diff --git a/README.md b/README.md
index 765d8ae..4f497ce 100644
--- a/README.md
+++ b/README.md
@@ -181,6 +181,19 @@ pkgs.mkNginxServer {
 }
 ```
 
+### [`gitSource`](./lib/git-source)
+
+for development package nix files, computes the source set of files tracked by git at the given root
+path
+
+example:
+```nix
+stdenv.mkDerivation {
+  # ...
+  src = gitSource { root = ./.; };
+}
+```
+
 ## development
 
 structure of this repo
diff --git a/default.nix b/default.nix
index dbb718a..8a63b62 100644
--- a/default.nix
+++ b/default.nix
@@ -9,6 +9,8 @@
     (final: prev: {
       fetchFromSteam = prev.callPackage ./lib/fetchsteam {};
 
+      gitSource = prev.callPackage ./lib/git-source {};
+
       ghidra_headless = prev.ghidra.override {
         openjdk17 = prev.openjdk17_headless;
       };
diff --git a/lib/git-source/default.nix b/lib/git-source/default.nix
new file mode 100644
index 0000000..9ed4f6f
--- /dev/null
+++ b/lib/git-source/default.nix
@@ -0,0 +1,8 @@
+{ lib }: { root }:
+let
+  fs = lib.fileset;
+  sourceFiles = fs.difference
+    (fs.gitTracked root)
+    (fs.fileFilter (file: file.hasExt "nix") root);
+in
+  fs.toSource { inherit root; fileset = sourceFiles; }