diff --git a/src/components/code-block-inline.tsx b/src/components/code-block-inline.tsx
new file mode 100644
index 00000000..51d144db
--- /dev/null
+++ b/src/components/code-block-inline.tsx
@@ -0,0 +1,129 @@
+import { createSignal, onMount, Show } from "solid-js"
+import { getHighlighter, type Highlighter } from "shiki"
+import { useTheme } from "../lib/theme"
+
+interface CodeBlockInlineProps {
+  code: string
+  language?: string
+}
+
+let highlighter: Highlighter | null = null
+
+async function getOrCreateHighlighter() {
+  if (!highlighter) {
+    highlighter = await getHighlighter({
+      themes: ["github-light", "github-dark"],
+      langs: [
+        "typescript",
+        "javascript",
+        "python",
+        "bash",
+        "json",
+        "html",
+        "css",
+        "markdown",
+        "yaml",
+        "sql",
+        "rust",
+        "go",
+        "cpp",
+        "c",
+        "java",
+        "csharp",
+        "php",
+        "ruby",
+        "swift",
+        "kotlin",
+        "diff",
+        "shell",
+      ],
+    })
+  }
+  return highlighter
+}
+
+export function CodeBlockInline(props: CodeBlockInlineProps) {
+  const { isDark } = useTheme()
+  const [html, setHtml] = createSignal("")
+  const [copied, setCopied] = createSignal(false)
+  const [ready, setReady] = createSignal(false)
+
+  onMount(async () => {
+    const hl = await getOrCreateHighlighter()
+    setReady(true)
+    updateHighlight(hl)
+  })
+
+  const updateHighlight = async (hl: Highlighter) => {
+    if (!props.language) {
+      setHtml(`<pre><code>${escapeHtml(props.code)}</code></pre>`)
+      return
+    }
+
+    try {
+      const highlighted = hl.codeToHtml(props.code, {
+        lang: props.language,
+        theme: isDark() ? "github-dark" : "github-light",
+      })
+      setHtml(highlighted)
+    } catch {
+      setHtml(`<pre><code>${escapeHtml(props.code)}</code></pre>`)
+    }
+  }
+
+  const copyCode = async () => {
+    await navigator.clipboard.writeText(props.code)
+    setCopied(true)
+    setTimeout(() => setCopied(false), 2000)
+  }
+
+  return (
+    <Show
+      when={ready()}
+      fallback={
+        <pre class="tool-call-content">
+          <code>{props.code}</code>
+        </pre>
+      }
+    >
+      <div class="code-block-inline">
+        <div class="code-block-header">
+          <Show when={props.language}>
+            <span class="code-block-language">{props.language}</span>
+          </Show>
+          <button onClick={copyCode} class="code-block-copy">
+            <svg
+              class="copy-icon"
+              width="16"
+              height="16"
+              viewBox="0 0 24 24"
+              fill="none"
+              stroke="currentColor"
+              stroke-width="2"
+            >
+              <rect x="9" y="9" width="13" height="13" rx="2" ry="2"></rect>
+              <path d="M5 15H4a2 2 0 0 1-2-2V4a2 2 0 0 1 2-2h9a2 2 0 0 1 2 2v1"></path>
+            </svg>
+            <span class="copy-text">
+              <Show when={copied()} fallback="Copy">
+                Copied!
+              </Show>
+            </span>
+          </button>
+        </div>
+        <div innerHTML={html()} />
+      </div>
+    </Show>
+  )
+}
+
+function escapeHtml(text: string): string {
+  const map: Record<string, string> = {
+    "&": "&amp;",
+    "<": "&lt;",
+    ">": "&gt;",
+    '"': "&quot;",
+    "'": "&#039;",
+  }
+  return text.replace(/[&<>"']/g, (m) => map[m])
+}
diff --git a/src/components/markdown.tsx b/src/components/markdown.tsx
new file mode 100644
index 00000000..450e0b10
--- /dev/null
+++ b/src/components/markdown.tsx
@@ -0,0 +1,95 @@
+import { createEffect, createSignal, onMount, Show } from "solid-js"
+import { initMarkdown, renderMarkdown } from "../lib/markdown"
+
+interface MarkdownProps {
+  content: string
+  isDark?: boolean
+}
+
+export function Markdown(props: MarkdownProps) {
+  const [html, setHtml] = createSignal("")
+  const [ready, setReady] = createSignal(false)
+  let containerRef: HTMLDivElement | undefined
+
+  onMount(async () => {
+    await initMarkdown(props.isDark ?? false)
+    setReady(true)
+  })
+
+  createEffect(async () => {
+    if (ready()) {
+      const rendered = await renderMarkdown(props.content)
+      setHtml(rendered)
+    }
+  })
+
+  createEffect(async () => {
+    if (props.isDark !== undefined) {
+      await initMarkdown(props.isDark)
+      if (ready()) {
+        const rendered = await renderMarkdown(props.content)
+        setHtml(rendered)
+      }
+    }
+  })
+
+  createEffect(() => {
+    const currentHtml = html()
+    if (containerRef && currentHtml) {
+      setTimeout(() => {
+        const codeBlocks = containerRef?.querySelectorAll(".markdown-code-block")
+
+        codeBlocks?.forEach((block) => {
+          const existing = block.querySelector(".code-block-header")
+          if (existing) return
+
+          const lang = block.getAttribute("data-language")
+          const encodedCode = block.getAttribute("data-code")
+
+          const header = document.createElement("div")
+          header.className = "code-block-header"
+
+          const languageSpan = lang
+            ? `<span class="code-block-language">${lang}</span>`
+            : '<span class="code-block-language"></span>'
+
+          header.innerHTML = `
+          ${languageSpan}
+          <button class="code-block-copy" data-code="${encodedCode || ""}">
+            <svg class="copy-icon" width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2">
+              <rect x="9" y="9" width="13" height="13" rx="2" ry="2"></rect>
+              <path d="M5 15H4a2 2 0 0 1-2-2V4a2 2 0 0 1 2-2h9a2 2 0 0 1 2 2v1"></path>
+            </svg>
+            <span class="copy-text">Copy</span>
+          </button>
+        `
+          block.insertBefore(header, block.firstChild)
+
+          const button = header.querySelector(".code-block-copy")
+          if (button) {
+            button.addEventListener("click", async () => {
+              const code = button.getAttribute("data-code")
+              if (code) {
+                const decodedCode = decodeURIComponent(code)
+                await navigator.clipboard.writeText(decodedCode)
+                const copyText = button.querySelector(".copy-text")
+                if (copyText) {
+                  copyText.textContent = "Copied!"
+                  setTimeout(() => {
+                    copyText.textContent = "Copy"
+                  }, 2000)
+                }
+              }
+            })
+          }
+        })
+      }, 0)
+    }
+  })
+
+  return (
+    <Show when={ready()} fallback={<div class="text-gray-500">Loading...</div>}>
+      <div ref={containerRef} class="prose prose-sm dark:prose-invert max-w-none" innerHTML={html()} />
+    </Show>
+  )
+}
diff --git a/src/components/message-part.tsx b/src/components/message-part.tsx
index 303b949d..b59a2822 100644
--- a/src/components/message-part.tsx
+++ b/src/components/message-part.tsx
@@ -1,12 +1,15 @@
 import { Show, Match, Switch } from "solid-js"
 import ToolCall from "./tool-call"
 import { isItemExpanded, toggleItemExpanded } from "../stores/tool-call-state"
+import { Markdown } from "./markdown"
+import { useTheme } from "../lib/theme"
 
 interface MessagePartProps {
   part: any
 }
 
 export default function MessagePart(props: MessagePartProps) {
+  const { isDark } = useTheme()
   const partType = () => props.part?.type || ""
   const reasoningId = () => `reasoning-${props.part?.id || ""}`
   const isReasoningExpanded = () => isItemExpanded(reasoningId())
@@ -20,7 +23,9 @@ export default function MessagePart(props: MessagePartProps) {
     <Switch>
       <Match when={partType() === "text"}>
         <Show when={!props.part.synthetic && props.part.text}>
-          <div class="message-text">{props.part.text}</div>
+          <div class="message-text">
+            <Markdown content={props.part.text} isDark={isDark()} />
+          </div>
         </Show>
       </Match>
 
@@ -40,7 +45,9 @@ export default function MessagePart(props: MessagePartProps) {
               <span class="reasoning-label">Reasoning</span>
             </div>
             <Show when={isReasoningExpanded()}>
-              <div class="message-text mt-2">{props.part.text || ""}</div>
+              <div class="message-text mt-2">
+                <Markdown content={props.part.text || ""} isDark={isDark()} />
+              </div>
             </Show>
           </div>
         </div>
diff --git a/src/components/tool-call.tsx b/src/components/tool-call.tsx
index 7237918e..fa250e80 100644
--- a/src/components/tool-call.tsx
+++ b/src/components/tool-call.tsx
@@ -1,5 +1,6 @@
 import { createSignal, Show, For, createEffect } from "solid-js"
 import { isToolCallExpanded, toggleToolCallExpanded } from "../stores/tool-call-state"
+import { CodeBlockInline } from "./code-block-inline"
 
 interface ToolCallProps {
   toolCall: any
@@ -59,6 +60,42 @@ function getRelativePath(path: string): string {
   return parts.slice(-1)[0] || path
 }
 
+function getLanguageFromPath(path: string): string | undefined {
+  if (!path) return undefined
+  const ext = path.split(".").pop()?.toLowerCase()
+  const langMap: Record<string, string> = {
+    ts: "typescript",
+    tsx: "typescript",
+    js: "javascript",
+    jsx: "javascript",
+    py: "python",
+    sh: "bash",
+    bash: "bash",
+    json: "json",
+    html: "html",
+    css: "css",
+    md: "markdown",
+    yaml: "yaml",
+    yml: "yaml",
+    sql: "sql",
+    rs: "rust",
+    go: "go",
+    cpp: "cpp",
+    cc: "cpp",
+    cxx: "cpp",
+    hpp: "cpp",
+    h: "cpp",
+    c: "c",
+    java: "java",
+    cs: "csharp",
+    php: "php",
+    rb: "ruby",
+    swift: "swift",
+    kt: "kotlin",
+  }
+  return ext ? langMap[ext] : undefined
+}
+
 export default function ToolCall(props: ToolCallProps) {
   const toolCallId = () => props.toolCallId || props.toolCall?.id || ""
   const expanded = () => isToolCallExpanded(toolCallId())
@@ -263,11 +300,8 @@ export default function ToolCall(props: ToolCallProps) {
     if (preview && input.filePath) {
       const lines = preview.split("\n")
       const truncated = lines.slice(0, 6).join("\n")
-      return (
-        <pre class="tool-call-content">
-          <code>{truncated}</code>
-        </pre>
-      )
+      const language = getLanguageFromPath(input.filePath)
+      return <CodeBlockInline code={truncated} language={language} />
     }
 
     return null
@@ -281,9 +315,7 @@ export default function ToolCall(props: ToolCallProps) {
     if (diff) {
       return (
         <div class="tool-call-diff">
-          <pre class="tool-call-content">
-            <code>{diff}</code>
-          </pre>
+          <CodeBlockInline code={diff} language="diff" />
         </div>
       )
     }
@@ -298,11 +330,8 @@ export default function ToolCall(props: ToolCallProps) {
     if (input.content && input.filePath) {
       const lines = input.content.split("\n")
       const truncated = lines.slice(0, 10).join("\n")
-      return (
-        <pre class="tool-call-content">
-          <code>{truncated}</code>
-        </pre>
-      )
+      const language = getLanguageFromPath(input.filePath)
+      return <CodeBlockInline code={truncated} language={language} />
     }
 
     return null
@@ -315,15 +344,10 @@ export default function ToolCall(props: ToolCallProps) {
     const output = metadata.output
 
     if (input.command) {
+      const fullOutput = `$ ${input.command}${output ? "\n" + output : ""}`
       return (
         <div class="tool-call-bash">
-          <pre class="tool-call-content">
-            <code>
-              $ {input.command}
-              {output && "\n"}
-              {output}
-            </code>
-          </pre>
+          <CodeBlockInline code={fullOutput} language="bash" />
         </div>
       )
     }
@@ -338,11 +362,7 @@ export default function ToolCall(props: ToolCallProps) {
     if (output) {
       const lines = output.split("\n")
       const truncated = lines.slice(0, 10).join("\n")
-      return (
-        <pre class="tool-call-content">
-          <code>{truncated}</code>
-        </pre>
-      )
+      return <CodeBlockInline code={truncated} language="markdown" />
     }
 
     return null
@@ -428,11 +448,7 @@ export default function ToolCall(props: ToolCallProps) {
     if (output) {
       const lines = output.split("\n")
       const truncated = lines.slice(0, 10).join("\n")
-      return (
-        <pre class="tool-call-content">
-          <code>{truncated}</code>
-        </pre>
-      )
+      return <CodeBlockInline code={truncated} />
     }
 
     return null
diff --git a/src/index.css b/src/index.css
index f9522b54..477bbdd4 100644
--- a/src/index.css
+++ b/src/index.css
@@ -195,10 +195,8 @@ body {
 .message-text {
   font-size: 14px;
   line-height: 1.5;
-  white-space: pre-wrap;
   word-wrap: break-word;
   overflow-wrap: break-word;
-  hyphens: auto;
 }
 
 .message-text pre {
@@ -753,3 +751,281 @@ body {
   font-style: italic;
   margin-top: 4px;
 }
+
+.prose {
+  color: #1a1a1a;
+}
+
+.prose code {
+  background-color: #f1f5f9;
+  color: #1e293b;
+  padding: 2px 6px;
+  border-radius: 4px;
+  font-size: 0.9em;
+  font-family: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, "Liberation Mono", monospace;
+}
+
+.prose pre {
+  background-color: transparent;
+  padding: 0;
+  margin: 0;
+  overflow: visible;
+}
+
+.prose pre code {
+  background: transparent;
+  padding: 0;
+  border-radius: 0;
+  font-size: 0.875em;
+}
+
+.prose a {
+  color: #0066ff;
+  text-decoration: none;
+}
+
+.prose a:hover {
+  text-decoration: underline;
+}
+
+.prose blockquote {
+  border-left: 4px solid #e0e0e0;
+  padding-left: 16px;
+  font-style: italic;
+  color: #666;
+  margin: 12px 0;
+}
+
+.prose ul,
+.prose ol {
+  margin: 8px 0;
+  padding-left: 24px;
+}
+
+.prose ul {
+  list-style-type: disc;
+}
+
+.prose ol {
+  list-style-type: decimal;
+}
+
+.prose li {
+  margin: 4px 0;
+}
+
+.prose h1 {
+  font-size: 1.5em;
+  font-weight: 700;
+  margin: 16px 0 12px 0;
+  line-height: 1.3;
+}
+
+.prose h2 {
+  font-size: 1.25em;
+  font-weight: 700;
+  margin: 14px 0 10px 0;
+  line-height: 1.3;
+}
+
+.prose h3 {
+  font-size: 1.1em;
+  font-weight: 600;
+  margin: 12px 0 8px 0;
+  line-height: 1.3;
+}
+
+.prose table {
+  border-collapse: collapse;
+  width: 100%;
+  margin: 12px 0;
+  font-size: 0.9em;
+}
+
+.prose th {
+  border: 1px solid #e0e0e0;
+  padding: 8px 12px;
+  background-color: #f5f5f5;
+  font-weight: 600;
+  text-align: left;
+}
+
+.prose td {
+  border: 1px solid #e0e0e0;
+  padding: 8px 12px;
+}
+
+.prose p {
+  margin: 8px 0;
+}
+
+.prose hr {
+  border: none;
+  border-top: 1px solid #e0e0e0;
+  margin: 16px 0;
+}
+
+[data-theme="dark"] .prose {
+  color: #e0e0e0;
+}
+
+[data-theme="dark"] .prose code {
+  background-color: #2a2a2a;
+  color: #e0e0e0;
+}
+
+[data-theme="dark"] .prose a {
+  color: #0080ff;
+}
+
+[data-theme="dark"] .prose blockquote {
+  border-left-color: #3a3a3a;
+  color: #999;
+}
+
+[data-theme="dark"] .prose th {
+  border-color: #3a3a3a;
+  background-color: #2a2a2a;
+}
+
+[data-theme="dark"] .prose td {
+  border-color: #3a3a3a;
+}
+
+[data-theme="dark"] .prose hr {
+  border-top-color: #3a3a3a;
+}
+
+.markdown-code-block {
+  position: relative;
+  margin: 12px 0;
+  border-radius: 6px;
+  overflow: hidden;
+  background-color: #f8f9fa;
+  border: 1px solid #e0e0e0;
+}
+
+[data-theme="dark"] .markdown-code-block {
+  background-color: #1a1a1a;
+  border-color: #3a3a3a;
+}
+
+.code-block-header {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  padding: 8px 12px;
+  background-color: #f1f5f9;
+  border-bottom: 1px solid #e0e0e0;
+}
+
+[data-theme="dark"] .code-block-header {
+  background-color: #2a2a2a;
+  border-bottom-color: #3a3a3a;
+}
+
+.code-block-language {
+  font-size: 12px;
+  font-family: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, "Liberation Mono", monospace;
+  color: #666;
+  font-weight: 500;
+  text-transform: uppercase;
+}
+
+[data-theme="dark"] .code-block-language {
+  color: #999;
+}
+
+.code-block-copy {
+  display: flex;
+  align-items: center;
+  gap: 4px;
+  padding: 4px 8px;
+  font-size: 12px;
+  background-color: transparent;
+  border: 1px solid #e0e0e0;
+  border-radius: 4px;
+  cursor: pointer;
+  color: #666;
+  transition: all 150ms ease;
+}
+
+[data-theme="dark"] .code-block-copy {
+  border-color: #3a3a3a;
+  color: #999;
+}
+
+.code-block-copy:hover {
+  background-color: #e0e0e0;
+  border-color: #ccc;
+}
+
+[data-theme="dark"] .code-block-copy:hover {
+  background-color: #3a3a3a;
+  border-color: #4a4a4a;
+}
+
+.code-block-copy .copy-icon {
+  width: 14px;
+  height: 14px;
+}
+
+.code-block-copy .copy-text {
+  font-family: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, "Liberation Mono", monospace;
+}
+
+.markdown-code-block pre {
+  margin: 0 !important;
+  padding: 12px !important;
+  overflow-x: auto;
+  background-color: transparent !important;
+}
+
+.markdown-code-block code {
+  background: transparent !important;
+  padding: 0 !important;
+  font-size: 13px !important;
+  line-height: 1.6;
+}
+
+.code-block-inline {
+  position: relative;
+  margin: 8px 0;
+  border-radius: 6px;
+  overflow: hidden;
+  background-color: #f8f9fa;
+  border: 1px solid #e0e0e0;
+}
+
+[data-theme="dark"] .code-block-inline {
+  background-color: #1a1a1a;
+  border-color: #3a3a3a;
+}
+
+.code-block-inline .code-block-header {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  padding: 6px 10px;
+  background-color: #f1f5f9;
+  border-bottom: 1px solid #e0e0e0;
+}
+
+[data-theme="dark"] .code-block-inline .code-block-header {
+  background-color: #2a2a2a;
+  border-bottom-color: #3a3a3a;
+}
+
+.code-block-inline pre {
+  margin: 0 !important;
+  padding: 10px !important;
+  overflow-x: auto;
+  background-color: transparent !important;
+}
+
+.code-block-inline code {
+  background: transparent !important;
+  padding: 0 !important;
+  font-size: 12px !important;
+  line-height: 1.5;
+}
diff --git a/src/lib/markdown.ts b/src/lib/markdown.ts
new file mode 100644
index 00000000..4d4df5d4
--- /dev/null
+++ b/src/lib/markdown.ts
@@ -0,0 +1,98 @@
+import { marked } from "marked"
+import { getHighlighter, type Highlighter } from "shiki"
+
+let highlighter: Highlighter | null = null
+let currentTheme: "light" | "dark" = "light"
+
+async function getOrCreateHighlighter() {
+  if (!highlighter) {
+    highlighter = await getHighlighter({
+      themes: ["github-light", "github-dark"],
+      langs: [
+        "typescript",
+        "javascript",
+        "python",
+        "bash",
+        "json",
+        "html",
+        "css",
+        "markdown",
+        "yaml",
+        "sql",
+        "rust",
+        "go",
+        "cpp",
+        "c",
+        "java",
+        "csharp",
+        "php",
+        "ruby",
+        "swift",
+        "kotlin",
+        "diff",
+        "shell",
+      ],
+    })
+  }
+  return highlighter
+}
+
+export async function initMarkdown(isDark: boolean) {
+  const hl = await getOrCreateHighlighter()
+  currentTheme = isDark ? "dark" : "light"
+
+  marked.setOptions({
+    breaks: true,
+    gfm: true,
+  })
+
+  const renderer = new marked.Renderer()
+
+  renderer.code = (code: string, lang: string | undefined) => {
+    const encodedCode = encodeURIComponent(code)
+    const escapedLang = lang ? escapeHtml(lang) : ""
+
+    if (!lang) {
+      return `<div class="markdown-code-block" data-language="" data-code="${encodedCode}"><pre><code>${escapeHtml(code)}</code></pre></div>`
+    }
+
+    try {
+      const html = hl.codeToHtml(code, {
+        lang,
+        theme: isDark ? "github-dark" : "github-light",
+      })
+      return `<div class="markdown-code-block" data-language="${escapedLang}" data-code="${encodedCode}">${html}</div>`
+    } catch {
+      return `<div class="markdown-code-block" data-language="${escapedLang}" data-code="${encodedCode}"><pre><code class="language-${escapedLang}">${escapeHtml(code)}</code></pre></div>`
+    }
+  }
+
+  renderer.link = (href: string, title: string | null | undefined, text: string) => {
+    const titleAttr = title ? ` title="${escapeHtml(title)}"` : ""
+    return `<a href="${escapeHtml(href)}" target="_blank" rel="noopener noreferrer"${titleAttr}>${text}</a>`
+  }
+
+  renderer.codespan = (code: string) => {
+    return `<code class="inline-code">${escapeHtml(code)}</code>`
+  }
+
+  marked.use({ renderer })
+}
+
+export async function renderMarkdown(content: string): Promise<string> {
+  if (!highlighter) {
+    await initMarkdown(currentTheme === "dark")
+  }
+  return marked.parse(content) as Promise<string>
+}
+
+function escapeHtml(text: string): string {
+  const map: Record<string, string> = {
+    "&": "&amp;",
+    "<": "&lt;",
+    ">": "&gt;",
+    '"': "&quot;",
+    "'": "&#039;",
+  }
+  return text.replace(/[&<>"']/g, (m) => map[m])
+}
diff --git a/src/lib/theme.tsx b/src/lib/theme.tsx
new file mode 100644
index 00000000..8b024721
--- /dev/null
+++ b/src/lib/theme.tsx
@@ -0,0 +1,49 @@
+import { createContext, createSignal, useContext, onMount, type JSX } from "solid-js"
+
+interface ThemeContextValue {
+  isDark: () => boolean
+  toggleTheme: () => void
+  setTheme: (dark: boolean) => void
+}
+
+const ThemeContext = createContext<ThemeContextValue>()
+
+export function ThemeProvider(props: { children: JSX.Element }) {
+  const prefersDark = window.matchMedia("(prefers-color-scheme: dark)").matches
+  const savedTheme = localStorage.getItem("theme")
+  const initialDark = savedTheme ? savedTheme === "dark" : prefersDark
+
+  const [isDark, setIsDarkSignal] = createSignal(initialDark)
+
+  onMount(() => {
+    if (isDark()) {
+      document.documentElement.setAttribute("data-theme", "dark")
+    } else {
+      document.documentElement.removeAttribute("data-theme")
+    }
+  })
+
+  const setTheme = (dark: boolean) => {
+    setIsDarkSignal(dark)
+    localStorage.setItem("theme", dark ? "dark" : "light")
+    if (dark) {
+      document.documentElement.setAttribute("data-theme", "dark")
+    } else {
+      document.documentElement.removeAttribute("data-theme")
+    }
+  }
+
+  const toggleTheme = () => {
+    setTheme(!isDark())
+  }
+
+  return <ThemeContext.Provider value={{ isDark, toggleTheme, setTheme }}>{props.children}</ThemeContext.Provider>
+}
+
+export function useTheme() {
+  const context = useContext(ThemeContext)
+  if (!context) {
+    throw new Error("useTheme must be used within ThemeProvider")
+  }
+  return context
+}
diff --git a/src/main.tsx b/src/main.tsx
index 470e224a..ff044f22 100644
--- a/src/main.tsx
+++ b/src/main.tsx
@@ -1,5 +1,6 @@
 import { render } from "solid-js/web"
 import App from "./App"
+import { ThemeProvider } from "./lib/theme"
 import "./index.css"
 
 const root = document.getElementById("root")
@@ -8,4 +9,11 @@ if (!root) {
   throw new Error("Root element not found")
 }
 
-render(() => <App />, root)
+render(
+  () => (
+    <ThemeProvider>
+      <App />
+    </ThemeProvider>
+  ),
+  root,
+)
diff --git a/tasks/done/012-markdown-rendering.md b/tasks/done/012-markdown-rendering.md
new file mode 100644
index 00000000..e3638c8c
--- /dev/null
+++ b/tasks/done/012-markdown-rendering.md
@@ -0,0 +1,417 @@
+# Task 012: Markdown Rendering
+
+**Status:** Todo  
+**Estimated Time:** 3-4 hours  
+**Phase:** 3 - Essential Features  
+**Dependencies:** 007 (Message Display)
+
+## Overview
+
+Implement proper markdown rendering for assistant messages with syntax-highlighted code blocks. Replace basic text display with rich markdown formatting using Marked and Shiki.
+
+## Context
+
+Currently messages display as plain text. We need to parse and render markdown content from assistant messages, including:
+
+- Headings, bold, italic, links
+- Code blocks with syntax highlighting
+- Inline code
+- Lists (ordered and unordered)
+- Blockquotes
+- Tables (if needed)
+
+## Requirements
+
+### Functional Requirements
+
+1. **Markdown Parser Integration**
+   - Use `marked` library for markdown parsing
+   - Configure for safe HTML rendering
+   - Support GitHub-flavored markdown
+
+2. **Syntax Highlighting**
+   - Use `shiki` for code block highlighting
+   - Support light and dark themes
+   - Support common languages: TypeScript, JavaScript, Python, Bash, JSON, HTML, CSS, etc.
+
+3. **Code Block Features**
+   - Language label displayed
+   - Copy button on hover
+   - Line numbers (optional for MVP)
+
+4. **Inline Code**
+   - Distinct background color
+   - Monospace font
+   - Subtle padding
+
+5. **Links**
+   - Open in external browser
+   - Show external link icon
+   - Prevent opening in same window
+
+### Technical Requirements
+
+1. **Dependencies**
+   - Install `marked` and `@types/marked`
+   - Install `shiki`
+   - Install `marked-highlight` for integration
+
+2. **Theme Support**
+   - Light mode: `github-light` theme
+   - Dark mode: `github-dark` theme
+   - Respect system theme preference
+
+3. **Security**
+   - Sanitize HTML output
+   - No script execution
+   - Safe link handling
+
+4. **Performance**
+   - Lazy load Shiki highlighter
+   - Cache highlighter instance
+   - Don't re-parse unchanged messages
+
+## Implementation Steps
+
+### Step 1: Install Dependencies
+
+```bash
+cd packages/opencode-client
+npm install marked shiki
+npm install -D @types/marked
+```
+
+### Step 2: Create Markdown Utility
+
+Create `src/lib/markdown.ts`:
+
+```typescript
+import { marked } from "marked"
+import { getHighlighter, type Highlighter } from "shiki"
+
+let highlighter: Highlighter | null = null
+
+async function getOrCreateHighlighter() {
+  if (!highlighter) {
+    highlighter = await getHighlighter({
+      themes: ["github-light", "github-dark"],
+      langs: ["typescript", "javascript", "python", "bash", "json", "html", "css", "markdown", "yaml", "sql"],
+    })
+  }
+  return highlighter
+}
+
+export async function initMarkdown(isDark: boolean) {
+  const hl = await getOrCreateHighlighter()
+
+  marked.use({
+    async: false,
+    breaks: true,
+    gfm: true,
+  })
+
+  const renderer = new marked.Renderer()
+
+  renderer.code = (code: string, language: string | undefined) => {
+    if (!language) {
+      return `<pre><code>${escapeHtml(code)}</code></pre>`
+    }
+
+    try {
+      const html = hl.codeToHtml(code, {
+        lang: language,
+        theme: isDark ? "github-dark" : "github-light",
+      })
+      return html
+    } catch (e) {
+      return `<pre><code class="language-${language}">${escapeHtml(code)}</code></pre>`
+    }
+  }
+
+  renderer.link = (href: string, title: string | null, text: string) => {
+    const titleAttr = title ? ` title="${escapeHtml(title)}"` : ""
+    return `<a href="${escapeHtml(href)}" target="_blank" rel="noopener noreferrer"${titleAttr}>${text}</a>`
+  }
+
+  marked.use({ renderer })
+}
+
+export function renderMarkdown(content: string): string {
+  return marked.parse(content) as string
+}
+
+function escapeHtml(text: string): string {
+  const map: Record<string, string> = {
+    "&": "&amp;",
+    "<": "&lt;",
+    ">": "&gt;",
+    '"': "&quot;",
+    "'": "&#039;",
+  }
+  return text.replace(/[&<>"']/g, (m) => map[m])
+}
+```
+
+### Step 3: Create Markdown Component
+
+Create `src/components/markdown.tsx`:
+
+```typescript
+import { createEffect, createSignal, onMount } from 'solid-js'
+import { initMarkdown, renderMarkdown } from '../lib/markdown'
+
+interface MarkdownProps {
+  content: string
+  isDark?: boolean
+}
+
+export function Markdown(props: MarkdownProps) {
+  const [html, setHtml] = createSignal('')
+  const [ready, setReady] = createSignal(false)
+
+  onMount(async () => {
+    await initMarkdown(props.isDark ?? false)
+    setReady(true)
+  })
+
+  createEffect(() => {
+    if (ready()) {
+      const rendered = renderMarkdown(props.content)
+      setHtml(rendered)
+    }
+  })
+
+  createEffect(async () => {
+    if (props.isDark !== undefined) {
+      await initMarkdown(props.isDark)
+      const rendered = renderMarkdown(props.content)
+      setHtml(rendered)
+    }
+  })
+
+  return (
+    <div
+      class="prose prose-sm dark:prose-invert max-w-none"
+      innerHTML={html()}
+    />
+  )
+}
+```
+
+### Step 4: Add Copy Button to Code Blocks
+
+Create `src/components/code-block.tsx`:
+
+```typescript
+import { createSignal, Show } from 'solid-js'
+
+interface CodeBlockProps {
+  code: string
+  language?: string
+}
+
+export function CodeBlockWrapper(props: CodeBlockProps) {
+  const [copied, setCopied] = createSignal(false)
+
+  const copyCode = async () => {
+    await navigator.clipboard.writeText(props.code)
+    setCopied(true)
+    setTimeout(() => setCopied(false), 2000)
+  }
+
+  return (
+    <div class="relative group">
+      <div class="absolute top-2 right-2 opacity-0 group-hover:opacity-100 transition-opacity">
+        <button
+          onClick={copyCode}
+          class="px-2 py-1 text-xs bg-gray-700 text-white rounded hover:bg-gray-600"
+        >
+          <Show when={copied()} fallback="Copy">
+            Copied!
+          </Show>
+        </button>
+      </div>
+      <Show when={props.language}>
+        <div class="text-xs text-gray-500 dark:text-gray-400 px-4 pt-2">
+          {props.language}
+        </div>
+      </Show>
+      <div innerHTML={props.code} />
+    </div>
+  )
+}
+```
+
+### Step 5: Update Message Component
+
+Update `src/components/message-item.tsx` to use Markdown component:
+
+```typescript
+import { Markdown } from './markdown'
+
+// In the assistant message rendering:
+<For each={textParts()}>
+  {(part) => (
+    <Markdown
+      content={part.content}
+      isDark={/* get from theme context */}
+    />
+  )}
+</For>
+```
+
+### Step 6: Add Markdown Styles
+
+Add to `src/index.css`:
+
+```css
+/* Markdown prose styles */
+.prose {
+  @apply text-gray-900 dark:text-gray-100;
+}
+
+.prose code {
+  @apply bg-gray-100 dark:bg-gray-800 px-1.5 py-0.5 rounded text-sm;
+}
+
+.prose pre {
+  @apply bg-gray-50 dark:bg-gray-900 rounded-lg p-4 overflow-x-auto;
+}
+
+.prose pre code {
+  @apply bg-transparent p-0;
+}
+
+.prose a {
+  @apply text-blue-600 dark:text-blue-400 hover:underline;
+}
+
+.prose blockquote {
+  @apply border-l-4 border-gray-300 dark:border-gray-700 pl-4 italic;
+}
+
+.prose ul {
+  @apply list-disc list-inside;
+}
+
+.prose ol {
+  @apply list-decimal list-inside;
+}
+
+.prose h1 {
+  @apply text-2xl font-bold mb-4;
+}
+
+.prose h2 {
+  @apply text-xl font-bold mb-3;
+}
+
+.prose h3 {
+  @apply text-lg font-bold mb-2;
+}
+
+.prose table {
+  @apply border-collapse w-full;
+}
+
+.prose th {
+  @apply border border-gray-300 dark:border-gray-700 px-4 py-2 bg-gray-100 dark:bg-gray-800;
+}
+
+.prose td {
+  @apply border border-gray-300 dark:border-gray-700 px-4 py-2;
+}
+```
+
+### Step 7: Handle Theme Changes
+
+Create or update theme context to track light/dark mode:
+
+```typescript
+import { createContext, createSignal, useContext } from 'solid-js'
+
+const ThemeContext = createContext<{
+  isDark: () => boolean
+  toggleTheme: () => void
+}>()
+
+export function ThemeProvider(props: { children: any }) {
+  const prefersDark = window.matchMedia('(prefers-color-scheme: dark)').matches
+  const [isDark, setIsDark] = createSignal(prefersDark)
+
+  const toggleTheme = () => {
+    setIsDark(!isDark())
+    document.documentElement.classList.toggle('dark')
+  }
+
+  return (
+    <ThemeContext.Provider value={{ isDark, toggleTheme }}>
+      {props.children}
+    </ThemeContext.Provider>
+  )
+}
+
+export function useTheme() {
+  const context = useContext(ThemeContext)
+  if (!context) {
+    throw new Error('useTheme must be used within ThemeProvider')
+  }
+  return context
+}
+```
+
+### Step 8: Test Markdown Rendering
+
+Test with various markdown inputs:
+
+1. **Headings**: `# Heading 1\n## Heading 2`
+2. **Code blocks**: ` ```typescript\nconst x = 1\n``` `
+3. **Inline code**: `` `npm install` ``
+4. **Lists**: `- Item 1\n- Item 2`
+5. **Links**: `[OpenCode](https://opencode.ai)`
+6. **Bold/Italic**: `**bold** and *italic*`
+7. **Blockquotes**: `> Quote`
+
+## Acceptance Criteria
+
+- [ ] Markdown content renders with proper formatting
+- [ ] Code blocks have syntax highlighting
+- [ ] Light and dark themes work correctly
+- [ ] Copy button appears on code block hover
+- [ ] Copy button successfully copies code to clipboard
+- [ ] Language label shows for code blocks
+- [ ] Inline code has distinct styling
+- [ ] Links open in external browser
+- [ ] No XSS vulnerabilities (sanitized output)
+- [ ] Theme changes update code highlighting
+- [ ] Headings, lists, blockquotes render correctly
+- [ ] Performance is acceptable (no lag when rendering)
+
+## Testing Checklist
+
+- [ ] Test all markdown syntax types
+- [ ] Test code blocks with various languages
+- [ ] Test switching between light and dark mode
+- [ ] Test copy functionality
+- [ ] Test external link opening
+- [ ] Test very long code blocks (scrolling)
+- [ ] Test malformed markdown
+- [ ] Test HTML in markdown (should be escaped)
+
+## Notes
+
+- Shiki loads language grammars asynchronously, so first render may be slower
+- Consider caching rendered markdown if re-rendering same content
+- For MVP, don't implement line numbers or advanced code block features
+- Keep the language list limited to common ones to reduce bundle size
+
+## Future Enhancements (Post-MVP)
+
+- Line numbers in code blocks
+- Code block diff highlighting
+- Collapsible long code blocks
+- Search within code blocks
+- More language support
+- Custom syntax themes
+- LaTeX/Math rendering
+- Mermaid diagram support