diff --git a/.prettierrc b/.prettierrc
new file mode 100644
index 0000000..8af31cd
--- /dev/null
+++ b/.prettierrc
@@ -0,0 +1,4 @@
+{
+    "tabWidth": 4,
+    "proseWrap": "always"
+}
diff --git a/TODO.md b/TODO.md
index ae65dff..aaa3187 100644
--- a/TODO.md
+++ b/TODO.md
@@ -20,6 +20,10 @@ main cannot regress.
 
 # Completed Steps
 
+- 2026-09-22: Added a root `.prettierrc` (`tabWidth: 4`,
+  `proseWrap: always`) pinning the project prettier settings, and
+  dropped the now-redundant inline `--tab-width 4` from `script/fmt` so
+  the config file is the single source of truth (#197).
 - 2026-09-22: Fixed the flaky `t.TempDir` cleanup race in
   `internal/service/webhook` by tracking the async deployment goroutine
   in a `sync.WaitGroup` and exposing `WaitForDeployments`; tests now
diff --git a/script/fmt b/script/fmt
index 2c9c55c..667cac5 100755
--- a/script/fmt
+++ b/script/fmt
@@ -8,7 +8,7 @@ main() {
     cd "$ROOT"
     gofmt -s -w .
     goimports -w .
-    npx prettier --write --tab-width 4 static/js/*.js
+    npx prettier --write static/js/*.js
 }
 
 main "$@"