diff --git a/cli/args/flags.rs b/cli/args/flags.rs
index 02d30d055c..6aa1386064 100644
--- a/cli/args/flags.rs
+++ b/cli/args/flags.rs
@@ -2281,7 +2281,7 @@ Ignore formatting a file by adding an ignore comment at the top of the file:
           .value_parser([
             "ts", "tsx", "js", "jsx", "md", "json", "jsonc", "css", "scss",
             "sass", "less", "html", "svelte", "vue", "astro", "yml", "yaml",
-            "ipynb", "sql"
+            "ipynb", "sql", "vto", "njk"
           ])
           .help_heading(FMT_HEADING).requires("files"),
       )
diff --git a/tests/specs/fmt/njk/__test__.jsonc b/tests/specs/fmt/njk/__test__.jsonc
index 8b6bc87d47..9062a36079 100644
--- a/tests/specs/fmt/njk/__test__.jsonc
+++ b/tests/specs/fmt/njk/__test__.jsonc
@@ -1,5 +1,14 @@
 {
   "tempDir": true,
-  "args": "fmt --unstable-component",
-  "output": "[WILDLINE]badly_formatted.njk\nChecked 1 file\n"
-}
\ No newline at end of file
+  "steps": [
+    {
+      "args": "fmt --unstable-component",
+      "output": "[WILDLINE]badly_formatted.njk\nChecked 1 file\n"
+    },
+    {
+      "args": "fmt --unstable-component --ext=njk -",
+      "input": "<h1>  {{ \"Hello, world!\" |> toUpperCase }}\n  </h1>\n",
+      "output": "<h1>\n  {{ \"Hello, world!\" |> toUpperCase }}\n</h1>\n"
+    }
+  ]
+}
diff --git a/tests/specs/fmt/vento/__test__.jsonc b/tests/specs/fmt/vento/__test__.jsonc
index c3e3bbf7d1..a38036f455 100644
--- a/tests/specs/fmt/vento/__test__.jsonc
+++ b/tests/specs/fmt/vento/__test__.jsonc
@@ -1,5 +1,14 @@
 {
   "tempDir": true,
-  "args": "fmt --unstable-component",
-  "output": "[WILDLINE]badly_formatted.vto\nChecked 1 file\n"
-}
\ No newline at end of file
+  "steps": [
+    {
+      "args": "fmt --unstable-component",
+      "output": "[WILDLINE]badly_formatted.vto\nChecked 1 file\n"
+    },
+    {
+      "args": "fmt --unstable-component --ext=vto -",
+      "input": "<h1>  {{ \"Hello, world!\" |> upper }}\n  </h1>\n",
+      "output": "<h1>\n  {{ \"Hello, world!\" |> upper }}\n</h1>\n"
+    }
+  ]
+}