diff --git a/genimtools/src/ailist/mod.rs b/genimtools/src/ailist/mod.rs
index 026ca0a3..7bc22e22 100644
--- a/genimtools/src/ailist/mod.rs
+++ b/genimtools/src/ailist/mod.rs
@@ -37,7 +37,7 @@ impl AIList {
 
             *intervals = results.3;
 
-            if intervals.len() == 0 {
+            if intervals.is_empty() {
                 break;
             } else {
                 header_list.push(starts.len());
@@ -53,7 +53,7 @@ impl AIList {
     }
 
     fn decompose(
-        intervals: &mut Vec<Interval>,
+        intervals: &mut [Interval],
         minimum_coverage_length: usize,
     ) -> (Vec<u32>, Vec<u32>, Vec<u32>, Vec<Interval>) {
         // look at the next minL*2 intervals
@@ -119,7 +119,7 @@ impl AIList {
                 })
             }
         }
-        return results_list;
+        results_list
     }
 
     pub fn query(&self, interval: &Interval) -> Vec<Interval> {
@@ -142,7 +142,7 @@ impl AIList {
             &self.max_ends[self.header_list[i]..],
         ));
 
-        return results_list;
+        results_list
     }
 
     pub fn print(&self) {
diff --git a/genimtools/src/common/models/tokenized_regionset.rs b/genimtools/src/common/models/tokenized_regionset.rs
index 5f97b97e..9246ca12 100644
--- a/genimtools/src/common/models/tokenized_regionset.rs
+++ b/genimtools/src/common/models/tokenized_regionset.rs
@@ -7,6 +7,7 @@ use crate::common::consts::{PAD_CHR, PAD_END, PAD_START};
 use crate::common::models::region::Region;
 use crate::common::models::tokenized_region::TokenizedRegion;
 use crate::common::models::universe::Universe;
+use crate::io::write_tokens_to_gtok;
 
 pub struct TokenizedRegionSet<'a> {
     pub regions: Vec<Region>,
@@ -72,14 +73,9 @@ impl<'a> TokenizedRegionSet<'a> {
     /// Write a TokenizedRegionSet to a .gtok file
     /// * `path` - A PathBuf to write the .gtok file to
     /// 
-    pub fn to_gtok_file(&self, path: &PathBuf) -> Result<(), Box<dyn Error>> {
-        let mut file = File::create(path)?;
-        for region in self.regions.iter() {
-            let id = self.universe.convert_region_to_id(region);
-            let line = format!("{}\n", id);
-            file.write_all(line.as_bytes())?;
-        }
-
+    pub fn to_gtok_file(&self, path: &str) -> Result<(), Box<dyn Error>> {
+        let tokens = self.to_region_ids();
+        write_tokens_to_gtok(path, &tokens)?;
         Ok(())
     }
 
diff --git a/genimtools/src/io/mod.rs b/genimtools/src/io/mod.rs
new file mode 100644
index 00000000..ea5afb5e
--- /dev/null
+++ b/genimtools/src/io/mod.rs
@@ -0,0 +1,39 @@
+use std::fs::File;
+use std::io::{Write, Read, BufReader, BufWriter};
+
+///
+/// Writes a vector of tokens to a file in the `.gtok` format.
+/// # Arguments
+/// - filename: the file to save the tokens to
+/// - tokens: tokens to save
+/// 
+pub fn write_tokens_to_gtok(filename: &str, tokens: &[u32]) -> std::io::Result<()> {
+    let file = File::create(filename)?;
+    let mut writer = BufWriter::new(file);
+
+    for &token in tokens {
+        writer.write_all(&token.to_le_bytes())?;
+    }
+
+    Ok(())
+}
+
+///
+/// Read in a vector of tokens from a file in the `.gtok` format.
+/// # Arguments
+/// - filename: filename to read the tokens from
+/// 
+/// # Returns
+/// - vector of tokens in u32 format
+pub fn read_tokens_from_gtok(filename: &str) -> std::io::Result<Vec<u32>> {
+    let file = File::open(filename)?;
+    let mut reader = BufReader::new(file);
+    let mut tokens = Vec::new();
+    let mut buffer = [0; 4];
+
+    while let Ok(()) = reader.read_exact(&mut buffer) {
+        tokens.push(u32::from_le_bytes(buffer));
+    }
+
+    Ok(tokens)
+}
\ No newline at end of file
diff --git a/genimtools/src/lib.rs b/genimtools/src/lib.rs
index 9129528e..71157319 100644
--- a/genimtools/src/lib.rs
+++ b/genimtools/src/lib.rs
@@ -9,4 +9,5 @@ pub mod common;
 pub mod tokenizers;
 pub mod uniwig;
 pub mod vocab;
-pub mod tools;
\ No newline at end of file
+pub mod tools;
+pub mod io;
\ No newline at end of file
diff --git a/genimtools/src/tools/cli.rs b/genimtools/src/tools/cli.rs
index d374dcfc..c8b8cb6d 100644
--- a/genimtools/src/tools/cli.rs
+++ b/genimtools/src/tools/cli.rs
@@ -34,7 +34,7 @@ pub fn make_tools_cli() -> Command {
 
 pub mod handlers {
     
-    use std::path::{Path, PathBuf};
+    use std::path::Path;
 
     use crate::{tokenizers::{self, Tokenizer}, common::models::RegionSet};
 
@@ -90,7 +90,7 @@ pub mod handlers {
                     match data {
                         Ok(data) => {
                             let result = tokenizer.tokenize_region_set(&data).expect("Data couldn't be tokenized.");
-                            let _ = result.to_gtok_file(&PathBuf::from(new_file));
+                            let _ = result.to_gtok_file(new_file.to_str().unwrap());
                         },
                         Err(e) => panic!("There was an error readig the data file: {}", e)
                     }