diff --git a/src/constants.ts b/src/constants.ts
index 0e0e67e..8cb43b9 100644
--- a/src/constants.ts
+++ b/src/constants.ts
@@ -1,8 +1,3 @@
-export const ERROR_NO_CONTENT = 'content variable is empty';
-export const ERROR_TYPE_NOT_STRING = 'content variable is not a string';
-
+/** Status strings that are not MarkupGeneratorError codes. */
 export const HTML_EMAIL_SUCCESS = 'Content has correct html!!!';
 export const HTML_EMAIL_ERROR = 'Content has not correct html!!!';
-
-export const CONST_FILE_CREATED = '';
-export const CONST_FILE_NOT_WRITTEN = 'file not written';
diff --git a/src/errors.ts b/src/errors.ts
index c40f4b3..f6e1047 100644
--- a/src/errors.ts
+++ b/src/errors.ts
@@ -8,10 +8,24 @@ export type MarkupGeneratorErrorCode =
   | 'EIMPORT'
   | 'EREAD';
 
+export const DEFAULT_MESSAGES: Record<MarkupGeneratorErrorCode, string> = {
+  EMPTY_CONTENT: 'content variable is empty',
+  NOT_A_STRING: 'content variable is not a string',
+  FILE_EXISTS: 'file already exists',
+  WRITE_FAILED: 'file not written',
+  JSON_READ: 'failed to read JSON file',
+  JSON_PARSE: 'failed to parse JSON file',
+  EIMPORT: 'failed to import module',
+  EREAD: 'failed to read path',
+};
+
 export class MarkupGeneratorError extends Error {
   readonly code: MarkupGeneratorErrorCode;
 
-  constructor(code: MarkupGeneratorErrorCode, message: string) {
+  constructor(
+    code: MarkupGeneratorErrorCode,
+    message: string = DEFAULT_MESSAGES[code]
+  ) {
     super(message);
     this.name = 'MarkupGeneratorError';
     this.code = code;
diff --git a/src/index.ts b/src/index.ts
index cf26960..94d4c37 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -40,7 +40,7 @@ export type {
   RenderOptions,
   WriteOptions,
 } from './templateGenerator';
-export { MarkupGeneratorError } from './errors';
+export { MarkupGeneratorError, DEFAULT_MESSAGES } from './errors';
 export type { MarkupGeneratorErrorCode } from './errors';
 
 export {
diff --git a/src/write.ts b/src/write.ts
index 4bc7a05..15d0881 100644
--- a/src/write.ts
+++ b/src/write.ts
@@ -15,6 +15,7 @@ import type { WriteGeneratedFileOptions } from './types';
  * - existing files are overwritten unless a caller uses writeGeneratedFile({ overwrite: 'error' })
  * - empty content throws EMPTY_CONTENT
  * - non-string content throws NOT_A_STRING
+ * - write failures throw WRITE_FAILED (default message from DEFAULT_MESSAGES)
  */
 const writeHTML = async (
   fileName: string,
@@ -23,14 +24,11 @@ const writeHTML = async (
   message: string = ''
 ): Promise<void> => {
   if (!data) {
-    throw new MarkupGeneratorError('EMPTY_CONTENT', 'content variable is empty');
+    throw new MarkupGeneratorError('EMPTY_CONTENT');
   }
 
   if (typeof data !== 'string') {
-    throw new MarkupGeneratorError(
-      'NOT_A_STRING',
-      'content variable is not a string'
-    );
+    throw new MarkupGeneratorError('NOT_A_STRING');
   }
 
   if (dir === '') {
@@ -46,7 +44,7 @@ const writeHTML = async (
       console.log(message);
     }
   } catch {
-    throw new MarkupGeneratorError('WRITE_FAILED', 'file not written');
+    throw new MarkupGeneratorError('WRITE_FAILED');
   }
 };
 
@@ -63,6 +61,10 @@ const writingFile = async (content: string, name: string = 'prefix'): Promise<vo
   await writeHTML(generateFileName(name), content);
 };
 
+/**
+ * Preferred writer. Returns the absolute path that was written.
+ * Default overwrite policy is replace. Use overwrite: 'error' to throw FILE_EXISTS.
+ */
 const writeGeneratedFile = async (
   options: WriteGeneratedFileOptions
 ): Promise<string> => {
diff --git a/tests/default-messages.test.ts b/tests/default-messages.test.ts
new file mode 100644
index 0000000..2298b92
--- /dev/null
+++ b/tests/default-messages.test.ts
@@ -0,0 +1,22 @@
+import { describe, expect, test } from 'vitest';
+import { DEFAULT_MESSAGES, MarkupGeneratorError } from '../src/index';
+
+describe('DEFAULT_MESSAGES', () => {
+  test('every code has a default message', () => {
+    expect(new MarkupGeneratorError('EMPTY_CONTENT').message).toBe(
+      DEFAULT_MESSAGES.EMPTY_CONTENT
+    );
+    expect(new MarkupGeneratorError('WRITE_FAILED').message).toBe(
+      DEFAULT_MESSAGES.WRITE_FAILED
+    );
+    expect(new MarkupGeneratorError('FILE_EXISTS').message).toBe(
+      DEFAULT_MESSAGES.FILE_EXISTS
+    );
+  });
+
+  test('explicit message still wins', () => {
+    expect(new MarkupGeneratorError('FILE_EXISTS', 'custom').message).toBe(
+      'custom'
+    );
+  });
+});
diff --git a/tests/index.test.ts b/tests/index.test.ts
index 505851c..1ee8d53 100644
--- a/tests/index.test.ts
+++ b/tests/index.test.ts
@@ -7,8 +7,8 @@ import {
   readSourceFile,
   writeHTML,
   writingFile,
+  DEFAULT_MESSAGES,
 } from '../src/index';
-import { ERROR_NO_CONTENT, ERROR_TYPE_NOT_STRING } from '../src/constants';
 
 const UUID_RE = '[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}';
 
@@ -50,14 +50,14 @@ describe('writeHTML', () => {
 
   test('throws when content is empty', async () => {
     await expect(writeHTML('empty.html', '', outDir)).rejects.toThrow(
-      ERROR_NO_CONTENT
+      DEFAULT_MESSAGES.EMPTY_CONTENT
     );
   });
 
   test('throws when content is not a string', async () => {
     await expect(
       writeHTML('bad.html', 123 as unknown as string, outDir)
-    ).rejects.toThrow(ERROR_TYPE_NOT_STRING);
+    ).rejects.toThrow(DEFAULT_MESSAGES.NOT_A_STRING);
   });
 });