diff --git a/src/error.rs b/src/error.rs
new file mode 100644
index 0000000..a74d313
--- /dev/null
+++ b/src/error.rs
@@ -0,0 +1,31 @@
+use std::io;
+use std::path::PathBuf;
+
+#[derive(Debug)]
+pub enum CommitError {
+    NotADescendantOfCurrentDir(PathBuf),
+    InsideTourDir(PathBuf),
+    Io(io::Error),
+}
+
+impl std::fmt::Display for CommitError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::NotADescendantOfCurrentDir(path) => {
+                write!(f, "File {:?} is not a descendant of the working directory.", path)
+            }
+            Self::InsideTourDir(path) => {
+                write!(f, "File {:?} is inside a .tour directory, which is not allowed.", path)
+            }
+            Self::Io(e) => write!(f, "IO error: {}", e),
+        }
+    }
+}
+
+impl std::error::Error for CommitError {}
+
+impl From<io::Error> for CommitError {
+    fn from(e: io::Error) -> Self {
+        Self::Io(e)
+    }
+}