diff --git a/bump_pydantic/main.py b/bump_pydantic/main.py
index d387f02..3bdfe30 100644
--- a/bump_pydantic/main.py
+++ b/bump_pydantic/main.py
@@ -1,17 +1,17 @@
+import difflib
 import functools
-import logging
 import multiprocessing
 import os
 import time
 import traceback
 from pathlib import Path
-from typing import Any, Dict, List, Type, TypeVar, Union
+from typing import Any, Dict, Iterable, List, Tuple, Type, TypeVar, Union
 
 import libcst as cst
 from libcst.codemod import CodemodContext, ContextAwareTransformer
 from libcst.helpers import calculate_module_and_package
 from libcst.metadata import FullRepoManager, FullyQualifiedNameProvider, ScopeProvider
-from rich.logging import RichHandler
+from rich.console import Console
 from rich.progress import Progress
 from typer import Argument, Exit, Option, Typer, echo
 from typing_extensions import ParamSpec
@@ -30,10 +30,6 @@
 T = TypeVar("T")
 
 
-logging.basicConfig(level="INFO", format="%(message)s", datefmt="[%X]", handlers=[RichHandler()])
-logger = logging.getLogger("bump_pydantic")
-
-
 def version_callback(value: bool):
     if value:
         echo(f"bump-pydantic version: {__version__}")
@@ -44,6 +40,7 @@ def version_callback(value: bool):
 def main(
     path: Path = Argument(..., exists=True, dir_okay=True, allow_dash=False),
     disable: List[Rule] = Option(default=[], help="Disable a rule."),
+    diff: bool = Option(False, help="Show diff instead of applying changes."),
     log_file: Path = Option("log.txt", help="Log errors to this file."),
     version: bool = Option(
         None,
@@ -53,7 +50,8 @@ def main(
         help="Show the version and exit.",
     ),
 ):
-    logger.info("Start bump-pydantic.")
+    console = Console(log_time=True)
+    console.log("Start bump-pydantic.")
     # NOTE: LIBCST_PARSER_TYPE=native is required according to https://github.com/Instagram/LibCST/issues/487.
     os.environ["LIBCST_PARSER_TYPE"] = "native"
 
@@ -65,42 +63,53 @@ def main(
         files_str = list(package.glob("**/*.py"))
         files = [str(file.relative_to(".")) for file in files_str]
 
-    logger.info(f"Found {len(files)} files to process.")
+    console.log(f"Found {len(files)} files to process")
 
     providers = {FullyQualifiedNameProvider, ScopeProvider}
     metadata_manager = FullRepoManager(".", files, providers=providers)  # type: ignore[arg-type]
     metadata_manager.resolve_cache()
 
-    logger.info("Running mypy to get type information. This may take a while...")
+    console.log("Running mypy to get type information. This may take a while...")
     classes = run_mypy_visitor(files)
     scratch: dict[str, Any] = {CONTEXT_KEY: classes}
-    logger.info("Finished mypy.")
+    console.log("Finished mypy.")
 
     start_time = time.time()
 
     codemods = gather_codemods(disabled=disable)
 
     log_fp = log_file.open("a+")
-    partial_run_codemods = functools.partial(run_codemods, codemods, metadata_manager, scratch, package)
+    partial_run_codemods = functools.partial(run_codemods, codemods, metadata_manager, scratch, package, diff)
     with Progress(*Progress.get_default_columns(), transient=True) as progress:
         task = progress.add_task(description="Executing codemods...", total=len(files))
         count_errors = 0
+        difflines: List[List[str]] = []
         with multiprocessing.Pool() as pool:
-            for error in pool.imap_unordered(partial_run_codemods, files):
+            for error, _difflines in pool.imap_unordered(partial_run_codemods, files):
                 progress.advance(task)
+
+                if _difflines is not None:
+                    difflines.append(_difflines)
+
                 if error is not None:
                     count_errors += 1
                     log_fp.writelines(error)
 
     modified = [Path(f) for f in files if os.stat(f).st_mtime > start_time]
 
-    if modified:
-        logger.info(f"Refactored {len(modified)} files.")
+    if modified and not diff:
+        console.log(f"Refactored {len(modified)} files.")
+
+    for _difflines in difflines:
+        color_diff(console, _difflines)
 
     if count_errors > 0:
-        logger.info(f"Found {count_errors} errors. Please check the {log_file} file.")
+        console.log(f"Found {count_errors} errors. Please check the {log_file} file.")
     else:
-        logger.info("Run successfully!")
+        console.log("Run successfully!")
+
+    if difflines:
+        raise Exit(1)
 
 
 def run_codemods(
@@ -108,8 +117,9 @@ def run_codemods(
     metadata_manager: FullRepoManager,
     scratch: Dict[str, Any],
     package: Path,
+    diff: bool,
     filename: str,
-) -> Union[str, None]:
+) -> Tuple[Union[str, None], Union[List[str], None]]:
     try:
         module_and_package = calculate_module_and_package(str(package), filename)
         context = CodemodContext(
@@ -134,8 +144,30 @@ def run_codemods(
 
             output_code = input_tree.code
             if code != output_code:
-                fp.write(output_code)
-                fp.truncate()
-        return None
+                if diff:
+                    lines = difflib.unified_diff(
+                        code.splitlines(keepends=True),
+                        output_code.splitlines(keepends=True),
+                        fromfile=filename,
+                        tofile=filename,
+                    )
+                    return None, list(lines)
+                else:
+                    fp.write(output_code)
+                    fp.truncate()
+        return None, None
     except Exception:
-        return f"An error happened on {filename}.\n{traceback.format_exc()}"
+        return f"An error happened on {filename}.\n{traceback.format_exc()}", None
+
+
+def color_diff(console: Console, lines: Iterable[str]) -> None:
+    for line in lines:
+        line = line.rstrip("\n")
+        if line.startswith("+"):
+            console.print(line, style="green")
+        elif line.startswith("-"):
+            console.print(line, style="red")
+        elif line.startswith("^"):
+            console.print(line, style="blue")
+        else:
+            console.print(line, style="white")