diff --git a/package-lock.json b/package-lock.json
index 44b12ec..9d3821a 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -17,7 +17,10 @@
         "@codemirror/view": "^6.35.0",
         "@electron-toolkit/preload": "^3.0.0",
         "@electron-toolkit/utils": "^3.0.0",
+        "@types/dompurify": "^3.0.5",
         "codemirror": "^6.0.1",
+        "dompurify": "^3.3.1",
+        "marked": "^17.0.3",
         "react": "^18.2.0",
         "react-dom": "^18.2.0",
         "zustand": "^4.5.0"
@@ -1986,6 +1989,15 @@
         "@types/ms": "*"
       }
     },
+    "node_modules/@types/dompurify": {
+      "version": "3.0.5",
+      "resolved": "https://registry.npmjs.org/@types/dompurify/-/dompurify-3.0.5.tgz",
+      "integrity": "sha512-1Wg0g3BtQF7sSb27fJQAKck1HECM6zV1EB66j8JH9i3LCjYabJa0FSdiSgsD5K/RbrsR0SiraKacLB+T8ZVYAg==",
+      "license": "MIT",
+      "dependencies": {
+        "@types/trusted-types": "*"
+      }
+    },
     "node_modules/@types/estree": {
       "version": "1.0.8",
       "resolved": "https://registry.npmjs.org/@types/estree/-/estree-1.0.8.tgz",
@@ -2093,6 +2105,12 @@
         "@types/node": "*"
       }
     },
+    "node_modules/@types/trusted-types": {
+      "version": "2.0.7",
+      "resolved": "https://registry.npmjs.org/@types/trusted-types/-/trusted-types-2.0.7.tgz",
+      "integrity": "sha512-ScaPdn1dQczgbl0QFTeTOmVHFULt394XJgOQNoyVhZ6r2vLnMLJfBPd53SB52T/3G36VI1/g2MZaX0cwDuXsfw==",
+      "license": "MIT"
+    },
     "node_modules/@types/verror": {
       "version": "1.10.11",
       "resolved": "https://registry.npmjs.org/@types/verror/-/verror-1.10.11.tgz",
@@ -3356,6 +3374,15 @@
         "node": ">=8"
       }
     },
+    "node_modules/dompurify": {
+      "version": "3.3.1",
+      "resolved": "https://registry.npmjs.org/dompurify/-/dompurify-3.3.1.tgz",
+      "integrity": "sha512-qkdCKzLNtrgPFP1Vo+98FRzJnBRGe4ffyCea9IwHB1fyxPOeNTHpLKYGd4Uk9xvNoH0ZoOjwZxNptyMwqrId1Q==",
+      "license": "(MPL-2.0 OR Apache-2.0)",
+      "optionalDependencies": {
+        "@types/trusted-types": "^2.0.7"
+      }
+    },
     "node_modules/dotenv": {
       "version": "9.0.2",
       "resolved": "https://registry.npmjs.org/dotenv/-/dotenv-9.0.2.tgz",
@@ -4741,6 +4768,18 @@
         "@jridgewell/sourcemap-codec": "^1.5.5"
       }
     },
+    "node_modules/marked": {
+      "version": "17.0.3",
+      "resolved": "https://registry.npmjs.org/marked/-/marked-17.0.3.tgz",
+      "integrity": "sha512-jt1v2ObpyOKR8p4XaUJVk3YWRJ5n+i4+rjQopxvV32rSndTJXvIzuUdWWIy/1pFQMkQmvTXawzDNqOH/CUmx6A==",
+      "license": "MIT",
+      "bin": {
+        "marked": "bin/marked.js"
+      },
+      "engines": {
+        "node": ">= 20"
+      }
+    },
     "node_modules/matcher": {
       "version": "3.0.0",
       "resolved": "https://registry.npmjs.org/matcher/-/matcher-3.0.0.tgz",
diff --git a/package.json b/package.json
index acb26c4..390e604 100644
--- a/package.json
+++ b/package.json
@@ -31,7 +31,10 @@
     "@codemirror/view": "^6.35.0",
     "@electron-toolkit/preload": "^3.0.0",
     "@electron-toolkit/utils": "^3.0.0",
+    "@types/dompurify": "^3.0.5",
     "codemirror": "^6.0.1",
+    "dompurify": "^3.3.1",
+    "marked": "^17.0.3",
     "react": "^18.2.0",
     "react-dom": "^18.2.0",
     "zustand": "^4.5.0"
diff --git a/src/renderer/components/AIChat/Chat.css b/src/renderer/components/AIChat/Chat.css
index 3d72ac2..6f3d319 100644
--- a/src/renderer/components/AIChat/Chat.css
+++ b/src/renderer/components/AIChat/Chat.css
@@ -85,6 +85,88 @@
   padding: 10px 12px;
 }
 
+/* Assistant messages use rendered Markdown — no pre-wrap needed */
+.chat-message-assistant .chat-message-content {
+  white-space: normal;
+}
+
+.chat-message-markdown {
+  word-break: break-word;
+}
+
+.chat-message-markdown p {
+  margin: 0 0 14px;
+}
+.chat-message-markdown p:last-child {
+  margin-bottom: 0;
+}
+
+.chat-message-markdown h1,
+.chat-message-markdown h2,
+.chat-message-markdown h3 {
+  color: var(--heading-color);
+  font-family: var(--font-serif);
+  font-weight: 600;
+  margin: 12px 0 4px;
+  line-height: 1.3;
+}
+.chat-message-markdown h1 { font-size: 15px; }
+.chat-message-markdown h2 { font-size: 14px; }
+.chat-message-markdown h3 { font-size: 13px; }
+
+.chat-message-markdown ul,
+.chat-message-markdown ol {
+  margin: 4px 0 8px;
+  padding-left: 18px;
+}
+.chat-message-markdown li {
+  margin-bottom: 3px;
+}
+
+.chat-message-markdown code {
+  font-family: monospace;
+  font-size: 12px;
+  background: rgba(255, 255, 255, 0.07);
+  border-radius: 3px;
+  padding: 1px 4px;
+}
+
+.chat-message-markdown pre {
+  background: rgba(0, 0, 0, 0.3);
+  border-radius: 5px;
+  padding: 10px 12px;
+  overflow-x: auto;
+  margin: 6px 0;
+}
+.chat-message-markdown pre code {
+  background: none;
+  padding: 0;
+  font-size: 12px;
+}
+
+.chat-message-markdown blockquote {
+  border-left: 3px solid var(--accent);
+  margin: 6px 0;
+  padding: 2px 10px;
+  color: var(--text-secondary);
+  font-style: italic;
+}
+
+.chat-message-markdown strong {
+  color: var(--text-primary);
+  font-weight: 600;
+}
+
+.chat-message-markdown em {
+  color: var(--text-secondary);
+}
+
+.chat-message-markdown hr {
+  border: none;
+  border-top: 1px solid var(--border);
+  margin: 10px 0;
+}
+
 .chat-message-user .chat-message-content {
   background: var(--user-message-bg);
 }
diff --git a/src/renderer/components/AIChat/ChatMessageItem.tsx b/src/renderer/components/AIChat/ChatMessageItem.tsx
index 24c83f7..f535915 100644
--- a/src/renderer/components/AIChat/ChatMessageItem.tsx
+++ b/src/renderer/components/AIChat/ChatMessageItem.tsx
@@ -1,17 +1,35 @@
+import { useMemo } from 'react'
+import { marked } from 'marked'
+import DOMPurify from 'dompurify'
 import type { ChatMessage } from '../../types/editor'
 
+marked.setOptions({ breaks: true })
+
 interface Props {
   message: ChatMessage
 }
 
 export function ChatMessageItem({ message }: Props): JSX.Element {
+  const html = useMemo(() => {
+    if (message.role !== 'assistant' || !message.content) return null
+    const raw = marked.parse(message.content) as string
+    return DOMPurify.sanitize(raw)
+  }, [message.role, message.content])
+
   return (
     <div className={`chat-message chat-message-${message.role}`}>
       <div className="chat-message-label">
         {message.role === 'user' ? 'You' : 'Editor AI'}
       </div>
       <div className="chat-message-content">
-        {message.content || <span className="chat-streaming-cursor">▍</span>}
+        {html ? (
+          <div
+            className="chat-message-markdown"
+            dangerouslySetInnerHTML={{ __html: html }}
+          />
+        ) : (
+          message.content || <span className="chat-streaming-cursor">▍</span>
+        )}
       </div>
     </div>
   )
diff --git a/src/renderer/components/Editor/MarkdownEditor.tsx b/src/renderer/components/Editor/MarkdownEditor.tsx
index b3a470e..c1a0c47 100644
--- a/src/renderer/components/Editor/MarkdownEditor.tsx
+++ b/src/renderer/components/Editor/MarkdownEditor.tsx
@@ -1,6 +1,6 @@
 import { useEffect, useRef } from 'react'
 import { EditorView, Decoration, type DecorationSet } from '@codemirror/view'
-import { EditorState, StateField, StateEffect, RangeSetBuilder } from '@codemirror/state'
+import { EditorState, StateField, StateEffect, RangeSetBuilder, Compartment } from '@codemirror/state'
 import { markdown } from '@codemirror/lang-markdown'
 import { syntaxHighlighting, defaultHighlightStyle } from '@codemirror/language'
 import { history, defaultKeymap, historyKeymap } from '@codemirror/commands'
@@ -44,12 +44,14 @@ const annotationField = StateField.define<DecorationSet>({
   provide: (f) => EditorView.decorations.from(f)
 })
 
-// Dark gothic theme for CodeMirror
-const hohoffTheme = EditorView.theme(
+const themeCompartment = new Compartment()
+
+function buildTheme(fontSize: number): ReturnType<typeof EditorView.theme> {
+  return EditorView.theme(
   {
     '&': {
       height: '100%',
-      fontSize: '15px',
+      fontSize: `${fontSize}px`,
       backgroundColor: 'transparent',
       color: 'var(--text-primary)'
     },
@@ -59,7 +61,7 @@ const hohoffTheme = EditorView.theme(
       overflow: 'auto'
     },
     '.cm-content': {
-      padding: '24px 32px',
+      padding: '16px 20px',
       maxWidth: '740px',
       margin: '0 auto',
       caretColor: 'var(--accent)'
@@ -67,7 +69,7 @@ const hohoffTheme = EditorView.theme(
     '.cm-cursor': { borderLeftColor: 'var(--accent)' },
     '.cm-selectionBackground': { backgroundColor: 'rgba(167,139,95,0.2)' },
     '&.cm-focused .cm-selectionBackground': { backgroundColor: 'rgba(167,139,95,0.3)' },
-    '.cm-line': { padding: '0' },
+    '.cm-line': { padding: '0', marginBottom: '6px' },
     '.cm-gutters': { display: 'none' },
     '.cm-activeLine': { backgroundColor: 'transparent' },
     '.cm-activeLineGutter': { backgroundColor: 'transparent' },
@@ -97,12 +99,13 @@ const hohoffTheme = EditorView.theme(
     }
   },
   { dark: true }
-)
+  )
+}
 
 export function MarkdownEditor(): JSX.Element {
   const containerRef = useRef<HTMLDivElement>(null)
   const viewRef = useRef<EditorView | null>(null)
-  const { activeFilePath, activeFileContent, setContent, annotations } = useEditorStore()
+  const { activeFilePath, activeFileContent, setContent, annotations, fontSize } = useEditorStore()
 
   // Initialize CodeMirror once
   useEffect(() => {
@@ -117,7 +120,7 @@ export function MarkdownEditor(): JSX.Element {
           markdown(),
           syntaxHighlighting(defaultHighlightStyle),
           annotationField,
-          hohoffTheme,
+          themeCompartment.of(buildTheme(fontSize)),
           EditorView.lineWrapping,
           EditorView.updateListener.of((update) => {
             if (update.docChanged) {
@@ -158,6 +161,13 @@ export function MarkdownEditor(): JSX.Element {
     view.dispatch({ effects: setAnnotationsEffect.of(annotations) })
   }, [annotations])
 
+  // Reconfigure theme when font size changes
+  useEffect(() => {
+    const view = viewRef.current
+    if (!view) return
+    view.dispatch({ effects: themeCompartment.reconfigure(buildTheme(fontSize)) })
+  }, [fontSize])
+
   return (
     <div className="editor-container">
       {!activeFilePath && (
diff --git a/src/renderer/components/Toolbar/AnalysisToolbar.tsx b/src/renderer/components/Toolbar/AnalysisToolbar.tsx
index b5e83a0..fd0ed3a 100644
--- a/src/renderer/components/Toolbar/AnalysisToolbar.tsx
+++ b/src/renderer/components/Toolbar/AnalysisToolbar.tsx
@@ -31,7 +31,9 @@ export function AnalysisToolbar(): JSX.Element {
     setAIError,
     chatHistory,
     projectWordCount,
-    setProjectWordCount
+    setProjectWordCount,
+    fontSize,
+    setFontSize
   } = useEditorStore()
 
   useEffect(() => {
@@ -154,6 +156,24 @@ export function AnalysisToolbar(): JSX.Element {
       </div>
 
       <div className="toolbar-right">
+        <div className="toolbar-fontsize">
+          <button
+            className="toolbar-fontsize-btn"
+            onClick={() => setFontSize(fontSize - 1)}
+            disabled={fontSize <= 11}
+            title="Decrease font size"
+          >
+            A−
+          </button>
+          <button
+            className="toolbar-fontsize-btn"
+            onClick={() => setFontSize(fontSize + 1)}
+            disabled={fontSize >= 24}
+            title="Increase font size"
+          >
+            A+
+          </button>
+        </div>
         {activeFilePath && (
           <span
             className="toolbar-wordcount"
diff --git a/src/renderer/components/Toolbar/Toolbar.css b/src/renderer/components/Toolbar/Toolbar.css
index 03ce930..b30e4d5 100644
--- a/src/renderer/components/Toolbar/Toolbar.css
+++ b/src/renderer/components/Toolbar/Toolbar.css
@@ -96,6 +96,37 @@
   max-width: 260px;
 }
 
+.toolbar-fontsize {
+  display: flex;
+  align-items: center;
+  gap: 2px;
+  flex-shrink: 0;
+}
+
+.toolbar-fontsize-btn {
+  background: none;
+  border: 1px solid var(--border);
+  border-radius: 4px;
+  color: var(--text-muted);
+  font-size: 11px;
+  font-family: var(--font-sans);
+  padding: 2px 6px;
+  cursor: pointer;
+  transition: color 0.15s, border-color 0.15s;
+  white-space: nowrap;
+  line-height: 1.4;
+}
+
+.toolbar-fontsize-btn:hover:not(:disabled) {
+  color: var(--text-primary);
+  border-color: var(--text-muted);
+}
+
+.toolbar-fontsize-btn:disabled {
+  opacity: 0.3;
+  cursor: default;
+}
+
 .toolbar-wordcount {
   color: var(--text-muted);
   font-size: 11px;
diff --git a/src/renderer/store/editorStore.ts b/src/renderer/store/editorStore.ts
index 6b05811..4c1735a 100644
--- a/src/renderer/store/editorStore.ts
+++ b/src/renderer/store/editorStore.ts
@@ -38,6 +38,10 @@ interface EditorState {
   // Word counts
   projectWordCount: number
   setProjectWordCount: (count: number) => void
+
+  // Editor font size
+  fontSize: number
+  setFontSize: (size: number) => void
 }
 
 export const useEditorStore = create<EditorState>((set, get) => ({
@@ -122,5 +126,12 @@ export const useEditorStore = create<EditorState>((set, get) => ({
   setAnalysisMode: (analysisMode) => set({ analysisMode }),
 
   projectWordCount: 0,
-  setProjectWordCount: (projectWordCount) => set({ projectWordCount })
+  setProjectWordCount: (projectWordCount) => set({ projectWordCount }),
+
+  fontSize: Number(localStorage.getItem('editorFontSize')) || 15,
+  setFontSize: (size) => {
+    const clamped = Math.max(11, Math.min(24, size))
+    localStorage.setItem('editorFontSize', String(clamped))
+    set({ fontSize: clamped })
+  }
 }))