diff --git a/src/components/diff-viewer.tsx b/src/components/diff-viewer.tsx
index baba1be9..2aa4b2e7 100644
--- a/src/components/diff-viewer.tsx
+++ b/src/components/diff-viewer.tsx
@@ -1,56 +1,102 @@
-import { createMemo } from "solid-js"
-import type { TextPart } from "../types/message"
-import { Markdown } from "./markdown"
+import { createMemo, Show, onMount, createEffect } from "solid-js"
+import { DiffView, DiffModeEnum } from "@git-diff-view/solid"
+import { getLanguageFromPath } from "../lib/markdown"
 import { normalizeDiffText } from "../lib/diff-utils"
-import { getToolRenderCache, setToolRenderCache } from "../lib/tool-render-cache"
-
-type ThemeKey = "light" | "dark"
+import { setToolRenderCache } from "../lib/tool-render-cache"
+import type { DiffViewMode } from "../stores/preferences"
 
 interface ToolCallDiffViewerProps {
   diffText: string
   filePath?: string
-  theme: ThemeKey
-  renderCacheKey?: string
+  theme: "light" | "dark"
+  mode: DiffViewMode
+  onRendered?: () => void
+  cachedHtml?: string
+  cacheKey?: string
 }
 
-
-function formatDiffMarkdown(diffText: string, filePath?: string): string {
-  const body = normalizeDiffText(diffText) || diffText
-  const trimmed = body.trimStart()
-  const alreadyFenced = trimmed.startsWith("```")
-  const fenced = alreadyFenced ? body : `\`\`\`diff\n${body}\n\`\`\``
-
-  if (!filePath) {
-    return fenced
-  }
-  return `### ${filePath}\n\n${fenced}`
+type DiffData = {
+  oldFile?: { fileName?: string | null; fileLang?: string | null; content?: string | null }
+  newFile?: { fileName?: string | null; fileLang?: string | null; content?: string | null }
+  hunks: string[]
 }
 
 export function ToolCallDiffViewer(props: ToolCallDiffViewerProps) {
-  const diffMarkdown = createMemo(() => {
-    return formatDiffMarkdown(props.diffText, props.filePath)
+  const diffData = createMemo<DiffData | null>(() => {
+    const normalized = normalizeDiffText(props.diffText)
+    if (!normalized) {
+      return null
+    }
+
+    const language = getLanguageFromPath(props.filePath) || "text"
+    const fileName = props.filePath || "diff"
+
+    return {
+      oldFile: {
+        fileName,
+        fileLang: language as any, // Cast to any to avoid type issues with DiffHighlighterLang
+      },
+      newFile: {
+        fileName,
+        fileLang: language as any, // Cast to any to avoid type issues with DiffHighlighterLang
+      },
+      hunks: [normalized],
+    }
   })
 
-  const diffPart = createMemo<TextPart>(() => {
-    const part: TextPart = { type: "text", text: diffMarkdown() }
-    if (props.renderCacheKey) {
-      const cached = getToolRenderCache(props.renderCacheKey)
-      if (cached) {
-        part.renderCache = cached
+  let diffContainerRef: HTMLDivElement | undefined
+
+  const captureAndCacheHtml = () => {
+    if (diffContainerRef && props.cacheKey && !props.cachedHtml) {
+      // Extract the rendered HTML from DiffView container
+      const renderedHtml = diffContainerRef.innerHTML
+      if (renderedHtml) {
+        setToolRenderCache(props.cacheKey, {
+          text: props.diffText,
+          html: renderedHtml,
+          theme: props.theme,
+          mode: props.mode,
+        })
       }
     }
-    return part
-  })
-
-  const handleRendered = () => {
-    if (!props.renderCacheKey) return
-    setToolRenderCache(props.renderCacheKey, diffPart().renderCache)
+    props.onRendered?.()
   }
 
+  // Also capture HTML when diff data changes
+  createEffect(() => {
+    const data = diffData()
+    if (data && !props.cachedHtml) {
+      // Delay to allow DiffView to re-render with new data
+      setTimeout(captureAndCacheHtml, 100)
+    }
+  })
+
   return (
     <div class="tool-call-diff-viewer">
-      <Markdown part={diffPart()} isDark={props.theme === "dark"} onRendered={handleRendered} />
+      <Show
+        when={props.cachedHtml}
+        fallback={
+          <div ref={diffContainerRef}>
+            <Show
+              when={diffData()}
+              fallback={<pre class="tool-call-diff-fallback">{props.diffText}</pre>}
+            >
+              {(data) => (
+                <DiffView
+                  data={data()}
+                  diffViewMode={props.mode === "split" ? DiffModeEnum.Split : DiffModeEnum.Unified}
+                  diffViewTheme={props.theme}
+                  diffViewHighlight
+                  diffViewWrap={false}
+                  diffViewFontSize={13}
+                />
+              )}
+            </Show>
+          </div>
+        }
+      >
+        <div innerHTML={props.cachedHtml} />
+      </Show>
     </div>
   )
-}
-
+}
\ No newline at end of file
diff --git a/src/components/tool-call.tsx b/src/components/tool-call.tsx
index 38c19f64..cca0f6e4 100644
--- a/src/components/tool-call.tsx
+++ b/src/components/tool-call.tsx
@@ -6,6 +6,7 @@ import { useTheme } from "../lib/theme"
 import { getLanguageFromPath } from "../lib/markdown"
 import { isRenderableDiffText } from "../lib/diff-utils"
 import { getToolRenderCache, setToolRenderCache } from "../lib/tool-render-cache"
+import { preferences, setDiffViewMode, type DiffViewMode } from "../stores/preferences"
 import type { TextPart } from "../types/message"
 
 
@@ -385,6 +386,33 @@ export default function ToolCall(props: ToolCallProps) {
     const relativePath = payload.filePath ? getRelativePath(payload.filePath) : ""
     const toolbarLabel = relativePath ? `Diff · ${relativePath}` : "Diff"
     const cacheKey = makeRenderCacheKey(toolCallId(), props.messageId, props.messageVersion, props.partVersion)
+    const diffMode = () => (preferences().diffViewMode || "split") as DiffViewMode
+    const themeKey = isDark() ? "dark" : "light"
+
+    // Check if we have valid cache
+    let cachedHtml: string | undefined
+    if (cacheKey) {
+      const cached = getToolRenderCache(cacheKey)
+      const currentMode = diffMode()
+      if (cached && 
+          cached.text === payload.diffText && 
+          cached.theme === themeKey &&
+          cached.mode === currentMode) {
+        cachedHtml = cached.html
+      }
+    }
+
+    const handleModeChange = (mode: DiffViewMode) => {
+      setDiffViewMode(mode)
+    }
+
+    const handleDiffRendered = () => {
+      if (cacheKey && !cachedHtml) {
+        // Cache will be updated by the diff viewer component itself
+        // We'll capture HTML from the rendered component
+      }
+      handleScrollRendered()
+    }
 
     return (
       <div
@@ -392,14 +420,35 @@ export default function ToolCall(props: ToolCallProps) {
         ref={(element) => initializeScrollContainer(element)}
         onScroll={(event) => updateScrollState(toolCallId(), event.currentTarget)}
       >
-        <div class="tool-call-diff-toolbar">
+        <div class="tool-call-diff-toolbar" role="group" aria-label="Diff view mode">
           <span class="tool-call-diff-toolbar-label">{toolbarLabel}</span>
+          <div class="tool-call-diff-toggle">
+            <button
+              type="button"
+              class={`tool-call-diff-mode-button${diffMode() === "split" ? " active" : ""}`}
+              aria-pressed={diffMode() === "split"}
+              onClick={() => handleModeChange("split")}
+            >
+              Split
+            </button>
+            <button
+              type="button"
+              class={`tool-call-diff-mode-button${diffMode() === "unified" ? " active" : ""}`}
+              aria-pressed={diffMode() === "unified"}
+              onClick={() => handleModeChange("unified")}
+            >
+              Unified
+            </button>
+          </div>
         </div>
         <ToolCallDiffViewer
           diffText={payload.diffText}
           filePath={payload.filePath}
-          theme={isDark() ? "dark" : "light"}
-          renderCacheKey={cacheKey}
+          theme={themeKey}
+          mode={diffMode()}
+          cachedHtml={cachedHtml}
+          cacheKey={cacheKey}
+          onRendered={handleDiffRendered}
         />
       </div>
     )
diff --git a/src/types/message.ts b/src/types/message.ts
index ff686fa8..ec442c86 100644
--- a/src/types/message.ts
+++ b/src/types/message.ts
@@ -2,6 +2,7 @@ export interface RenderCache {
   text: string
   html: string
   theme?: string
+  mode?: string
 }
 
 export interface MessageDisplayParts {