diff --git a/Cargo.lock b/Cargo.lock
index e3c9836..d4d7ed7 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -616,6 +616,12 @@ dependencies = [
  "either",
 ]
 
+[[package]]
+name = "itoa"
+version = "1.0.15"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4a5f13b858c8d314ee3e8f639011f7ccefe71f97f96e50151fb991f267928e2c"
+
 [[package]]
 name = "jobserver"
 version = "0.1.33"
@@ -718,6 +724,8 @@ dependencies = [
  "rayon",
  "re-tex",
  "ree-pak-core",
+ "serde",
+ "serde_json",
 ]
 
 [[package]]
@@ -1183,6 +1191,12 @@ version = "1.0.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8a0d197bd2c9dc6e53b84da9556a69ba4cdfab8619eb41a8bd1cc2027a0f6b1d"
 
+[[package]]
+name = "ryu"
+version = "1.0.20"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "28d3b2b1366ec20994f1fd18c3c594f05c5dd4bc44d8bb0c1c632c8d6829481f"
+
 [[package]]
 name = "scopeguard"
 version = "1.2.0"
@@ -1209,6 +1223,18 @@ dependencies = [
  "syn 2.0.104",
 ]
 
+[[package]]
+name = "serde_json"
+version = "1.0.141"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "30b9eff21ebe718216c6ec64e1d9ac57087aad11efc64e32002bce4a0d4c03d3"
+dependencies = [
+ "itoa",
+ "memchr",
+ "ryu",
+ "serde",
+]
+
 [[package]]
 name = "serde_spanned"
 version = "0.6.9"
diff --git a/Cargo.toml b/Cargo.toml
index e501faa..1fc9173 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -18,3 +18,5 @@ rayon = "1.10"
 parking_lot = "0.12"
 colored = "3.0"
 fs-err = "3.1.1"
+serde = { version = "1.0.219", features = ["derive"] }
+serde_json = "1.0.141"
diff --git a/src/app.rs b/src/app.rs
index a82dd93..c26badd 100644
--- a/src/app.rs
+++ b/src/app.rs
@@ -24,7 +24,7 @@ use ree_pak_core::{
     write::FileOptions,
 };
 
-use crate::{chunk::ChunkName, util::human_bytes};
+use crate::{chunk::ChunkName, metadata::PakMetadata, util::human_bytes};
 
 const FILE_NAME_LIST: &[u8] = include_bytes!("../assets/MHWs_STM_Release.list.zst");
 const AUTO_CHUNK_SELECTION_SIZE_THRESHOLD: usize = 50 * 1024 * 1024; // 50MB
@@ -111,7 +111,15 @@ impl App {
             .truncate(true)
             .write(true)
             .open(output_path)?;
-        let pak_writer = ree_pak_core::write::PakWriter::new(out_file, entries.len() as u64);
+        let mut pak_writer = ree_pak_core::write::PakWriter::new(out_file, entries.len() as u64);
+
+        // write metadata
+        let metadata = PakMetadata {
+            version: 1,
+            is_uncompressed_patch: true,
+        };
+        metadata.write_to_pak(&mut pak_writer)?;
+
         let pak_writer_mtx = Arc::new(Mutex::new(pak_writer));
 
         let bar = ProgressBar::new(entries.len() as u64);
diff --git a/src/main.rs b/src/main.rs
index 66622a2..ba24cff 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,5 +1,6 @@
 mod app;
 mod chunk;
+mod metadata;
 mod util;
 
 use colored::Colorize;
diff --git a/src/metadata.rs b/src/metadata.rs
new file mode 100644
index 0000000..290a6c9
--- /dev/null
+++ b/src/metadata.rs
@@ -0,0 +1,61 @@
+//! Extended metadata for generated pak files.
+
+use std::io::{self, Read, Write};
+
+use ree_pak_core::{
+    filename::{FileNameExt, FileNameFull},
+    pak::PakArchive,
+    read::archive::PakArchiveReader,
+    write::{FileOptions, PakWriter},
+};
+use serde::{Deserialize, Serialize};
+
+const METADATA_KEY: &str = "__TEX_DECOMPRESSOR_METADATA__";
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct PakMetadata {
+    pub version: u32,
+    pub is_uncompressed_patch: bool,
+}
+
+impl PakMetadata {
+    pub fn from_pak_archive<R>(
+        reader: R,
+        pak_archive: &PakArchive,
+    ) -> color_eyre::Result<Option<Self>>
+    where
+        R: io::Read + io::Seek,
+    {
+        let key_name = FileNameFull::new(METADATA_KEY);
+        let entry = pak_archive
+            .entries()
+            .iter()
+            .find(|entry| entry.hash() == key_name.hash_mixed());
+
+        if let Some(entry) = entry {
+            // read file
+            let mut archive_reader = PakArchiveReader::new(reader, pak_archive);
+            let mut entry_reader = archive_reader.owned_entry_reader(entry.clone())?;
+            let mut buf = Vec::new();
+            entry_reader.read_to_end(&mut buf)?;
+
+            let metadata = serde_json::from_slice(&buf)?;
+            Ok(Some(metadata))
+        } else {
+            Ok(None)
+        }
+    }
+
+    pub fn write_to_pak<W>(&self, pak_writer: &mut PakWriter<W>) -> color_eyre::Result<()>
+    where
+        W: io::Write + io::Seek,
+    {
+        let json_str = serde_json::to_string(self)?;
+        let json_bytes = json_str.as_bytes();
+
+        pak_writer.start_file(METADATA_KEY, FileOptions::default())?;
+        pak_writer.write_all(json_bytes)?;
+
+        Ok(())
+    }
+}