diff --git a/chatbot.py b/chatbot.py
index d6a8df1..6610687 100644
--- a/chatbot.py
+++ b/chatbot.py
@@ -22,10 +22,15 @@ SYSTEM_PROMPT = (
     "You are a knowledgeable developer assistant. Answer questions about "
     "programming languages, libraries, frameworks, tools, debugging, and "
     "software design with clear, accurate, and concise explanations. Use "
-    "code snippets when they help illustrate an answer. Use the web_search "
-    "tool when a question depends on current information you may not know "
-    "(recent releases, changelogs, current best practices, error messages "
-    "you don't recognize)."
+    "code snippets when they help illustrate an answer, and always place "
+    "them in fenced Markdown code blocks with a language tag right after "
+    "the opening backticks (e.g. ```python), never inline in a paragraph "
+    "or left unfenced. Use Markdown throughout: numbered or bulleted "
+    "lists for steps, **bold** for emphasis, and inline `code` spans for "
+    "identifiers, filenames, and commands mentioned in prose. Use the "
+    "web_search tool when a question depends on current information you "
+    "may not know (recent releases, changelogs, current best practices, "
+    "error messages you don't recognize)."
 )
 
 # Number of prior user/assistant exchanges to keep in the prompt. Bounds the
diff --git a/gui.py b/gui.py
index bc5bb66..6516256 100644
--- a/gui.py
+++ b/gui.py
@@ -93,7 +93,7 @@ def _highlight_code_lines(code: str, lang: str) -> list[str]:
             lexer = TextLexer()
     highlighted = highlight(code, lexer, _CODE_FORMATTER)
     lines = highlighted.rstrip("\n").split("\n")
-    return [f'<span style="color:{_CODE_FG};">{line}</span>' for line in lines]
+    return [f'<span style="color:{_CODE_FG}; white-space:pre;">{line}</span>' for line in lines]
 
 
 def _reset_cursor_format(cursor: QTextCursor) -> None: