diff --git a/src/project.rs b/src/project.rs
index 220b9e35..bde4ac14 100644
--- a/src/project.rs
+++ b/src/project.rs
@@ -16,7 +16,8 @@ use crate::{
 };
 
 /// Represents 'default' project names that act as `init` files
-pub static DEFAULT_PROJECT_NAMES: [&str; 1] = ["default.project.json5"];
+/// Includes legacy `.json` extension as fallback for backwards compatibility.
+pub static DEFAULT_PROJECT_NAMES: [&str; 2] = ["default.project.json5", "default.project.json"];
 
 /// Error type returned by any function that handles projects.
 #[derive(Debug, Error)]
@@ -140,7 +141,7 @@ impl Project {
     pub fn is_project_file(path: &Path) -> bool {
         path.file_name()
             .and_then(|name| name.to_str())
-            .map(|name| name.ends_with(".project.json5"))
+            .map(|name| name.ends_with(".project.json5") || name.ends_with(".project.json"))
             .unwrap_or(false)
     }
 
diff --git a/src/snapshot_middleware/dir.rs b/src/snapshot_middleware/dir.rs
index c610824e..ab541014 100644
--- a/src/snapshot_middleware/dir.rs
+++ b/src/snapshot_middleware/dir.rs
@@ -68,12 +68,17 @@ pub fn snapshot_dir_no_meta(
         // TODO: We shouldn't need to know about Lua existing in this
         // middleware. Should we figure out a way for that function to add
         // relevant paths to this middleware?
+        // Modern extensions (preferred)
         normalized_path.join("init.luau"),
         normalized_path.join("init.server.luau"),
         normalized_path.join("init.client.luau"),
         normalized_path.join("init.local.luau"),
         normalized_path.join("init.legacy.luau"),
         normalized_path.join("init.csv"),
+        // Legacy extensions (for backwards compatibility)
+        normalized_path.join("init.lua"),
+        normalized_path.join("init.server.lua"),
+        normalized_path.join("init.client.lua"),
     ];
 
     let snapshot = InstanceSnapshot::new()
diff --git a/src/snapshot_middleware/meta_file.rs b/src/snapshot_middleware/meta_file.rs
index b60dbf9a..d69798e0 100644
--- a/src/snapshot_middleware/meta_file.rs
+++ b/src/snapshot_middleware/meta_file.rs
@@ -64,15 +64,22 @@ impl AdjacentMetadata {
             .or_else(|| file_stem.strip_suffix(".local"))
             .or_else(|| file_stem.strip_suffix(".legacy"))
             .unwrap_or(file_stem);
-        let meta_path = path.with_file_name(format!("{base_name}.meta.json5"));
+        
+        // Try modern extension first, then fall back to legacy
+        let meta_path_json5 = path.with_file_name(format!("{base_name}.meta.json5"));
+        let meta_path_json = path.with_file_name(format!("{base_name}.meta.json"));
 
-        if let Some(meta_contents) = vfs.read(&meta_path).with_not_found()? {
-            let mut metadata = Self::from_slice(&meta_contents, meta_path.clone())?;
+        if let Some(meta_contents) = vfs.read(&meta_path_json5).with_not_found()? {
+            let mut metadata = Self::from_slice(&meta_contents, meta_path_json5.clone())?;
+            metadata.apply_all(snapshot)?;
+        } else if let Some(meta_contents) = vfs.read(&meta_path_json).with_not_found()? {
+            // Legacy fallback: .meta.json
+            let mut metadata = Self::from_slice(&meta_contents, meta_path_json.clone())?;
             metadata.apply_all(snapshot)?;
         }
 
         // Rather than pushing these in the snapshot middleware, we can just do it here.
-        snapshot.metadata.relevant_paths.push(meta_path);
+        snapshot.metadata.relevant_paths.push(meta_path_json5);
 
         Ok(())
     }
@@ -282,15 +289,21 @@ impl DirectoryMetadata {
         path: &Path,
         snapshot: &mut InstanceSnapshot,
     ) -> anyhow::Result<()> {
-        let meta_path = path.join("init.meta.json5");
+        // Try modern extension first, then fall back to legacy
+        let meta_path_json5 = path.join("init.meta.json5");
+        let meta_path_json = path.join("init.meta.json");
 
-        if let Some(meta_contents) = vfs.read(&meta_path).with_not_found()? {
-            let mut metadata = Self::from_slice(&meta_contents, meta_path.clone())?;
+        if let Some(meta_contents) = vfs.read(&meta_path_json5).with_not_found()? {
+            let mut metadata = Self::from_slice(&meta_contents, meta_path_json5.clone())?;
+            metadata.apply_all(snapshot)?;
+        } else if let Some(meta_contents) = vfs.read(&meta_path_json).with_not_found()? {
+            // Legacy fallback: init.meta.json
+            let mut metadata = Self::from_slice(&meta_contents, meta_path_json.clone())?;
             metadata.apply_all(snapshot)?;
         }
 
         // Rather than pushing these in the snapshot middleware, we can just do it here.
-        snapshot.metadata.relevant_paths.push(meta_path);
+        snapshot.metadata.relevant_paths.push(meta_path_json5);
 
         Ok(())
     }
@@ -484,11 +497,20 @@ impl DirectoryMetadata {
 /// Retrieves the meta file that should be applied for the provided directory,
 /// if it exists.
 pub fn dir_meta(vfs: &Vfs, path: &Path) -> anyhow::Result<Option<DirectoryMetadata>> {
-    let meta_path = path.join("init.meta.json5");
-    if let Some(meta_contents) = vfs.read(&meta_path).with_not_found()? {
-        let metadata = DirectoryMetadata::from_slice(&meta_contents, meta_path)?;
+    // Try modern extension first, then fall back to legacy
+    let meta_path_json5 = path.join("init.meta.json5");
+    if let Some(meta_contents) = vfs.read(&meta_path_json5).with_not_found()? {
+        let metadata = DirectoryMetadata::from_slice(&meta_contents, meta_path_json5)?;
         return Ok(Some(metadata));
     }
+    
+    // Legacy fallback: init.meta.json
+    let meta_path_json = path.join("init.meta.json");
+    if let Some(meta_contents) = vfs.read(&meta_path_json).with_not_found()? {
+        let metadata = DirectoryMetadata::from_slice(&meta_contents, meta_path_json)?;
+        return Ok(Some(metadata));
+    }
+    
     Ok(None)
 }
 
@@ -497,12 +519,22 @@ pub fn dir_meta(vfs: &Vfs, path: &Path) -> anyhow::Result<Option<DirectoryMetada
 ///
 /// The `name` field should be the name the metadata should have.
 pub fn file_meta(vfs: &Vfs, path: &Path, name: &str) -> anyhow::Result<Option<AdjacentMetadata>> {
-    let mut meta_path = path.with_file_name(name);
-    meta_path.set_extension("meta.json5");
-    if let Some(meta_contents) = vfs.read(&meta_path).with_not_found()? {
-        let metadata = AdjacentMetadata::from_slice(&meta_contents, meta_path)?;
+    // Try modern extension first, then fall back to legacy
+    let mut meta_path_json5 = path.with_file_name(name);
+    meta_path_json5.set_extension("meta.json5");
+    if let Some(meta_contents) = vfs.read(&meta_path_json5).with_not_found()? {
+        let metadata = AdjacentMetadata::from_slice(&meta_contents, meta_path_json5)?;
         return Ok(Some(metadata));
     }
+    
+    // Legacy fallback: .meta.json
+    let mut meta_path_json = path.with_file_name(name);
+    meta_path_json.set_extension("meta.json");
+    if let Some(meta_contents) = vfs.read(&meta_path_json).with_not_found()? {
+        let metadata = AdjacentMetadata::from_slice(&meta_contents, meta_path_json)?;
+        return Ok(Some(metadata));
+    }
+    
     Ok(None)
 }
 
diff --git a/src/snapshot_middleware/mod.rs b/src/snapshot_middleware/mod.rs
index 3208bb05..6a0ab917 100644
--- a/src/snapshot_middleware/mod.rs
+++ b/src/snapshot_middleware/mod.rs
@@ -94,8 +94,11 @@ pub fn snapshot_from_vfs(
 
         // TODO: Is this even necessary anymore?
         match file_name {
+            // Modern extensions
             "init.server.luau" | "init.client.luau" | "init.local.luau" | "init.legacy.luau"
-            | "init.luau" | "init.csv" => return Ok(None),
+            | "init.luau" | "init.csv" |
+            // Legacy extensions (for backwards compatibility)
+            "init.server.lua" | "init.client.lua" | "init.lua" => return Ok(None),
             _ => {}
         }
 
@@ -122,12 +125,17 @@ fn get_dir_middleware<'path>(
     static INIT_PATHS: OnceLock<Vec<(Middleware, &str)>> = OnceLock::new();
     let order = INIT_PATHS.get_or_init(|| {
         vec![
+            // Modern extensions (preferred)
             (Middleware::ModuleScriptDir, "init.luau"),
             (Middleware::ServerScriptDir, "init.server.luau"),
             (Middleware::ClientScriptDir, "init.client.luau"),
             (Middleware::LocalScriptDir, "init.local.luau"),
             (Middleware::LegacyScriptDir, "init.legacy.luau"),
             (Middleware::CsvDir, "init.csv"),
+            // Legacy extensions (for backwards compatibility)
+            (Middleware::ModuleScriptDir, "init.lua"),
+            (Middleware::ServerScriptDir, "init.server.lua"),
+            (Middleware::ClientScriptDir, "init.client.lua"),
         ]
     });
 
@@ -412,6 +420,7 @@ pub fn default_sync_rules() -> &'static [SyncRule] {
 
     DEFAULT_SYNC_RULES.get_or_init(|| {
         vec![
+            // Modern extensions (preferred)
             sync_rule!("*.server.luau", ServerScript, ".server.luau"),
             sync_rule!("*.client.luau", ClientScript, ".client.luau"),
             sync_rule!("*.plugin.luau", PluginScript, ".plugin.luau"),
@@ -421,6 +430,15 @@ pub fn default_sync_rules() -> &'static [SyncRule] {
             sync_rule!("*.project.json5", Project, ".project.json5"),
             sync_rule!("*.model.json5", JsonModel, ".model.json5"),
             sync_rule!("*.json5", Json, ".json5", "*.meta.json5"),
+            // Legacy Lua extensions (for backwards compatibility)
+            sync_rule!("*.server.lua", ServerScript, ".server.lua"),
+            sync_rule!("*.client.lua", ClientScript, ".client.lua"),
+            sync_rule!("*.lua", ModuleScript),
+            // Legacy JSON extensions (for backwards compatibility)
+            sync_rule!("*.project.json", Project, ".project.json"),
+            sync_rule!("*.model.json", JsonModel, ".model.json"),
+            sync_rule!("*.json", Json, ".json", "*.meta.json"),
+            // Other formats
             sync_rule!("*.toml", Toml),
             sync_rule!("*.csv", Csv),
             sync_rule!("*.txt", Text),
diff --git a/src/snapshot_middleware/snapshots/librojo__snapshot_middleware__csv__test__csv_init.snap b/src/snapshot_middleware/snapshots/librojo__snapshot_middleware__csv__test__csv_init.snap
index 99156828..4a178832 100644
--- a/src/snapshot_middleware/snapshots/librojo__snapshot_middleware__csv__test__csv_init.snap
+++ b/src/snapshot_middleware/snapshots/librojo__snapshot_middleware__csv__test__csv_init.snap
@@ -15,6 +15,9 @@ metadata:
     - /root/init.local.luau
     - /root/init.legacy.luau
     - /root/init.csv
+    - /root/init.lua
+    - /root/init.server.lua
+    - /root/init.client.lua
     - /root/init.meta.json5
   context:
     decode_windows_invalid_chars: true
diff --git a/src/snapshot_middleware/snapshots/librojo__snapshot_middleware__csv__test__csv_init_with_meta.snap b/src/snapshot_middleware/snapshots/librojo__snapshot_middleware__csv__test__csv_init_with_meta.snap
index 1a0ac9e3..85e790a2 100644
--- a/src/snapshot_middleware/snapshots/librojo__snapshot_middleware__csv__test__csv_init_with_meta.snap
+++ b/src/snapshot_middleware/snapshots/librojo__snapshot_middleware__csv__test__csv_init_with_meta.snap
@@ -15,6 +15,9 @@ metadata:
     - /root/init.local.luau
     - /root/init.legacy.luau
     - /root/init.csv
+    - /root/init.lua
+    - /root/init.server.lua
+    - /root/init.client.lua
     - /root/init.meta.json5
   context:
     decode_windows_invalid_chars: true
diff --git a/src/snapshot_middleware/snapshots/librojo__snapshot_middleware__dir__test__empty_folder.snap b/src/snapshot_middleware/snapshots/librojo__snapshot_middleware__dir__test__empty_folder.snap
index c0fcbbd8..f1c96a44 100644
--- a/src/snapshot_middleware/snapshots/librojo__snapshot_middleware__dir__test__empty_folder.snap
+++ b/src/snapshot_middleware/snapshots/librojo__snapshot_middleware__dir__test__empty_folder.snap
@@ -15,6 +15,9 @@ metadata:
     - /foo/init.local.luau
     - /foo/init.legacy.luau
     - /foo/init.csv
+    - /foo/init.lua
+    - /foo/init.server.lua
+    - /foo/init.client.lua
     - /foo/init.meta.json5
   context:
     decode_windows_invalid_chars: true
diff --git a/src/snapshot_middleware/snapshots/librojo__snapshot_middleware__dir__test__folder_in_folder.snap b/src/snapshot_middleware/snapshots/librojo__snapshot_middleware__dir__test__folder_in_folder.snap
index ee21a41a..52ca0c33 100644
--- a/src/snapshot_middleware/snapshots/librojo__snapshot_middleware__dir__test__folder_in_folder.snap
+++ b/src/snapshot_middleware/snapshots/librojo__snapshot_middleware__dir__test__folder_in_folder.snap
@@ -15,6 +15,9 @@ metadata:
     - /foo/init.local.luau
     - /foo/init.legacy.luau
     - /foo/init.csv
+    - /foo/init.lua
+    - /foo/init.server.lua
+    - /foo/init.client.lua
     - /foo/init.meta.json5
   context:
     decode_windows_invalid_chars: true
@@ -38,6 +41,9 @@ children:
         - /foo/Child/init.local.luau
         - /foo/Child/init.legacy.luau
         - /foo/Child/init.csv
+        - /foo/Child/init.lua
+        - /foo/Child/init.server.lua
+        - /foo/Child/init.client.lua
         - /foo/Child/init.meta.json5
       context:
         decode_windows_invalid_chars: true
diff --git a/src/snapshot_middleware/snapshots/librojo__snapshot_middleware__lua__test__init_module_from_vfs.snap b/src/snapshot_middleware/snapshots/librojo__snapshot_middleware__lua__test__init_module_from_vfs.snap
index 29cc22c0..3178e91f 100644
--- a/src/snapshot_middleware/snapshots/librojo__snapshot_middleware__lua__test__init_module_from_vfs.snap
+++ b/src/snapshot_middleware/snapshots/librojo__snapshot_middleware__lua__test__init_module_from_vfs.snap
@@ -15,6 +15,9 @@ metadata:
     - /root/init.local.luau
     - /root/init.legacy.luau
     - /root/init.csv
+    - /root/init.lua
+    - /root/init.server.lua
+    - /root/init.client.lua
     - /root/init.meta.json5
   context:
     decode_windows_invalid_chars: true
diff --git a/src/snapshot_middleware/snapshots/librojo__snapshot_middleware__lua__test__init_module_from_vfs_with_meta.snap b/src/snapshot_middleware/snapshots/librojo__snapshot_middleware__lua__test__init_module_from_vfs_with_meta.snap
index 1645dca6..38364335 100644
--- a/src/snapshot_middleware/snapshots/librojo__snapshot_middleware__lua__test__init_module_from_vfs_with_meta.snap
+++ b/src/snapshot_middleware/snapshots/librojo__snapshot_middleware__lua__test__init_module_from_vfs_with_meta.snap
@@ -15,6 +15,9 @@ metadata:
     - /root/init.local.luau
     - /root/init.legacy.luau
     - /root/init.csv
+    - /root/init.lua
+    - /root/init.server.lua
+    - /root/init.client.lua
     - /root/init.meta.json5
   context:
     decode_windows_invalid_chars: true