilintValueRegex',
+      params: ['^(.*#/components/schemas).*$'],
+    },
+  ],
+  marker: 'value',
+  target: '$ref',
+  data: {},
+  targetSpecs: OpenAPI3,
+};
+
+export default $ref3RequestBodiesNamingSchemaLint;
diff --git a/packages/apidom-ls/src/config/openapi/request-body/lint/$ref-3-0--request-bodies-naming.ts b/packages/apidom-ls/src/config/openapi/request-body/lint/$ref-3-0--request-bodies-naming.ts
new file mode 100644
index 0000000000..204db6868b
--- /dev/null
+++ b/packages/apidom-ls/src/config/openapi/request-body/lint/$ref-3-0--request-bodies-naming.ts
@@ -0,0 +1,27 @@
+import { DiagnosticSeverity } from 'vscode-languageserver-types';
+
+import ApilintCodes from '../../../codes.ts';
+import { LinterMeta } from '../../../../apidom-language-types.ts';
+import { OpenAPI3 } from '../../target-specs.ts';
+
+const $ref3RequestBodiesNamingLint: LinterMeta = {
+  code: ApilintCodes.OPENAPI3_0_REFERENCE_FIELD_$REF_REQUEST_BODIES_NAMING,
+  source: 'apilint',
+  message: 'requestBody $refs must point to a position where a requestBody can be legally placed',
+  severity: DiagnosticSeverity.Error,
+  linterFunction: 'parentExistFields',
+  linterParams: [['requestBodies']],
+  conditions: [
+    {
+      targets: [{ path: '$ref' }],
+      function: 'apilintValueRegex',
+      params: ['^(?!.*#/components/(requestBodies|schemas)).*$'],
+    },
+  ],
+  marker: 'value',
+  target: '$ref',
+  data: {},
+  targetSpecs: OpenAPI3,
+};
+
+export default $ref3RequestBodiesNamingLint;
diff --git a/packages/apidom-ls/src/config/openapi/request-body/lint/index.ts b/packages/apidom-ls/src/config/openapi/request-body/lint/index.ts
index 8f74dd5336..0fadc4cbca 100644
--- a/packages/apidom-ls/src/config/openapi/request-body/lint/index.ts
+++ b/packages/apidom-ls/src/config/openapi/request-body/lint/index.ts
@@ -4,8 +4,12 @@ import descriptionTypeLint from './description--type.ts';
 import contentValuesTypeLint from './content--values-type.ts';
 import contentRequiredLint from './content--required.ts';
 import requiredTypeLint from './required--type.ts';
+import $ref3RequestBodiesNamingLint from './$ref-3-0--request-bodies-naming.ts';
+import $ref3RequestBodiesNamingSchemaLint from './$ref-3-0--request-bodies-naming-schema.ts';
 
 const lints = [
+  $ref3RequestBodiesNamingLint,
+  $ref3RequestBodiesNamingSchemaLint,
   descriptionTypeLint,
   contentRequiredLint,
   contentValuesTypeLint,
diff --git a/packages/apidom-ls/src/config/openapi/schema/lint.ts b/packages/apidom-ls/src/config/openapi/schema/lint.ts
index 546fa7d593..d87f9b9671 100644
--- a/packages/apidom-ls/src/config/openapi/schema/lint.ts
+++ b/packages/apidom-ls/src/config/openapi/schema/lint.ts
@@ -75,6 +75,8 @@ import uniqueItemsNonArrayLint from '../../common/schema/lint/unique-items--non-
 import uniqueItemsTypeLint from '../../common/schema/lint/unique-items--type.ts';
 import writeOnlyTypeLint from '../../common/schema/lint/write-only--type.ts';
 import exampleDeprecatedLint from '../../common/schema/lint/example--deprecated.ts';
+import $refNotUsedLint from '../../common/schema/lint/$ref--not-used.ts';
+import $ref3RequestBodiesLint from '../../common/schema/lint/$ref-3-0--request-bodies.ts';
 import { OpenAPI31 } from '../target-specs.ts';
 
 const schemaLints = [
@@ -154,6 +156,8 @@ const schemaLints = [
   uniqueItemsTypeLint,
   writeOnlyTypeLint,
   exampleDeprecatedLint,
+  $refNotUsedLint,
+  $ref3RequestBodiesLint,
 ];
 
 export default schemaLints;
diff --git a/packages/apidom-ls/src/services/validation/linter-functions.ts b/packages/apidom-ls/src/services/validation/linter-functions.ts
index 196d248c27..3de5f1cda3 100644
--- a/packages/apidom-ls/src/services/validation/linter-functions.ts
+++ b/packages/apidom-ls/src/services/validation/linter-functions.ts
@@ -176,6 +176,20 @@ export const standardLinterfunctions: FunctionItem[] = [
       return true;
     },
   },
+  {
+    functionName: 'parentExistFields',
+    function: (element: Element, keys: string[]): boolean => {
+      const parent = element?.parent?.parent?.parent?.parent;
+      if (parent && isObject(parent)) {
+        for (const key of keys) {
+          if (!parent.hasKey(key)) {
+            return false;
+          }
+        }
+      }
+      return true;
+    },
+  },
   {
     functionName: 'existAnyOfFields',
     function: (element: Element, keys: string[], allowEmpty: boolean): boolean => {
@@ -1089,6 +1103,28 @@ export const standardLinterfunctions: FunctionItem[] = [
       return true;
     },
   },
+  {
+    functionName: 'apilintReferenceNotUsed',
+    function: (element: Element & { content?: { key?: string } }) => {
+      const elParent: Element = element.parent?.parent?.parent?.parent;
+      if (typeof elParent.hasKey !== 'function' || !elParent.hasKey('schemas')) {
+        return true;
+      }
+
+      const api = root(element);
+      const isReferenceElement = (el: Element & { content?: { key?: string } }) =>
+        toValue(el.content.key) === '$ref';
+      const referenceElements = filter((el) => {
+        return isReferenceElement(el);
+      }, api);
+      const referenceNames = referenceElements.map((refElement: Element) =>
+        // @ts-expect-error
+        toValue(refElement.content.value).split('/').at(-1),
+      );
+      // @ts-expect-error
+      return referenceNames.includes(toValue(element.parent.key));
+    },
+  },
   {
     functionName: 'apilintOpenAPIParameterInPathTemplate',
     function: (element: Element) => {
diff --git a/packages/apidom-ls/test/custom-rules.ts b/packages/apidom-ls/test/custom-rules.ts
index fbf1cb060f..0b814e5491 100644
--- a/packages/apidom-ls/test/custom-rules.ts
+++ b/packages/apidom-ls/test/custom-rules.ts
@@ -87,8 +87,8 @@ describe('apidom-ls-validate-custom-rules', function () {
       },
       {
         range: {
-          start: { line: 13, character: 8 },
-          end: { line: 13, character: 17 },
+          start: { line: 15, character: 8 },
+          end: { line: 15, character: 17 },
         },
         message: 'properties MUST follow camelCase',
         severity: 1,
@@ -98,8 +98,8 @@ describe('apidom-ls-validate-custom-rules', function () {
       },
       {
         range: {
-          start: { line: 18, character: 4 },
-          end: { line: 18, character: 7 },
+          start: { line: 20, character: 4 },
+          end: { line: 20, character: 7 },
         },
         message: 'Parameter Object must contain one of the following fields: content, schema',
         severity: 1,
@@ -118,8 +118,8 @@ describe('apidom-ls-validate-custom-rules', function () {
       },
       {
         range: {
-          start: { line: 20, character: 6 },
-          end: { line: 20, character: 10 },
+          start: { line: 22, character: 6 },
+          end: { line: 22, character: 10 },
         },
         message: 'parameter names MUST follow camelCase',
         severity: 1,
@@ -129,8 +129,8 @@ describe('apidom-ls-validate-custom-rules', function () {
       },
       {
         range: {
-          start: { line: 21, character: 4 },
-          end: { line: 21, character: 8 },
+          start: { line: 23, character: 4 },
+          end: { line: 23, character: 8 },
         },
         message: 'Parameter Object must contain one of the following fields: content, schema',
         severity: 1,
@@ -149,8 +149,8 @@ describe('apidom-ls-validate-custom-rules', function () {
       },
       {
         range: {
-          start: { line: 24, character: 4 },
-          end: { line: 24, character: 7 },
+          start: { line: 26, character: 4 },
+          end: { line: 26, character: 7 },
         },
         message: 'Parameter Object must contain one of the following fields: content, schema',
         severity: 1,
@@ -200,7 +200,7 @@ describe('apidom-ls-validate-custom-rules', function () {
     const result = await languageService.doValidation(docOpenapi, validationContext);
     const expected: Diagnostic[] = [
       {
-        range: { start: { line: 23, character: 6 }, end: { line: 23, character: 10 } },
+        range: { start: { line: 25, character: 6 }, end: { line: 25, character: 10 } },
         message: 'parameter names MUST follow camelCase',
         severity: 1,
         code: 20002,
@@ -208,7 +208,7 @@ describe('apidom-ls-validate-custom-rules', function () {
         data: {},
       },
       {
-        range: { start: { line: 32, character: 6 }, end: { line: 32, character: 10 } },
+        range: { start: { line: 34, character: 6 }, end: { line: 34, character: 10 } },
         message: 'parameter names MUST follow camelCase',
         severity: 1,
         code: 20002,
@@ -216,7 +216,7 @@ describe('apidom-ls-validate-custom-rules', function () {
         data: {},
       },
       {
-        range: { start: { line: 16, character: 8 }, end: { line: 16, character: 17 } },
+        range: { start: { line: 18, character: 8 }, end: { line: 18, character: 17 } },
         message: 'keys MUST follow camelCase',
         severity: 1,
         code: 20001,
@@ -224,7 +224,7 @@ describe('apidom-ls-validate-custom-rules', function () {
         data: {},
       },
       {
-        range: { start: { line: 31, character: 4 }, end: { line: 31, character: 7 } },
+        range: { start: { line: 33, character: 4 }, end: { line: 33, character: 7 } },
         message: 'keys MUST follow camelCase',
         severity: 1,
         code: 20001,
diff --git a/packages/apidom-ls/test/fixtures/custom-rules-jsonpath.yaml b/packages/apidom-ls/test/fixtures/custom-rules-jsonpath.yaml
index 0c75fee51b..8422270627 100644
--- a/packages/apidom-ls/test/fixtures/custom-rules-jsonpath.yaml
+++ b/packages/apidom-ls/test/fixtures/custom-rules-jsonpath.yaml
@@ -9,6 +9,8 @@ paths:
   /keb-ab:
     get:
       operationId: kebab      
+  /endpoint:
+    $ref: '#/components/schemas/User'
 components:
   schemas:
     User:
diff --git a/packages/apidom-ls/test/fixtures/custom-rules-simple.yaml b/packages/apidom-ls/test/fixtures/custom-rules-simple.yaml
index 2d20156918..b4a7e5afa3 100644
--- a/packages/apidom-ls/test/fixtures/custom-rules-simple.yaml
+++ b/packages/apidom-ls/test/fixtures/custom-rules-simple.yaml
@@ -6,6 +6,8 @@ paths:
   /keb-ab:
     get:
       operationId: kebab      
+  /endpoint:
+    $ref: '#/components/schemas/User'
 components:
   schemas:
     User:
diff --git a/packages/apidom-ls/test/fixtures/deref/invalid.json b/packages/apidom-ls/test/fixtures/deref/invalid.json
index 31409623f1..da5d524634 100644
--- a/packages/apidom-ls/test/fixtures/deref/invalid.json
+++ b/packages/apidom-ls/test/fixtures/deref/invalid.json
@@ -48,6 +48,11 @@
                 "schema": {
                   "$ref": "#/components/schemas/exampleRef"
                 }
+              },
+              "text/html": {
+                "schema": {
+                  "$ref": "#/components/schemas/petRef"
+                }
               }
             }
           }
diff --git a/packages/apidom-ls/test/fixtures/deref/valid-same-ref.json b/packages/apidom-ls/test/fixtures/deref/valid-same-ref.json
index c8edcc2b79..ae89e60014 100644
--- a/packages/apidom-ls/test/fixtures/deref/valid-same-ref.json
+++ b/packages/apidom-ls/test/fixtures/deref/valid-same-ref.json
@@ -4,6 +4,14 @@
     "title": "test",
     "version": "1.0"
   },
+  "paths": {
+    "/a": {
+      "$ref": "#/components/schemas/a"
+    },
+    "/b": {
+      "$ref": "#/components/schemas/b"
+    }
+  },
   "components": {
     "schemas": {
       "a": {
diff --git a/packages/apidom-ls/test/fixtures/validation/oas/ref-header.yaml b/packages/apidom-ls/test/fixtures/validation/oas/ref-header.yaml
new file mode 100644
index 0000000000..91390a8858
--- /dev/null
+++ b/packages/apidom-ls/test/fixtures/validation/oas/ref-header.yaml
@@ -0,0 +1,23 @@
+openapi: 3.0.0
+info:
+  version: 1.0.0
+  title: 'test'
+paths:
+  /foo:
+    get:
+      responses:
+        '200':
+          description: OK
+          headers:
+            X-MyHeader:
+              $ref: '#/components/schemas/MyHeader'
+components:
+  headers:
+    MyHeader:
+      description: ID of the user
+      required: true
+      schema:
+        type: string
+  schemas:
+    MyHeader:
+      description: ID of the user
diff --git a/packages/apidom-ls/test/fixtures/validation/oas/ref-not-used.yaml b/packages/apidom-ls/test/fixtures/validation/oas/ref-not-used.yaml
new file mode 100644
index 0000000000..69c14d6737
--- /dev/null
+++ b/packages/apidom-ls/test/fixtures/validation/oas/ref-not-used.yaml
@@ -0,0 +1,14 @@
+openapi: 3.0.0
+info:
+  title: 'test'
+  version: 1.0.0
+paths:
+  /test:
+    get:
+      responses:
+        default:
+          description: test
+components:
+  schemas:
+    notUsedSchema:
+      type: object
diff --git a/packages/apidom-ls/test/fixtures/validation/oas/ref-parameter.yaml b/packages/apidom-ls/test/fixtures/validation/oas/ref-parameter.yaml
new file mode 100644
index 0000000000..5195498bd5
--- /dev/null
+++ b/packages/apidom-ls/test/fixtures/validation/oas/ref-parameter.yaml
@@ -0,0 +1,16 @@
+openapi: 3.0.0
+info:
+  version: 1.0.0
+  title: 'test'
+paths:
+  /foo:
+    parameters:
+      - $ref: '#/components/headers/MyHeader'
+components:
+  headers:
+    MyHeader:
+      description: ID of the user
+      required: true
+      schema:
+        type: string
+
diff --git a/packages/apidom-ls/test/fixtures/validation/oas/ref-request-bodies-naming-schema.yaml b/packages/apidom-ls/test/fixtures/validation/oas/ref-request-bodies-naming-schema.yaml
new file mode 100644
index 0000000000..a1acea4592
--- /dev/null
+++ b/packages/apidom-ls/test/fixtures/validation/oas/ref-request-bodies-naming-schema.yaml
@@ -0,0 +1,23 @@
+openapi: 3.0.0
+info:
+  version: 1.0.0
+  title: 'test'
+paths:
+  /:
+    post:
+      responses:
+        default:
+          description: 'test'
+      operationId: myId
+      requestBody:
+        $ref: '#/components/schemas/MyBody'
+components:
+  schemas:
+    MyBody:
+      description: 'test'
+  requestBodies:
+    MyBody:
+      content:
+        application/json:
+          schema:
+            type: string
diff --git a/packages/apidom-ls/test/fixtures/validation/oas/ref-request-bodies-naming.yaml b/packages/apidom-ls/test/fixtures/validation/oas/ref-request-bodies-naming.yaml
new file mode 100644
index 0000000000..7844936188
--- /dev/null
+++ b/packages/apidom-ls/test/fixtures/validation/oas/ref-request-bodies-naming.yaml
@@ -0,0 +1,24 @@
+openapi: 3.0.0
+info:
+  version: 1.0.0
+  title: 'test'
+paths:
+  /:
+    post:
+      responses:
+        default:
+          description: 'test'
+      operationId: myId
+      requestBody:
+        $ref: '#/components/headers/MyBody'
+components:
+  headers:
+    MyBody:
+      schema:
+        description: 'description'
+  requestBodies:
+    MyBody:
+      content:
+        application/json:
+          schema:
+            type: string
diff --git a/packages/apidom-ls/test/fixtures/validation/oas/ref-request-bodies.yaml b/packages/apidom-ls/test/fixtures/validation/oas/ref-request-bodies.yaml
new file mode 100644
index 0000000000..495b508a99
--- /dev/null
+++ b/packages/apidom-ls/test/fixtures/validation/oas/ref-request-bodies.yaml
@@ -0,0 +1,23 @@
+openapi: 3.0.0
+info:
+  version: 1.0.0
+  title: 'test'
+paths:
+  /:
+    post:
+      responses:
+        default:
+          description: 'test'
+      operationId: myId
+      requestBody:
+        content:
+          application/json:
+            schema:
+              $ref: '#/components/requestBodies/MyBody/content/application~1json/schema'
+components:
+  requestBodies:
+    MyBody:
+      content:
+        application/json:
+          schema:
+            type: string
diff --git a/packages/apidom-ls/test/fixtures/validation/oas/valid/oas-3.0-petstore.yaml b/packages/apidom-ls/test/fixtures/validation/oas/valid/oas-3.0-petstore.yaml
index 43c1b2cf2a..6ad7526050 100644
--- a/packages/apidom-ls/test/fixtures/validation/oas/valid/oas-3.0-petstore.yaml
+++ b/packages/apidom-ls/test/fixtures/validation/oas/valid/oas-3.0-petstore.yaml
@@ -706,6 +706,8 @@ components:
           description: User Status
           format: int32
           example: 1
+        items:
+          $ref: '#/components/schemas/Customer'
       xml:
         name: user
     Tag:
diff --git a/packages/apidom-ls/test/fixtures/validation/oas/valid/oas-3.1-basic.yaml b/packages/apidom-ls/test/fixtures/validation/oas/valid/oas-3.1-basic.yaml
index 6f3df74a4c..8ad2a3a10e 100644
--- a/packages/apidom-ls/test/fixtures/validation/oas/valid/oas-3.1-basic.yaml
+++ b/packages/apidom-ls/test/fixtures/validation/oas/valid/oas-3.1-basic.yaml
@@ -25,6 +25,13 @@ paths:
           application/json:
             schema:
               $ref: '#/components/schemas/foo'
+    patch:
+      operationId: bpatch
+      requestBody:
+        content:
+          application/json:
+            schema:
+              $ref: '#/components/schemas/bar'
 components:
   schemas:
     foo:
diff --git a/packages/apidom-ls/test/openapi-json.ts b/packages/apidom-ls/test/openapi-json.ts
index 63ac92d4cb..a3273e4a50 100644
--- a/packages/apidom-ls/test/openapi-json.ts
+++ b/packages/apidom-ls/test/openapi-json.ts
@@ -512,6 +512,23 @@ describe('apidom-ls', function () {
         code: 7030101,
         source: 'apilint',
       },
+      {
+        code: 3240300,
+        data: {},
+        message: 'Definition was declared but never used in document',
+        range: {
+          end: {
+            character: 15,
+            line: 27,
+          },
+          start: {
+            character: 6,
+            line: 27,
+          },
+        },
+        severity: 2,
+        source: 'apilint',
+      },
       {
         range: { start: { line: 30, character: 10 }, end: { line: 30, character: 14 } },
         message: 'Schema does not include any Schema Object keywords',
diff --git a/packages/apidom-ls/test/openapi-yaml.ts b/packages/apidom-ls/test/openapi-yaml.ts
index a4f68efaae..975e199f70 100644
--- a/packages/apidom-ls/test/openapi-yaml.ts
+++ b/packages/apidom-ls/test/openapi-yaml.ts
@@ -520,6 +520,23 @@ describe('apidom-ls-yaml', function () {
         code: 7030101,
         source: 'apilint',
       },
+      {
+        code: 3240300,
+        data: {},
+        message: 'Definition was declared but never used in document',
+        range: {
+          end: {
+            character: 11,
+            line: 25,
+          },
+          start: {
+            character: 4,
+            line: 25,
+          },
+        },
+        severity: 2,
+        source: 'apilint',
+      },
       {
         range: { start: { line: 28, character: 8 }, end: { line: 28, character: 10 } },
         message: 'Schema does not include any Schema Object keywords',
diff --git a/packages/apidom-ls/test/validate-references.ts b/packages/apidom-ls/test/validate-references.ts
index b6a5a22020..0efd8013ce 100644
--- a/packages/apidom-ls/test/validate-references.ts
+++ b/packages/apidom-ls/test/validate-references.ts
@@ -114,7 +114,7 @@ describe('reference validation', function () {
           },
         },
         {
-          range: { start: { line: 63, character: 16 }, end: { line: 63, character: 99 } },
+          range: { start: { line: 68, character: 16 }, end: { line: 68, character: 99 } },
           message:
             'Reference Error - JSONPointerKeyError: Invalid object key "PetInvalid" at position 2 in "/components/schemas/PetInvalid": key not found in object',
           severity: 1,
@@ -214,7 +214,7 @@ describe('reference validation', function () {
             },
           },
           {
-            range: { start: { line: 63, character: 16 }, end: { line: 63, character: 99 } },
+            range: { start: { line: 68, character: 16 }, end: { line: 68, character: 99 } },
             message:
               'Reference Error - JSONPointerKeyError: Invalid object key "PetInvalid" at position 2 in "/components/schemas/PetInvalid": key not found in object',
             severity: 1,
diff --git a/packages/apidom-ls/test/validate.ts b/packages/apidom-ls/test/validate.ts
index fb4564857a..1c379f7f45 100644
--- a/packages/apidom-ls/test/validate.ts
+++ b/packages/apidom-ls/test/validate.ts
@@ -3001,6 +3001,320 @@ describe('apidom-ls-validate', function () {
     languageService.terminate();
   });
 
+  it('oas / yaml - ref is defined but not used', async function () {
+    const validationContext: ValidationContext = {
+      comments: DiagnosticSeverity.Error,
+      maxNumberOfProblems: 100,
+      relatedInformation: false,
+    };
+
+    const spec = fs
+      .readFileSync(path.join(__dirname, 'fixtures', 'validation', 'oas', 'ref-not-used.yaml'))
+      .toString();
+    const doc: TextDocument = TextDocument.create('foo://bar/ref-not-used.yaml', 'yaml', 0, spec);
+
+    const languageService: LanguageService = getLanguageService(contextNoSchema);
+
+    const result = await languageService.doValidation(doc, validationContext);
+    result[0].code = 'test';
+    const expected: Diagnostic[] = [
+      {
+        range: { start: { line: 12, character: 4 }, end: { line: 12, character: 17 } },
+        message: 'Definition was declared but never used in document',
+        severity: 2,
+        code: 'test',
+        source: 'apilint',
+        data: {},
+      },
+    ];
+    assert.deepEqual(result, expected as Diagnostic[]);
+
+    languageService.terminate();
+  });
+
+  it('oas 3.0 / yaml - requestBody $refs must point to a position where can be legally placed', async function () {
+    const validationContext: ValidationContext = {
+      comments: DiagnosticSeverity.Error,
+      maxNumberOfProblems: 100,
+      relatedInformation: false,
+    };
+
+    const spec = fs
+      .readFileSync(
+        path.join(__dirname, 'fixtures', 'validation', 'oas', 'ref-request-bodies.yaml'),
+      )
+      .toString();
+    const doc: TextDocument = TextDocument.create(
+      'foo://bar/ref-request-bodies.yaml',
+      'yaml',
+      0,
+      spec,
+    );
+
+    const languageService: LanguageService = getLanguageService(contextNoSchema);
+
+    const result = await languageService.doValidation(doc, validationContext);
+    result[0].code = 'test';
+    const expected: Diagnostic[] = [
+      {
+        range: { start: { line: 15, character: 20 }, end: { line: 15, character: 88 } },
+        message:
+          'requestBody schema $refs must point to a position where a Schema Object can be legally placed',
+        severity: 1,
+        code: 'test',
+        source: 'apilint',
+        data: {},
+      },
+    ];
+    assert.deepEqual(result, expected as Diagnostic[]);
+
+    languageService.terminate();
+  });
+
+  it('oas 3.0 / yaml - requestBody $refs must point to a position naming', async function () {
+    const validationContext: ValidationContext = {
+      comments: DiagnosticSeverity.Error,
+      maxNumberOfProblems: 100,
+      relatedInformation: false,
+    };
+
+    const spec = fs
+      .readFileSync(
+        path.join(__dirname, 'fixtures', 'validation', 'oas', 'ref-request-bodies-naming.yaml'),
+      )
+      .toString();
+    const doc: TextDocument = TextDocument.create(
+      'foo://bar/ref-request-bodies-naming.yaml',
+      'yaml',
+      0,
+      spec,
+    );
+
+    const languageService: LanguageService = getLanguageService(contextNoSchema);
+
+    const result = await languageService.doValidation(doc, validationContext);
+    result[0].code = 'test';
+    result[1].code = 'test';
+    const expected: Diagnostic[] = [
+      {
+        range: { start: { line: 12, character: 14 }, end: { line: 12, character: 43 } },
+        message: 'local reference not found',
+        severity: 1,
+        code: 'test',
+        source: 'apilint',
+        data: {
+          quickFix: [
+            {
+              message: 'update to #/components/requestBodies/MyBody',
+              action: 'updateValue',
+              functionParams: ['#/components/requestBodies/MyBody'],
+            },
+          ],
+        },
+      },
+      {
+        range: { start: { line: 12, character: 14 }, end: { line: 12, character: 43 } },
+        message:
+          'requestBody $refs must point to a position where a requestBody can be legally placed',
+        severity: 1,
+        code: 'test',
+        source: 'apilint',
+        data: {},
+      },
+    ];
+    assert.deepEqual(result, expected as Diagnostic[]);
+
+    languageService.terminate();
+  });
+
+  it('oas 3.0 / yaml - requestBody $refs must point to a position naming schema', async function () {
+    const validationContext: ValidationContext = {
+      comments: DiagnosticSeverity.Error,
+      maxNumberOfProblems: 100,
+      relatedInformation: false,
+    };
+
+    const spec = fs
+      .readFileSync(
+        path.join(
+          __dirname,
+          'fixtures',
+          'validation',
+          'oas',
+          'ref-request-bodies-naming-schema.yaml',
+        ),
+      )
+      .toString();
+    const doc: TextDocument = TextDocument.create(
+      'foo://bar/ref-request-bodies-naming-schema.yaml',
+      'yaml',
+      0,
+      spec,
+    );
+
+    const languageService: LanguageService = getLanguageService(contextNoSchema);
+
+    const result = await languageService.doValidation(doc, validationContext);
+    result[0].code = 'test';
+    result[1].code = 'test';
+    const expected: Diagnostic[] = [
+      {
+        range: { start: { line: 12, character: 14 }, end: { line: 12, character: 43 } },
+        message: 'local reference not found',
+        severity: 1,
+        code: 'test',
+        source: 'apilint',
+        data: {
+          quickFix: [
+            {
+              message: 'update to #/components/requestBodies/MyBody',
+              action: 'updateValue',
+              functionParams: ['#/components/requestBodies/MyBody'],
+            },
+          ],
+        },
+      },
+      {
+        range: { start: { line: 12, character: 14 }, end: { line: 12, character: 43 } },
+        message:
+          "requestBody $refs cannot point to '#/components/schemas/…', they must point to '#/components/requestBodies/…'",
+        severity: 1,
+        code: 'test',
+        source: 'apilint',
+        data: {},
+      },
+    ];
+    assert.deepEqual(result, expected as Diagnostic[]);
+
+    languageService.terminate();
+  });
+
+  it('oas 3.0 / yaml - OAS3 header $Ref should point to Header Object', async function () {
+    const validationContext: ValidationContext = {
+      comments: DiagnosticSeverity.Error,
+      maxNumberOfProblems: 100,
+      relatedInformation: false,
+    };
+
+    const spec = fs
+      .readFileSync(path.join(__dirname, 'fixtures', 'validation', 'oas', 'ref-header.yaml'))
+      .toString();
+    const doc: TextDocument = TextDocument.create('foo://bar/ref-header.yaml', 'yaml', 0, spec);
+
+    const languageService: LanguageService = getLanguageService(contextNoSchema);
+    const result = await languageService.doValidation(doc, validationContext);
+
+    result[0].code = 'test';
+
+    const expected: Diagnostic[] = [
+      {
+        code: 'test',
+        data: {
+          quickFix: [
+            {
+              action: 'updateValue',
+              functionParams: ['#/components/headers/MyHeader'],
+              message: 'update to #/components/headers/MyHeader',
+            },
+          ],
+        },
+        message: 'local reference not found',
+        range: {
+          end: {
+            character: 51,
+            line: 12,
+          },
+          start: {
+            character: 20,
+            line: 12,
+          },
+        },
+        severity: 1,
+        source: 'apilint',
+      },
+      {
+        code: 5260300,
+        data: {},
+        message: 'OAS3 header $Ref should point to Header Object',
+        range: {
+          end: {
+            character: 51,
+            line: 12,
+          },
+          start: {
+            character: 20,
+            line: 12,
+          },
+        },
+        severity: 1,
+        source: 'apilint',
+      },
+    ];
+    assert.deepEqual(result, expected as Diagnostic[]);
+
+    languageService.terminate();
+  });
+
+  it('oas 3.0 / yaml - OAS3 parameter $Ref should point to Parameter Object', async function () {
+    const validationContext: ValidationContext = {
+      comments: DiagnosticSeverity.Error,
+      maxNumberOfProblems: 100,
+      relatedInformation: false,
+    };
+
+    const spec = fs
+      .readFileSync(path.join(__dirname, 'fixtures', 'validation', 'oas', 'ref-parameter.yaml'))
+      .toString();
+    const doc: TextDocument = TextDocument.create('foo://bar/ref-parameter.yaml', 'yaml', 0, spec);
+
+    const languageService: LanguageService = getLanguageService(contextNoSchema);
+    const result = await languageService.doValidation(doc, validationContext);
+
+    result[0].code = 'test';
+
+    const expected: Diagnostic[] = [
+      {
+        code: 'test',
+        data: {
+          quickFix: [],
+        },
+        message: 'local reference not found',
+        range: {
+          end: {
+            character: 45,
+            line: 7,
+          },
+          start: {
+            character: 14,
+            line: 7,
+          },
+        },
+        severity: 1,
+        source: 'apilint',
+      },
+      {
+        code: 5260400,
+        data: {},
+        message: 'OAS3 parameter $Ref should point to Parameter Object',
+        range: {
+          end: {
+            character: 45,
+            line: 7,
+          },
+          start: {
+            character: 14,
+            line: 7,
+          },
+        },
+        severity: 1,
+        source: 'apilint',
+      },
+    ];
+    assert.deepEqual(result, expected as Diagnostic[]);
+
+    languageService.terminate();
+  });
+
   it('oas / yaml - test editor issue 3626 / inidrect ref', async function () {
     const validationContext: ValidationContext = {
       comments: DiagnosticSeverity.Error,
@@ -3022,7 +3336,25 @@ describe('apidom-ls-validate', function () {
 
     const result = await languageService.doValidation(doc, validationContext);
     result[0].code = 'test';
+    result[1].code = 'test';
     const expected: Diagnostic[] = [
+      {
+        code: 'test',
+        data: {},
+        message: 'Definition was declared but never used in document',
+        range: {
+          end: {
+            character: 7,
+            line: 31,
+          },
+          start: {
+            character: 4,
+            line: 31,
+          },
+        },
+        severity: 2,
+        source: 'apilint',
+      },
       {
         range: { start: { line: 39, character: 12 }, end: { line: 39, character: 50 } },
         message: 'local reference not found',
@@ -3173,6 +3505,14 @@ describe('apidom-ls-validate', function () {
           ],
         },
       },
+      {
+        range: { start: { line: 10, character: 4 }, end: { line: 10, character: 7 } },
+        message: 'Definition was declared but never used in document',
+        severity: 2,
+        code: 3240300,
+        source: 'apilint',
+        data: {},
+      },
     ];
     assert.deepEqual(result, expected as Diagnostic[]);