diff --git a/cli/src/commands/debug/copy_detection.rs b/cli/src/commands/debug/copy_detection.rs
new file mode 100644
index 000000000..613baf8e7
--- /dev/null
+++ b/cli/src/commands/debug/copy_detection.rs
@@ -0,0 +1,79 @@
+// Copyright 2024 The Jujutsu Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#![allow(unused, dead_code)]
+
+use std::fmt::Debug;
+use std::io::Write as _;
+use std::path::{Path, PathBuf};
+
+use futures::executor::block_on_stream;
+use futures::StreamExt;
+use jj_lib::backend::{Backend, CopyRecord, CopySource, CopySources};
+use jj_lib::default_index::{AsCompositeIndex as _, DefaultIndexStore};
+use jj_lib::op_walk;
+use jj_lib::repo_path::{RepoPath, RepoPathBuf};
+
+use crate::cli_util::{CommandHelper, RevisionArg};
+use crate::command_error::{internal_error, user_error, CommandError};
+use crate::ui::Ui;
+
+/// Rebuild commit index
+#[derive(clap::Args, Clone, Debug)]
+pub struct CopyDetectionArgs {
+    /// Show changes in this revision, compared to its parent(s)
+    #[arg(default_value = "@")]
+    revision: RevisionArg,
+}
+
+pub fn cmd_debug_copy_detection(
+    ui: &mut Ui,
+    command: &CommandHelper,
+    args: &CopyDetectionArgs,
+) -> Result<(), CommandError> {
+    let ws = command.workspace_helper(ui)?;
+    let Some(git) = ws.git_backend() else {
+        writeln!(ui.stderr(), "Not a git backend.")?;
+        return Ok(());
+    };
+    let commit = ws.resolve_single_rev(&args.revision)?;
+    let tree = commit.tree()?;
+
+    let paths: Vec<RepoPathBuf> = tree.entries().map(|(path, _)| path).collect();
+    let commits = [commit.id().clone()];
+    let parents = commit.parent_ids();
+    for copy_record in
+        block_on_stream(git.get_copy_records(&paths, parents, &commits)?).filter_map(|r| r.ok())
+    {
+        match copy_record.sources {
+            CopySources::Resolved(CopySource { path, .. }) => {
+                write!(ui.stdout(), "{}", path.as_internal_file_string());
+            }
+            CopySources::Conflict(conflicting) => {
+                let mut sorted: Vec<_> = conflicting
+                    .iter()
+                    .map(|s| s.path.as_internal_file_string())
+                    .collect();
+                sorted.sort();
+                write!(ui.stdout(), "{{ {} }}", sorted.join(", "));
+            }
+        }
+        writeln!(
+            ui.stdout(),
+            " -> {}",
+            copy_record.target.as_internal_file_string()
+        );
+    }
+    Ok(())
+}
diff --git a/cli/src/commands/debug/mod.rs b/cli/src/commands/debug/mod.rs
index 97138e2fa..3f09819d3 100644
--- a/cli/src/commands/debug/mod.rs
+++ b/cli/src/commands/debug/mod.rs
@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+pub mod copy_detection;
 pub mod fileset;
 pub mod index;
 pub mod local_working_copy;
@@ -30,6 +31,7 @@ use std::fmt::Debug;
 use clap::Subcommand;
 use jj_lib::local_working_copy::LocalWorkingCopy;
 
+use self::copy_detection::{cmd_debug_copy_detection, CopyDetectionArgs};
 use self::fileset::{cmd_debug_fileset, DebugFilesetArgs};
 use self::index::{cmd_debug_index, DebugIndexArgs};
 use self::local_working_copy::{cmd_debug_local_working_copy, DebugLocalWorkingCopyArgs};
@@ -49,6 +51,7 @@ use crate::ui::Ui;
 #[derive(Subcommand, Clone, Debug)]
 #[command(hide = true)]
 pub enum DebugCommand {
+    CopyDetection(CopyDetectionArgs),
     Fileset(DebugFilesetArgs),
     Index(DebugIndexArgs),
     LocalWorkingCopy(DebugLocalWorkingCopyArgs),
@@ -75,6 +78,7 @@ pub fn cmd_debug(
         DebugCommand::LocalWorkingCopy(args) => cmd_debug_local_working_copy(ui, command, args),
         DebugCommand::Operation(args) => cmd_debug_operation(ui, command, args),
         DebugCommand::Reindex(args) => cmd_debug_reindex(ui, command, args),
+        DebugCommand::CopyDetection(args) => cmd_debug_copy_detection(ui, command, args),
         DebugCommand::Revset(args) => cmd_debug_revset(ui, command, args),
         DebugCommand::Snapshot(args) => cmd_debug_snapshot(ui, command, args),
         DebugCommand::Template(args) => cmd_debug_template(ui, command, args),
diff --git a/cli/tests/runner.rs b/cli/tests/runner.rs
index c143db097..1f6b87bd1 100644
--- a/cli/tests/runner.rs
+++ b/cli/tests/runner.rs
@@ -19,6 +19,7 @@ mod test_commit_command;
 mod test_commit_template;
 mod test_concurrent_operations;
 mod test_config_command;
+mod test_copy_detection;
 mod test_debug_command;
 mod test_describe_command;
 mod test_diff_command;
diff --git a/cli/tests/test_copy_detection.rs b/cli/tests/test_copy_detection.rs
new file mode 100644
index 000000000..f72849306
--- /dev/null
+++ b/cli/tests/test_copy_detection.rs
@@ -0,0 +1,34 @@
+// Copyright 2022 The Jujutsu Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use crate::common::TestEnvironment;
+
+#[test]
+fn test_simple_rename() {
+    let test_env = TestEnvironment::default();
+    test_env.jj_cmd_ok(test_env.env_root(), &["git", "init", "repo"]);
+    let repo_path = test_env.env_root().join("repo");
+
+    test_env.jj_cmd_ok(&repo_path, &["new"]);
+    std::fs::write(repo_path.join("original"), "original").unwrap();
+    std::fs::write(repo_path.join("something"), "something").unwrap();
+    test_env.jj_cmd_ok(&repo_path, &["commit", "-mfirst"]);
+    std::fs::remove_file(repo_path.join("original")).unwrap();
+    std::fs::write(repo_path.join("modified"), "original").unwrap();
+    std::fs::write(repo_path.join("something"), "changed").unwrap();
+    insta::assert_snapshot!(test_env.jj_cmd_success(&repo_path, &["debug", "copy-detection"]).replace('\\', "/"),
+    @r###"
+    original -> modified
+    "###);
+}