diff --git a/tools/dgeni/common/decorators.ts b/tools/dgeni/common/decorators.ts
index 7f9785960bab..86a10b1acac6 100644
--- a/tools/dgeni/common/decorators.ts
+++ b/tools/dgeni/common/decorators.ts
@@ -3,19 +3,20 @@ import {ClassExportDoc} from 'dgeni-packages/typescript/api-doc-types/ClassExpor
 import {MemberDoc} from 'dgeni-packages/typescript/api-doc-types/MemberDoc';
 import {PropertyMemberDoc} from 'dgeni-packages/typescript/api-doc-types/PropertyMemberDoc';
 import {CategorizedClassDoc, DeprecationInfo, HasDecoratorsDoc} from './dgeni-definitions';
+import {findJsDocTag, hasJsDocTag} from './tags';
 
-export function isMethod(doc: MemberDoc) {
+export function isMethod(doc: MemberDoc): boolean {
   return doc.hasOwnProperty('parameters') && !doc.isGetAccessor && !doc.isSetAccessor;
 }
 
-export function isGenericTypeParameter(doc: MemberDoc) {
+export function isGenericTypeParameter(doc: MemberDoc): boolean {
   if (doc.containerDoc instanceof ClassExportDoc) {
-    return doc.containerDoc.typeParams && `<${doc.name}>` === doc.containerDoc.typeParams;
+    return !!doc.containerDoc.typeParams && `<${doc.name}>` === doc.containerDoc.typeParams;
   }
   return false;
 }
 
-export function isProperty(doc: MemberDoc) {
+export function isProperty(doc: MemberDoc): boolean {
   if (
     doc instanceof PropertyMemberDoc ||
     // The latest Dgeni version no longer treats getters or setters as properties.
@@ -28,30 +29,28 @@ export function isProperty(doc: MemberDoc) {
   return false;
 }
 
-export function isDirective(doc: ClassExportDoc) {
+export function isDirective(doc: ClassExportDoc): boolean {
   return hasClassDecorator(doc, 'Component') || hasClassDecorator(doc, 'Directive');
 }
 
-export function isService(doc: ClassExportDoc) {
+export function isService(doc: ClassExportDoc): boolean {
   return hasClassDecorator(doc, 'Injectable');
 }
 
-export function isNgModule(doc: ClassExportDoc) {
+export function isNgModule(doc: ClassExportDoc): boolean {
   return hasClassDecorator(doc, 'NgModule');
 }
 
-export function isDeprecatedDoc(doc: any) {
-  return ((doc.tags && doc.tags.tags) || []).some((tag: any) => tag.tagName === 'deprecated');
+export function isDeprecatedDoc(doc: ApiDoc): boolean {
+  return hasJsDocTag(doc, 'deprecated');
 }
 
 /** Whether the given document is annotated with the "@docs-primary-export" jsdoc tag. */
-export function isPrimaryExportDoc(doc: any) {
-  return ((doc.tags && doc.tags.tags) || []).some(
-    (tag: any) => tag.tagName === 'docs-primary-export',
-  );
+export function isPrimaryExportDoc(doc: ApiDoc): boolean {
+  return hasJsDocTag(doc, 'docs-primary-export');
 }
 
-export function getDirectiveSelectors(classDoc: CategorizedClassDoc) {
+export function getDirectiveSelectors(classDoc: CategorizedClassDoc): string[] | undefined {
   if (classDoc.directiveMetadata) {
     const directiveSelectors: string = classDoc.directiveMetadata.get('selector');
 
@@ -65,15 +64,15 @@ export function getDirectiveSelectors(classDoc: CategorizedClassDoc) {
   return undefined;
 }
 
-export function hasMemberDecorator(doc: MemberDoc, decoratorName: string) {
+export function hasMemberDecorator(doc: MemberDoc, decoratorName: string): boolean {
   return doc.docType == 'member' && hasDecorator(doc, decoratorName);
 }
 
-export function hasClassDecorator(doc: ClassExportDoc, decoratorName: string) {
+export function hasClassDecorator(doc: ClassExportDoc, decoratorName: string): boolean {
   return doc.docType == 'class' && hasDecorator(doc, decoratorName);
 }
 
-export function hasDecorator(doc: HasDecoratorsDoc, decoratorName: string) {
+export function hasDecorator(doc: HasDecoratorsDoc, decoratorName: string): boolean {
   return (
     !!doc.decorators &&
     doc.decorators.length > 0 &&
@@ -81,12 +80,8 @@ export function hasDecorator(doc: HasDecoratorsDoc, decoratorName: string) {
   );
 }
 
-export function getBreakingChange(doc: any): string | null {
-  if (!doc.tags) {
-    return null;
-  }
-
-  const breakingChange = doc.tags.tags.find((t: any) => t.tagName === 'breaking-change');
+export function getBreakingChange(doc: ApiDoc): string | null {
+  const breakingChange = findJsDocTag(doc, 'breaking-change');
   return breakingChange ? breakingChange.description : null;
 }
 
diff --git a/tools/dgeni/common/private-docs.ts b/tools/dgeni/common/private-docs.ts
index 435a213db99f..76ecdb4d7cde 100644
--- a/tools/dgeni/common/private-docs.ts
+++ b/tools/dgeni/common/private-docs.ts
@@ -1,6 +1,7 @@
 import {ApiDoc} from 'dgeni-packages/typescript/api-doc-types/ApiDoc';
 import {MemberDoc} from 'dgeni-packages/typescript/api-doc-types/MemberDoc';
 import {isInheritanceCreatedDoc} from './class-inheritance';
+import {findJsDocTag, hasJsDocTag, Tag} from './tags';
 
 const INTERNAL_METHODS = [
   // Lifecycle methods
@@ -48,20 +49,18 @@ export function isPublicDoc(doc: ApiDoc) {
 }
 
 /** Gets the @docs-public tag from the given document if present. */
-export function getDocsPublicTag(doc: any): {tagName: string; description: string} | undefined {
-  const tags = doc.tags && doc.tags.tags;
-  return tags ? tags.find((d: any) => d.tagName == 'docs-public') : undefined;
+export function getDocsPublicTag(doc: ApiDoc): Tag | undefined {
+  return findJsDocTag(doc, 'docs-public');
 }
 
 /** Whether the given method member is listed as an internal member. */
-function _isInternalMember(memberDoc: MemberDoc) {
+function _isInternalMember(memberDoc: MemberDoc): boolean {
   return INTERNAL_METHODS.includes(memberDoc.name);
 }
 
 /** Whether the given doc has a @docs-private tag set. */
-function _hasDocsPrivateTag(doc: any) {
-  const tags = doc.tags && doc.tags.tags;
-  return tags ? tags.find((d: any) => d.tagName == 'docs-private') : false;
+function _hasDocsPrivateTag(doc: ApiDoc): boolean {
+  return hasJsDocTag(doc, 'docs-private');
 }
 
 /**
@@ -73,6 +72,6 @@ function _hasDocsPrivateTag(doc: any) {
  * split up into several base classes to support the MDC prototypes. e.g. "_MatMenu" should
  * show up in the docs as "MatMenu".
  */
-function _isEnforcedPublicDoc(doc: any): boolean {
+function _isEnforcedPublicDoc(doc: ApiDoc): boolean {
   return getDocsPublicTag(doc) !== undefined;
 }
diff --git a/tools/dgeni/common/tags.ts b/tools/dgeni/common/tags.ts
new file mode 100644
index 000000000000..cedf0be3c49a
--- /dev/null
+++ b/tools/dgeni/common/tags.ts
@@ -0,0 +1,72 @@
+import {ApiDoc} from 'dgeni-packages/typescript/api-doc-types/ApiDoc';
+
+/**
+ * Type describing a collection of tags, matching with the objects
+ * created by the Dgeni JSDoc processors.
+ *
+ * https://github.com/angular/dgeni-packages/blob/19e629c0d156572cbea149af9e0cc7ec02db7cb6/jsdoc/lib/TagCollection.js#L4
+ */
+export interface TagCollection {
+  /** List of tags. */
+  tags: Tag[];
+  /** Map which maps tag names to their tag instances. */
+  tagsByName: Map<string, Tag[]>;
+  /** List of tags which are unkown, or have errors. */
+  badTags: Tag[];
+}
+
+/**
+ * Type describing a tag, matching with the objects created by the
+ * Dgeni JSDoc processors.
+ *
+ * https://github.com/angular/dgeni-packages/blob/19e629c0d156572cbea149af9e0cc7ec02db7cb6/jsdoc/lib/Tag.js#L1
+ */
+export interface Tag {
+  /** Definition of the tag. Undefined if the tag is unknown. */
+  tagDef: undefined | TagDefinition;
+  /** Name of the tag (excluding the `@`) */
+  tagName: string;
+  /** Description associated with the tag. */
+  description: string;
+  /** Source file line where this tag starts. */
+  startingLine: number;
+  /** Optional list of errors that have been computed for this tag. */
+  errors?: string[];
+}
+
+/** Type describing a tag definition for the Dgeni JSDoc processor. */
+export interface TagDefinition {
+  /** Name of the tag (excluding the `@`) */
+  name: string;
+  /** Property where the tag information should be attached to. */
+  docProperty?: string;
+  /** Whether multiple instances of the tag can be used in the same comment. */
+  multi?: boolean;
+  /** Whether this tag is required for all API documents. */
+  required?: boolean;
+}
+
+/** Type describing an API doc with JSDoc tag information. */
+export type ApiDocWithJsdocTags = ApiDoc & {
+  /** Collection of JSDoc tags attached to this API document. */
+  tags: TagCollection;
+};
+
+/** Whether the specified API document has JSDoc tag information attached. */
+export function isApiDocWithJsdocTags(doc: ApiDoc): doc is ApiDocWithJsdocTags {
+  return (doc as Partial<ApiDocWithJsdocTags>).tags !== undefined;
+}
+
+/** Finds the specified JSDoc tag within the given API doc. */
+export function findJsDocTag(doc: ApiDoc, tagName: string): Tag | undefined {
+  if (!isApiDocWithJsdocTags(doc)) {
+    return undefined;
+  }
+
+  return doc.tags.tags.find(t => t.tagName === tagName);
+}
+
+/** Gets whether the specified API doc has a given JSDoc tag. */
+export function hasJsDocTag(doc: ApiDoc, tagName: string): boolean {
+  return findJsDocTag(doc, tagName) !== undefined;
+}
diff --git a/tools/dgeni/docs-package.ts b/tools/dgeni/docs-package.ts
index 8e047bc8ad30..c006065849b2 100644
--- a/tools/dgeni/docs-package.ts
+++ b/tools/dgeni/docs-package.ts
@@ -8,6 +8,7 @@ import {AsyncFunctionsProcessor} from './processors/async-functions';
 import {categorizer} from './processors/categorizer';
 import {DocsPrivateFilter} from './processors/docs-private-filter';
 import {EntryPointGrouper} from './processors/entry-point-grouper';
+import {ErrorUnknownJsdocTagsProcessor} from './processors/error-unknown-jsdoc-tags';
 import {FilterDuplicateExports} from './processors/filter-duplicate-exports';
 import {mergeInheritedProperties} from './processors/merge-inherited-properties';
 import {resolveInheritedDocs} from './processors/resolve-inherited-docs';
@@ -51,6 +52,9 @@ apiDocsPackage.processor(mergeInheritedProperties);
 // Processor that filters out symbols that should not be shown in the docs.
 apiDocsPackage.processor(new DocsPrivateFilter());
 
+// Processor that throws an error if API docs with unknown JSDoc tags are discovered.
+apiDocsPackage.processor(new ErrorUnknownJsdocTagsProcessor());
+
 // Processor that appends categorization flags to the docs, e.g. `isDirective`, `isNgModule`, etc.
 apiDocsPackage.processor(categorizer);
 
@@ -100,6 +104,15 @@ apiDocsPackage.config(function (parseTagsProcessor: any) {
     {name: 'template', multi: true},
     //  JSDoc annotations/tags which are not supported by default.
     {name: 'throws', multi: true},
+
+    // Annotations/tags from external API docs (i.e. from the node modules). These tags are
+    // added so that no errors are reported.
+    // TODO(devversion): remove this once the fix in dgeni-package is available.
+    //   https://github.com/angular/dgeni-packages/commit/19e629c0d156572cbea149af9e0cc7ec02db7cb6.
+    {name: 'usageNotes'},
+    {name: 'publicApi'},
+    {name: 'ngModule', multi: true},
+    {name: 'nodoc'},
   ]);
 });
 
diff --git a/tools/dgeni/processors/error-unknown-jsdoc-tags.ts b/tools/dgeni/processors/error-unknown-jsdoc-tags.ts
new file mode 100644
index 000000000000..e1e1e28d9827
--- /dev/null
+++ b/tools/dgeni/processors/error-unknown-jsdoc-tags.ts
@@ -0,0 +1,38 @@
+import {DocCollection, Processor} from 'dgeni';
+import {isApiDocWithJsdocTags} from '../common/tags';
+
+/**
+ * Processor that checks API docs for unknown JSDoc tags. Dgeni by default will
+ * warn about unknown tags. This processor will throw an error instead.
+ */
+export class ErrorUnknownJsdocTagsProcessor implements Processor {
+  name = 'error-unknown-tags';
+  $runAfter = ['docs-private-filter'];
+  $runBefore = ['categorizer'];
+
+  $process(docs: DocCollection) {
+    for (const doc of docs) {
+      if (!isApiDocWithJsdocTags(doc)) {
+        continue;
+      }
+
+      if (doc.tags.badTags.length > 0) {
+        let errorMessage = `Found errors for processed JSDoc comments in ${doc.id}:\n`;
+
+        for (const tag of doc.tags.badTags) {
+          errorMessage += '\n';
+
+          if (tag.tagDef === undefined) {
+            errorMessage += `  * Tag "${tag.tagName}": Unknown tag.\n`;
+          }
+
+          for (const concreteError of tag.errors ?? []) {
+            errorMessage += `  * Tag "${tag.tagName}": ${concreteError}\n`;
+          }
+        }
+
+        throw new Error(errorMessage);
+      }
+    }
+  }
+}
diff --git a/tools/dgeni/processors/resolve-inherited-docs.ts b/tools/dgeni/processors/resolve-inherited-docs.ts
index 880b8be83d54..9ee0a2c81bde 100644
--- a/tools/dgeni/processors/resolve-inherited-docs.ts
+++ b/tools/dgeni/processors/resolve-inherited-docs.ts
@@ -20,6 +20,9 @@ export function resolveInheritedDocs(exportSymbolsToDocsMap: Map<ts.Symbol, Clas
  * processed by other standard processors in the Dgeni pipeline. This is helpful as
  * API documents for inheritance are created manually if not exported, and we'd want
  * such docs to be processed by the Dgeni JSDoc processor for example.
+ *
+ * Note that we also want to include external API docs (e.g. from the node modules)
+ * since members from those can also be merged with public-facing API docs.
  */
 export class ResolveInheritedDocs implements Processor {
   $runBefore = ['docs-private-filter', 'parsing-tags'];
@@ -44,14 +47,6 @@ export class ResolveInheritedDocs implements Processor {
         if (!isInheritanceCreatedDoc(apiDoc)) {
           return;
         }
-        // If this is an external document not part of our sources, we will not add it to the
-        // Dgeni API doc pipeline. Docs would be filtered regardless, but adding them to the
-        // pipeline could cause e.g. the JSDoc parser to complain about tags/annotations which
-        // are not known/relevant to our API docs. e.g. Framework uses `@nodoc` or `@usageNotes`.
-        if (apiDoc.fileInfo.projectRelativePath.startsWith('../')) {
-          return;
-        }
-
         // Add the member docs for the inherited doc to the Dgeni doc collection.
         this._getContainingMemberDocs(apiDoc).forEach(d => newDocs.add(d));
         // Add the class-like export doc to the Dgeni doc collection.