diff --git a/.changeset/diff-parser-error-empty-message.md b/.changeset/diff-parser-error-empty-message.md
new file mode 100644
index 000000000..81e2d45bd
--- /dev/null
+++ b/.changeset/diff-parser-error-empty-message.md
@@ -0,0 +1,10 @@
+---
+'@asyncapi/cli': patch
+---
+
+Fix `asyncapi diff` printing a bare `ValidationError:` with no diagnostic body
+when one of the supplied documents fails to parse. The parse-failure branch in
+`parseDocuments` used the `'invalid-file'` ValidationError type (the file-not-
+found template) instead of `'parser-error'`, and `buildError` produced an
+empty string for non-ParserError error shapes such as plain strings or generic
+`Error` objects. Both paths now surface a meaningful, non-empty message.
diff --git a/src/apps/cli/commands/diff.ts b/src/apps/cli/commands/diff.ts
index c76687c8a..9e18bb983 100644
--- a/src/apps/cli/commands/diff.ts
+++ b/src/apps/cli/commands/diff.ts
@@ -247,7 +247,7 @@ export default class Diff extends Command {
     if (!firstResult.success || !secondResult.success) {
       this.error(
         new ValidationError({
-          type: 'invalid-file',
+          type: 'parser-error',
           filepath: firstDocument.getFilePath() || secondDocument.getFilePath(),
           err: firstResult.error || secondResult.error,
         }),
diff --git a/src/errors/validation-error.ts b/src/errors/validation-error.ts
index 71dc7b7e1..2582a44d6 100644
--- a/src/errors/validation-error.ts
+++ b/src/errors/validation-error.ts
@@ -30,40 +30,69 @@ export class ValidationError extends Error {
   }
 
   private buildError(err: any) {
-    const errorsInfo: Array<string> = [];
+    const errorsInfo = collectParserErrorInfo(err);
 
-    if (err.title) {
-      errorsInfo.push(err.title);
+    if (errorsInfo.length > 0) {
+      this.message = errorsInfo.join('\n');
+      return;
     }
 
-    if (err.detail) {
-      errorsInfo.push(err.details);
-    }
+    // Fallback for error shapes that don't follow the @asyncapi/parser
+    // ParserError contract (plain strings, generic Errors, undefined): surface
+    // the most informative non-empty value we can find so callers never see a
+    // bare "ValidationError:" with no diagnostic body.
+    this.message =
+      (typeof err === 'string' && err) ||
+      err?.message ||
+      err?.title ||
+      'Unknown parser error';
+  }
+}
 
-    if (err.validationErrors) {
-      for (const e of err.validationErrors) {
-        const errorHasTitle = !!e.title;
-        const errorHasLocation = !!e.location;
-        /*
-         * All the conditions below are needed since validationErrors (from ParserError) come from Parser JS library,
-         * so we cannot assure that all the fields or properties are always provided in the error. There might be cases
-         * that even title is not provided.
-         */
-        if (errorHasTitle && errorHasLocation) {
-          errorsInfo.push(
-            `${e.title} ${e.location.startLine}:${e.location.startColumn}`,
-          );
-          continue;
-        }
-        if (errorHasTitle) {
-          errorsInfo.push(`${e.title}`);
-          continue;
-        }
-        if (errorHasLocation) {
-          errorsInfo.push(`${e.location.startLine}:${e.location.startColumn}`);
-        }
+function collectParserErrorInfo(err: any): string[] {
+  const errorsInfo: string[] = [];
+
+  if (!err) {
+    return errorsInfo;
+  }
+
+  if (err.title) {
+    errorsInfo.push(err.title);
+  }
+
+  if (err.detail) {
+    errorsInfo.push(err.details);
+  }
+
+  if (err.validationErrors) {
+    for (const e of err.validationErrors) {
+      const formatted = formatValidationError(e);
+      if (formatted) {
+        errorsInfo.push(formatted);
       }
     }
-    this.message = errorsInfo.join('\n');
   }
+
+  return errorsInfo;
+}
+
+/*
+ * Format a single ParserError validationErrors entry. All fields are
+ * defensive: validationErrors come from the @asyncapi/parser JS library and
+ * are not guaranteed to provide a title or a location.
+ */
+function formatValidationError(e: any): string | undefined {
+  const errorHasTitle = !!e.title;
+  const errorHasLocation = !!e.location;
+
+  if (errorHasTitle && errorHasLocation) {
+    return `${e.title} ${e.location.startLine}:${e.location.startColumn}`;
+  }
+  if (errorHasTitle) {
+    return `${e.title}`;
+  }
+  if (errorHasLocation) {
+    return `${e.location.startLine}:${e.location.startColumn}`;
+  }
+  return undefined;
 }
diff --git a/test/integration/diff.test.ts b/test/integration/diff.test.ts
index 5befd309c..1a6c38a7b 100644
--- a/test/integration/diff.test.ts
+++ b/test/integration/diff.test.ts
@@ -577,4 +577,19 @@ describe('diff', () => {
         });
     });
   });
+
+  describe('when one of the documents cannot be parsed', () => {
+    test
+      .stderr()
+      .stdout()
+      .command(['diff', './test/fixtures/specification.yml', './test/fixtures/specification-invalid.yml'])
+      .it('surfaces a non-empty ValidationError message instead of a bare "ValidationError:"', (ctx, done) => {
+        expect(ctx.stderr).to.contain('ValidationError');
+        // The historical bug emitted a literal "ValidationError:" with no
+        // diagnostic body; ensure at least one informative token follows.
+        expect(ctx.stderr).to.not.match(/ValidationError:\s*\n/);
+        expect(ctx.stderr).to.contain('parse');
+        done();
+      });
+  });
 });
diff --git a/test/unit/errors/validation-error.test.ts b/test/unit/errors/validation-error.test.ts
new file mode 100644
index 000000000..e7203bd13
--- /dev/null
+++ b/test/unit/errors/validation-error.test.ts
@@ -0,0 +1,88 @@
+import { expect } from 'chai';
+import { ValidationError } from '../../../src/errors/validation-error';
+
+describe('ValidationError', () => {
+  describe('type: parser-error', () => {
+    it('formats validationErrors with title and location', () => {
+      const error = new ValidationError({
+        type: 'parser-error',
+        err: {
+          title: 'Validation failed',
+          validationErrors: [
+            { title: 'Missing required field', location: { startLine: 3, startColumn: 5 } },
+            { title: 'Invalid type' },
+          ],
+        },
+      });
+
+      expect(error.message).to.contain('Validation failed');
+      expect(error.message).to.contain('Missing required field 3:5');
+      expect(error.message).to.contain('Invalid type');
+    });
+
+    it('falls back to the string err itself when no ParserError fields are present', () => {
+      // Validation service returns errors as plain strings (e.g. "Failed to
+      // parse document"). Without the fallback, buildError produced an empty
+      // message and the user saw a bare "ValidationError:" with no body.
+      const error = new ValidationError({
+        type: 'parser-error',
+        err: 'Failed to parse document',
+      });
+
+      expect(error.message).to.equal('Failed to parse document');
+    });
+
+    it('falls back to err.message for generic Error objects', () => {
+      const inner = new Error('Something went wrong');
+      const error = new ValidationError({
+        type: 'parser-error',
+        err: inner,
+      });
+
+      expect(error.message).to.equal('Something went wrong');
+    });
+
+    it('falls back to a sentinel string when err is undefined', () => {
+      const error = new ValidationError({
+        type: 'parser-error',
+        err: undefined,
+      });
+
+      expect(error.message).to.equal('Unknown parser error');
+    });
+
+    it('falls back to err.title for objects without validationErrors', () => {
+      const error = new ValidationError({
+        type: 'parser-error',
+        err: { title: 'A short title' },
+      });
+
+      expect(error.message).to.equal('A short title');
+    });
+  });
+
+  describe('type: invalid-file', () => {
+    it('renders the file-not-found message and ignores err', () => {
+      const error = new ValidationError({
+        type: 'invalid-file',
+        filepath: '/tmp/missing.yaml',
+        err: { title: 'should not appear' },
+      });
+
+      expect(error.message).to.equal(
+        'There is no file or context with name "/tmp/missing.yaml".',
+      );
+    });
+  });
+
+  describe('type: invalid-syntax-file', () => {
+    it('renders the syntax error template', () => {
+      const error = new ValidationError({
+        type: 'invalid-syntax-file',
+        filepath: '/tmp/bad.yaml',
+      });
+
+      expect(error.message).to.equal('Syntax Error in "/tmp/bad.yaml".');
+    });
+  });
+});