diff --git a/backend/src/app_mixins/chat.py b/backend/src/app_mixins/chat.py
index def0d48..c9f7fbe 100644
--- a/backend/src/app_mixins/chat.py
+++ b/backend/src/app_mixins/chat.py
@@ -13,6 +13,7 @@ def message_json(msg):
         "sender": msg.sender,
         "kind": msg.kind,
         "subkind": msg.subkind,
+        "format": msg.format,
         "content": msg.content,
         "threadId": msg.thread_id,
     }
diff --git a/backend/src/server/websocket.py b/backend/src/server/websocket.py
index d3e1d3f..0887453 100644
--- a/backend/src/server/websocket.py
+++ b/backend/src/server/websocket.py
@@ -276,7 +276,7 @@ def register(server, app, auth_manager):
                 elif action == "update-chat-message":
                     message = await app.update_chat_message(
                         message_id=body['messageId'],
-                        content=body['content'],
+                        content=body.get('content'),
                         kind=body.get('kind'),
                         subkind=body.get('subkind'),
                         format=body.get('format'),
diff --git a/frontend/src/assets/main.css b/frontend/src/assets/main.css
index 248bfba..af0c2dc 100644
--- a/frontend/src/assets/main.css
+++ b/frontend/src/assets/main.css
@@ -94,4 +94,14 @@ input:disabled, textarea:disabled, select:disabled {
 
 .with-sidebar-expanded .when-sidebar-collapsed {
   display: none;
+}
+
+/* Content */
+h1, h2, h3, h4, h5, h6 {
+  margin: 1em 0 0.5em;
+  font-weight: bold;
+}
+
+p, ul, il {
+  margin: 0.5em 0;
 }
\ No newline at end of file
diff --git a/frontend/src/chat.js b/frontend/src/chat.js
index a696d07..f3665e5 100644
--- a/frontend/src/chat.js
+++ b/frontend/src/chat.js
@@ -545,6 +545,33 @@ export class ChatSession {
     this.creatingThread.value = Boolean(fork);
   }
 
+  // Sets the render format of a message ("markdown", or "" for plain text).
+  // Omit `content` so the backend leaves the existing content untouched.
+  setMessageFormat (message, format) {
+    backend.sendAction("update-chat-message", {
+      messageId: message.id, format,
+    }).then(response => {
+      if (response && response.error) {
+        ui.alert("Error updating message format: " + response.error);
+      }
+    });
+
+    // No update event is broadcast (matching the content-edit path above), so
+    // patch the source message and rebuild the entries locally. Other sessions
+    // and stale views won't reflect this until reload — which is correct, since
+    // the format is persisted. If we ever broadcast edits, flip this to rely on
+    // the incoming update instead.
+    let thread = this.getThread(message.threadId);
+    let existing = thread.messages.find(msg => msg.id == message.id);
+    if (existing) {
+      existing.format = format;
+    } else {
+      console.error("Can't set format locally?", {messageId: message.id, thread});
+    }
+
+    this.computeChatEntries();
+  }
+
   // Adds a bulk of messages to the message list, in their correct
   // chronological position and replacing duplicates
   addMessageBulk (messages) {
diff --git a/frontend/src/components/Message.vue b/frontend/src/components/Message.vue
index 9511de7..683ce3f 100644
--- a/frontend/src/components/Message.vue
+++ b/frontend/src/components/Message.vue
@@ -4,13 +4,17 @@ import { marked } from "marked";
 import * as backend from '../backend';
 marked.use({
   renderer: {
-    code (code, infostring, escaped) {
-      let langElem = infostring ? 
-        `<div class="language">${infostring}</div>` : "";
+    code ({lang, text}) {
+      let langElem = lang ? 
+        `<div class="code-lang">${lang}</div>` : "";
+
+      const div = document.createElement('div');
+      div.textContent = text;
+      const escaped = div.innerHTML;
 
       return `<div class="code">
         ${langElem}
-        <div class="content">${code}</div>
+        <div class="code-content">${escaped}</div>
       </div>`;
     }
   }
@@ -111,7 +115,7 @@ watch(() => [props.message.format, props.message.content], ([newFormat, newConte
     <template v-if="message.type == 'message' || message.type == null">
       <div v-if="message.sender != 'user'" class="sender">{{message.sender}}</div>
 
-      <div v-if="format == 'markdown'" v-html="marked.parse(message.content)" class="content"></div>
+      <div v-if="format == 'markdown'" v-html="marked.parse(message.content)" class="md-content" style="white-space: collapse;"></div>
       <div v-else class="content">{{content}}</div>
     </template>
 
@@ -189,14 +193,6 @@ watch(() => [props.message.format, props.message.content], ([newFormat, newConte
   margin-right: 2em;
 }
 
-.message .content {
-  white-space: preserve;
-}
-
-.message ul, .message ol {
-  white-space: normal;
-}
-
 .message .sender,
 .note .sender {
   font-weight: bold;
@@ -288,4 +284,38 @@ watch(() => [props.message.format, props.message.content], ([newFormat, newConte
   font-style: normal;
   font-weight: bold;
 }
+
+.md-content {
+  white-space: collapse;
+  width: fit-content;
+  max-width: 50em;
+  line-height: normal;
+  word-wrap: anywhere;
+}
+
+</style>
+
+<style>
+/* Code blocks are generated at runtime, these styles cannot be scoped */
+
+.code {
+  background-color: var(--color-surface-input);
+  border-radius: var(--border-radius);
+  margin: .5em 0;
+  padding: .5em;
+}
+
+.code-lang {
+  padding-bottom: .5em;
+  margin-top: -.5em;
+  font-weight: bold;
+  user-select: none;
+}
+
+.code-content {
+  white-space: pre;
+  font-family: monospace;
+  overflow-x: auto;
+  line-height: 1.6rem;
+}
 </style>
diff --git a/frontend/src/components/TitleBar.vue b/frontend/src/components/TitleBar.vue
index d228da8..b6c56f6 100644
--- a/frontend/src/components/TitleBar.vue
+++ b/frontend/src/components/TitleBar.vue
@@ -23,8 +23,8 @@
 <style scoped>
   :slotted(h1) {
     font-size: 160%;
-    font-weight: bold;
     padding: 0 0.4em;
+    margin: 0;
   }
 
   .main-header {
diff --git a/frontend/src/views/Chat.vue b/frontend/src/views/Chat.vue
index fe5f2e7..a44cea5 100644
--- a/frontend/src/views/Chat.vue
+++ b/frontend/src/views/Chat.vue
@@ -130,6 +130,12 @@
       {value: 'pin', title: "Pin message"},
       {value: 'edit', title: "Edit in-place"},
       {value: 'edit-fork', title: "Edit in new thread"},
+      // ContextMenu.vue uses null for "dismissed", so the "None" entry can't
+      // carry a null value; "format:" (empty suffix) is the sentinel for "".
+      {title: "Set format", entries: [
+        {value: 'format:markdown', title: "Markdown"},
+        {value: 'format:', title: "None"},
+      ]},
     ];
 
     // Long logs can be expanded/collapsed
@@ -164,6 +170,12 @@
         }
         break;
       }
+      default: {
+        if (selected?.startsWith('format:')) {
+          session.setMessageFormat(message, selected.slice('format:'.length));
+        }
+        break;
+      }
 
     }
   }