diff --git a/.env.local.example b/.env.local.example
new file mode 100644
index 0000000..5624399
--- /dev/null
+++ b/.env.local.example
@@ -0,0 +1,10 @@
+# Copy to .env.local and replace placeholder values.
+AUTH_GOOGLE_ID=your-google-oauth-client-id
+AUTH_GOOGLE_SECRET=your-google-oauth-client-secret
+AUTH_SECRET=generate-with-openssl-rand-base64-32
+AUTH_URL=http://localhost:3000
+
+# Optional: set to false/0/no/off to disable saving new vocabulary rows.
+NEXT_PUBLIC_VOCAB_SAVING_ENABLED=true
+# Optional server-side override (if unset, NEXT_PUBLIC_VOCAB_SAVING_ENABLED is used).
+VOCAB_SAVING_ENABLED=true
diff --git a/.gitignore b/.gitignore
index 5ef6a52..b721bff 100644
--- a/.gitignore
+++ b/.gitignore
@@ -32,6 +32,7 @@ yarn-error.log*
 
 # env files (can opt-in for committing if needed)
 .env*
+!.env.local.example
 
 # vercel
 .vercel
diff --git a/.project/overview.md b/.project/overview.md
index 8ec2fe9..00da7be 100644
--- a/.project/overview.md
+++ b/.project/overview.md
@@ -27,7 +27,7 @@ translation and linguistic context as you read.
 
 ### [002-build-v2-mvp](goals/002-build-v2-mvp.md) — active
 <!-- - [google-oauth-flow](tasks/task-005_google-oauth-flow.md) — done 2026-06-13 -->
-- [google-sheets-adapter](tasks/task-006_google-sheets-adapter.md) — in-progress
+- [google-sheets-adapter](tasks/task-006_google-sheets-adapter.md) — in-review
 - [oauth-token-refresh](tasks/task-007_oauth-token-refresh.md) — to-do
 - [vocab-sheet-connect-ux](tasks/task-008_vocab-sheet-connect-ux.md) — to-do
 - [save-failure-notifications](tasks/task-009_save-failure-notifications.md) — to-do
diff --git a/.project/tasks/task-006_google-sheets-adapter.md b/.project/tasks/task-006_google-sheets-adapter.md
index 9444ca4..45d4563 100644
--- a/.project/tasks/task-006_google-sheets-adapter.md
+++ b/.project/tasks/task-006_google-sheets-adapter.md
@@ -1,5 +1,5 @@
 ---
-status: in-progress
+status: in-review
 owner: both
 goal: "[[002-build-v2-mvp]]"
 ---
@@ -26,7 +26,7 @@ interfaces are already in place — this task designs the sheet and builds the a
       via `x-vocab-sheet-id` header) → adapter. Sheet chosen via "Vocab sheet" field in nav.
 - [x] Verify: sign in → save a word while reading → open Google Sheet → row appears.
       Confirmed live by [human] 2026-06-13.
-- [ ] Add an env flag to enable/disable saving (default on), so the user can read without
+- [x] Add an env flag to enable/disable saving (default on), so the user can read without
       writing to the sheet. (Impl detail: client `NEXT_PUBLIC_*` vs server-side gate — decide
       when building.)
 
@@ -68,6 +68,9 @@ A word saved while reading shows up as a row in the user's Google Sheet.
 - 2026-06-13: Reopened (in-review → in-progress) to add an env on/off toggle for saving
   [human request]. The core sheet-save flow stays verified; only the toggle is outstanding.
   Sheet-connect UX + validation split to [[task-008_vocab-sheet-connect-ux]].
+- 2026-06-13: Added env save-toggle (`NEXT_PUBLIC_VOCAB_SAVING_ENABLED`, optional server
+  override `VOCAB_SAVING_ENABLED`) with default-on behavior. When disabled, client skips
+  save requests and server POST short-circuits safely.
 
 ### ⏸ PARKED 2026-06-13 — resume here (next agent, read this first)
 - **Only remaining step in this task:** the env on/off toggle for saving (see Steps). The
diff --git a/README.md b/README.md
index 0b12033..929cbe4 100644
--- a/README.md
+++ b/README.md
@@ -26,11 +26,17 @@ A personal Finnish learning app — read Finnish text with interactive word-by-w
 
 ```bash
 npm install
+cp .env.local.example .env.local
 npm run dev
 ```
 
 Open [http://localhost:3000](http://localhost:3000).
 
+### Environment
+
+- `NEXT_PUBLIC_VOCAB_SAVING_ENABLED` (default: `true`) — build-time client flag; set `false`/`0`/`no`/`off` to read without writing new vocabulary rows (requires rebuilding when changed).
+- `VOCAB_SAVING_ENABLED` (optional server override) — runtime server flag with the same values; useful to force-disable POST saves without relying on a client rebuild.
+
 ### Build for Production
 
 ```bash
diff --git a/src/app/api/vocab/route.ts b/src/app/api/vocab/route.ts
index c3d3e4c..dd9bdeb 100644
--- a/src/app/api/vocab/route.ts
+++ b/src/app/api/vocab/route.ts
@@ -1,6 +1,7 @@
 import { NextResponse } from 'next/server';
 import { auth } from '@/lib/auth';
 import { createGoogleSheetsVocabRepository } from '@/modules/vocab-store/adapters/GoogleSheetsVocabRepository';
+import { isServerVocabSavingEnabled } from '@/modules/vocab-store/vocabSavingFlag';
 
 const SHEET_ID_HEADER = 'x-vocab-sheet-id';
 
@@ -19,6 +20,10 @@ export async function POST(request: Request) {
   const session = await auth();
   if (!session) return NextResponse.json({ error: 'Not authenticated' }, { status: 401 });
 
+  if (!isServerVocabSavingEnabled()) {
+    return NextResponse.json({ ok: true, skipped: 'disabled' });
+  }
+
   const sheetId = request.headers.get(SHEET_ID_HEADER);
   if (!sheetId) return NextResponse.json({ error: 'No vocabulary sheet configured' }, { status: 400 });
 
diff --git a/src/modules/vocab-store/saveVocab.ts b/src/modules/vocab-store/saveVocab.ts
index 4191489..d1fddaa 100644
--- a/src/modules/vocab-store/saveVocab.ts
+++ b/src/modules/vocab-store/saveVocab.ts
@@ -1,4 +1,5 @@
 import { getVocabSheetId } from './sheetSettings';
+import { isClientVocabSavingEnabled } from './vocabSavingFlag';
 
 const SHEET_ID_HEADER = 'x-vocab-sheet-id';
 
@@ -8,6 +9,8 @@ export async function saveVocab(
   sourceLang: string,
   targetLang: string,
 ): Promise<void> {
+  if (!isClientVocabSavingEnabled()) return;
+
   const sheetId = getVocabSheetId();
   // No sheet configured yet — nothing to save to. Reading is unaffected.
   if (!sheetId) return;
diff --git a/src/modules/vocab-store/vocabSavingFlag.ts b/src/modules/vocab-store/vocabSavingFlag.ts
new file mode 100644
index 0000000..c7ec83f
--- /dev/null
+++ b/src/modules/vocab-store/vocabSavingFlag.ts
@@ -0,0 +1,13 @@
+const FALSE_ENV_VALUES = new Set(['0', 'false', 'no', 'off']);
+
+const isEnabled = (value: string | undefined): boolean => {
+  // Default-on behavior: missing env values keep vocabulary saving enabled.
+  if (!value) return true;
+  return !FALSE_ENV_VALUES.has(value.trim().toLowerCase());
+};
+
+export const isClientVocabSavingEnabled = (): boolean =>
+  isEnabled(process.env.NEXT_PUBLIC_VOCAB_SAVING_ENABLED);
+
+export const isServerVocabSavingEnabled = (): boolean =>
+  isEnabled(process.env.VOCAB_SAVING_ENABLED ?? process.env.NEXT_PUBLIC_VOCAB_SAVING_ENABLED);