diff --git a/extension/src/shared/__tests__/password-coloring.test.ts b/extension/src/shared/__tests__/password-coloring.test.ts
new file mode 100644
index 0000000..b7421ce
--- /dev/null
+++ b/extension/src/shared/__tests__/password-coloring.test.ts
@@ -0,0 +1,60 @@
+import { describe, it, expect } from 'vitest';
+import { colorizePassword, PWD_DIGIT, PWD_SYMBOL, PWD_LETTER } from '../password-coloring';
+
+describe('colorizePassword', () => {
+
+  function classes(frag: DocumentFragment): string[] {
+    return Array.from(frag.querySelectorAll('span')).map(s => s.className);
+  }
+  function texts(frag: DocumentFragment): string[] {
+    return Array.from(frag.querySelectorAll('span')).map(s => s.textContent ?? '');
+  }
+
+  it('returns empty fragment for empty input', () => {
+    const frag = colorizePassword('');
+    expect(frag.childNodes.length).toBe(0);
+  });
+
+  it('classifies a mixed-class run', () => {
+    const frag = colorizePassword('aB3$xY');
+    expect(classes(frag)).toEqual([PWD_LETTER, PWD_DIGIT, PWD_SYMBOL, PWD_LETTER]);
+    expect(texts(frag)).toEqual(['aB', '3', '$', 'xY']);
+  });
+
+  it('all-letters produces a single letter span', () => {
+    const frag = colorizePassword('passwd');
+    expect(classes(frag)).toEqual([PWD_LETTER]);
+    expect(texts(frag)).toEqual(['passwd']);
+  });
+
+  it('all-digits produces a single digit span', () => {
+    const frag = colorizePassword('123456');
+    expect(classes(frag)).toEqual([PWD_DIGIT]);
+    expect(texts(frag)).toEqual(['123456']);
+  });
+
+  it('all-symbols produces a single symbol span', () => {
+    const frag = colorizePassword('!@#$%^');
+    expect(classes(frag)).toEqual([PWD_SYMBOL]);
+    expect(texts(frag)).toEqual(['!@#$%^']);
+  });
+
+  it('classifies unicode letters as letters', () => {
+    const frag = colorizePassword('áñü');
+    expect(classes(frag)).toEqual([PWD_LETTER]);
+  });
+
+  it('classifies whitespace as symbol', () => {
+    const frag = colorizePassword('a b');
+    expect(classes(frag)).toEqual([PWD_LETTER, PWD_SYMBOL, PWD_LETTER]);
+    expect(texts(frag)).toEqual(['a', ' ', 'b']);
+  });
+
+  it('representative password snapshot: aB3$xY7&_!', () => {
+    const frag = colorizePassword('aB3$xY7&_!');
+    expect(classes(frag)).toEqual([
+      PWD_LETTER, PWD_DIGIT, PWD_SYMBOL, PWD_LETTER, PWD_DIGIT, PWD_SYMBOL,
+    ]);
+    expect(texts(frag)).toEqual(['aB', '3', '$', 'xY', '7', '&_!']);
+  });
+});
diff --git a/extension/src/shared/password-coloring.ts b/extension/src/shared/password-coloring.ts
new file mode 100644
index 0000000..222da85
--- /dev/null
+++ b/extension/src/shared/password-coloring.ts
@@ -0,0 +1,35 @@
+export const PWD_DIGIT = 'pwd-digit';
+export const PWD_SYMBOL = 'pwd-symbol';
+export const PWD_LETTER = 'pwd-letter';
+
+type Class = typeof PWD_DIGIT | typeof PWD_SYMBOL | typeof PWD_LETTER;
+
+function classify(ch: string): Class {
+  if (/^\d$/.test(ch)) return PWD_DIGIT;
+  if (/^\p{L}$/u.test(ch)) return PWD_LETTER;
+  return PWD_SYMBOL;
+}
+
+export function colorizePassword(text: string): DocumentFragment {
+  const frag = document.createDocumentFragment();
+  if (text.length === 0) return frag;
+
+  const codepoints = Array.from(text);
+  let runStart = 0;
+  let runClass = classify(codepoints[0]);
+
+  for (let i = 1; i <= codepoints.length; i++) {
+    const c = i < codepoints.length ? classify(codepoints[i]) : null;
+    if (c !== runClass) {
+      const span = document.createElement('span');
+      span.className = runClass;
+      span.textContent = codepoints.slice(runStart, i).join('');
+      frag.appendChild(span);
+      if (c !== null) {
+        runStart = i;
+        runClass = c;
+      }
+    }
+  }
+  return frag;
+}