diff --git a/.env.example b/.env.example
index 121dff4..5283179 100644
--- a/.env.example
+++ b/.env.example
@@ -3,8 +3,10 @@ POSTGRES_PASSWORD=lyra
 POSTGRES_DB=lyra
 DATABASE_URL=postgresql://lyra:lyra@db:5432/lyra
 
-# 32 random bytes, base64. Generate with: openssl rand -base64 32
-LYRA_SECRET_KEY=MDEyMzQ1Njc4OWFiY2RlZjAxMjM0NTY3ODlhYmNkZWY=
+# Encryption key for stored credentials — 32 random bytes, base64. YOU MUST REPLACE THIS.
+# Generate your own:  openssl rand -base64 32
+# Leaving the placeholder (or an empty key) makes web + worker refuse to start.
+LYRA_SECRET_KEY=CHANGE_ME_generate_with_openssl_rand_base64_32
 
 # Shared password protecting the whole web UI + API. When set, every request must sign in
 # (one shared password, no per-user accounts). LEAVE UNSET AND THE APP IS OPEN to anyone
diff --git a/README.md b/README.md
index ea98ea1..dc8dfaa 100644
--- a/README.md
+++ b/README.md
@@ -90,6 +90,13 @@ cp .env.example .env          # then edit: set LYRA_SECRET_KEY (openssl rand -ba
 docker compose up -d --build  # web on http://localhost:8770 ; NEVER `down -v` (wipes the Postgres volume)
 ```
 
+**Generate your own `LYRA_SECRET_KEY`** (`openssl rand -base64 32`) before first run — it
+encrypts your stored Qobuz/Soulseek/Last.fm credentials. `.env.example` ships an obvious
+placeholder, and both web and worker **refuse to start** while the key is missing or still
+the placeholder. Once set, keep it stable: changing it makes already-stored credentials
+undecryptable (you'd re-enter them in Settings). Optionally set `LYRA_PASSWORD` too (see
+[Security](#security)).
+
 The web entrypoint runs `prisma migrate deploy` on every rebuild, so schema changes
 reach the live DB automatically. Enter Qobuz / Soulseek / Last.fm credentials in
 **Settings** (they persist across rebuilds), then follow an artist or request an album
diff --git a/web/src/instrumentation.ts b/web/src/instrumentation.ts
new file mode 100644
index 0000000..4aec695
--- /dev/null
+++ b/web/src/instrumentation.ts
@@ -0,0 +1,21 @@
+// Runs once on server startup (Next.js instrumentation hook). Fail fast (or warn loudly)
+// on a missing/placeholder/public LYRA_SECRET_KEY so a publicly-known key can't silently
+// encrypt every credential.
+import { secretKeyProblem } from "@/lib/secret-key";
+
+export async function register() {
+  if (process.env.NEXT_RUNTIME !== "nodejs") return; // check once, in the Node runtime
+  const problem = secretKeyProblem();
+  if (!problem) return;
+
+  const banner = "=".repeat(72);
+  if (problem.fatal) {
+    console.error(
+      `\n${banner}\nFATAL: ${problem.message}.\n` +
+        `Generate one:  openssl rand -base64 32\n` +
+        `Then set LYRA_SECRET_KEY in your .env and restart.\n${banner}\n`,
+    );
+    throw new Error(problem.message); // fail fast
+  }
+  console.warn(`\n${banner}\nWARNING: ${problem.message}.\n${banner}\n`);
+}
diff --git a/web/src/lib/crypto.ts b/web/src/lib/crypto.ts
index 1670ff4..76039bc 100644
--- a/web/src/lib/crypto.ts
+++ b/web/src/lib/crypto.ts
@@ -1,5 +1,9 @@
 import { createCipheriv, createDecipheriv, randomBytes } from "node:crypto";
 
+// Re-exported for existing callers; the checks live in an edge-safe module (secret-key.ts)
+// so the instrumentation hook can import them without pulling in node:crypto.
+export { secretKeyProblem, PLACEHOLDER_SECRET_KEY } from "./secret-key";
+
 function key(): Buffer {
   const b64 = process.env.LYRA_SECRET_KEY;
   if (!b64) throw new Error("LYRA_SECRET_KEY is not set");
diff --git a/web/src/lib/secret-key.test.ts b/web/src/lib/secret-key.test.ts
new file mode 100644
index 0000000..133bc6e
--- /dev/null
+++ b/web/src/lib/secret-key.test.ts
@@ -0,0 +1,41 @@
+import { describe, it, expect, afterEach } from "vitest";
+import { secretKeyProblem, PLACEHOLDER_SECRET_KEY } from "./secret-key";
+
+const GOOD = Buffer.from("x".repeat(32)).toString("base64");
+const LEGACY = "MDEyMzQ1Njc4OWFiY2RlZjAxMjM0NTY3ODlhYmNkZWY=";
+const original = process.env.LYRA_SECRET_KEY;
+
+afterEach(() => {
+  if (original === undefined) delete process.env.LYRA_SECRET_KEY;
+  else process.env.LYRA_SECRET_KEY = original;
+});
+
+describe("secretKeyProblem", () => {
+  it("is fatal when missing", () => {
+    delete process.env.LYRA_SECRET_KEY;
+    expect(secretKeyProblem()).toEqual({ message: "LYRA_SECRET_KEY is not set", fatal: true });
+  });
+
+  it("is fatal on the placeholder", () => {
+    process.env.LYRA_SECRET_KEY = PLACEHOLDER_SECRET_KEY;
+    expect(secretKeyProblem()?.fatal).toBe(true);
+  });
+
+  it("is fatal on wrong length", () => {
+    process.env.LYRA_SECRET_KEY = Buffer.from("short").toString("base64");
+    expect(secretKeyProblem()).toMatchObject({ fatal: true });
+    expect(secretKeyProblem()?.message).toContain("32 bytes");
+  });
+
+  it("warns (not fatal) on the old public key", () => {
+    process.env.LYRA_SECRET_KEY = LEGACY;
+    const p = secretKeyProblem();
+    expect(p?.fatal).toBe(false);
+    expect(p?.message).toContain("PUBLIC");
+  });
+
+  it("accepts a proper key", () => {
+    process.env.LYRA_SECRET_KEY = GOOD;
+    expect(secretKeyProblem()).toBeNull();
+  });
+});
diff --git a/web/src/lib/secret-key.ts b/web/src/lib/secret-key.ts
new file mode 100644
index 0000000..49a3f39
--- /dev/null
+++ b/web/src/lib/secret-key.ts
@@ -0,0 +1,33 @@
+// Edge-safe LYRA_SECRET_KEY validation (no node:crypto / Buffer), so the Next.js
+// instrumentation hook — which is bundled for both the Node and Edge runtimes — can import
+// it. crypto.ts re-exports these for its own callers.
+
+// The obvious placeholder shipped in .env.example — must be replaced with a real key.
+export const PLACEHOLDER_SECRET_KEY = "CHANGE_ME_generate_with_openssl_rand_base64_32";
+// The valid-but-PUBLIC key git used to ship in .env.example. Warn (don't hard-fail): an
+// existing install may have encrypted its credentials under it.
+const LEGACY_PUBLIC_KEY = "MDEyMzQ1Njc4OWFiY2RlZjAxMjM0NTY3ODlhYmNkZWY=";
+
+/** Describe an unusable/insecure LYRA_SECRET_KEY, or null if it's fine. Used at startup. */
+export function secretKeyProblem(): { message: string; fatal: boolean } | null {
+  const b64 = process.env.LYRA_SECRET_KEY;
+  if (!b64) return { message: "LYRA_SECRET_KEY is not set", fatal: true };
+  if (b64 === PLACEHOLDER_SECRET_KEY)
+    return { message: "LYRA_SECRET_KEY is still the .env.example placeholder", fatal: true };
+  let byteLen: number;
+  try {
+    byteLen = atob(b64).length;
+  } catch {
+    return { message: "LYRA_SECRET_KEY is not valid base64", fatal: true };
+  }
+  if (byteLen !== 32)
+    return { message: "LYRA_SECRET_KEY must decode to 32 bytes", fatal: true };
+  if (b64 === LEGACY_PUBLIC_KEY)
+    return {
+      message:
+        "LYRA_SECRET_KEY is the old PUBLIC example key that shipped in git — anyone can " +
+        "decrypt your stored credentials; generate a fresh key and re-enter them",
+      fatal: false,
+    };
+  return null;
+}
diff --git a/worker/lyra_worker/crypto.py b/worker/lyra_worker/crypto.py
index 7a9dd13..c9a2059 100644
--- a/worker/lyra_worker/crypto.py
+++ b/worker/lyra_worker/crypto.py
@@ -4,6 +4,36 @@ import os
 
 from cryptography.hazmat.primitives.ciphers.aead import AESGCM
 
+# The obvious placeholder shipped in .env.example — must be replaced with a real key.
+PLACEHOLDER_SECRET_KEY = "CHANGE_ME_generate_with_openssl_rand_base64_32"
+# The valid-but-PUBLIC key git used to ship in .env.example. Anyone can decrypt creds
+# encrypted with it, so warn — but don't hard-fail, since an existing install may have
+# encrypted its credentials under it and hard-failing would brick it mid-flight.
+_LEGACY_PUBLIC_KEY = "MDEyMzQ1Njc4OWFiY2RlZjAxMjM0NTY3ODlhYmNkZWY="
+
+
+def secret_key_problem() -> tuple[str, bool] | None:
+    """Return (message, fatal) if LYRA_SECRET_KEY is unusable or insecure, else None.
+    fatal=True ⇒ the app should refuse to start; fatal=False ⇒ start but warn loudly."""
+    b64 = os.environ.get("LYRA_SECRET_KEY")
+    if not b64:
+        return ("LYRA_SECRET_KEY is not set", True)
+    if b64 == PLACEHOLDER_SECRET_KEY:
+        return ("LYRA_SECRET_KEY is still the .env.example placeholder", True)
+    try:
+        k = base64.b64decode(b64)
+    except Exception:
+        return ("LYRA_SECRET_KEY is not valid base64", True)
+    if len(k) != 32:
+        return ("LYRA_SECRET_KEY must decode to 32 bytes", True)
+    if b64 == _LEGACY_PUBLIC_KEY:
+        return (
+            "LYRA_SECRET_KEY is the old PUBLIC example key that shipped in git — anyone "
+            "can decrypt your stored credentials; generate a fresh key and re-enter them",
+            False,
+        )
+    return None
+
 
 def _key() -> bytes:
     b64 = os.environ.get("LYRA_SECRET_KEY")
diff --git a/worker/lyra_worker/main.py b/worker/lyra_worker/main.py
index 819f258..0ca0d5d 100644
--- a/worker/lyra_worker/main.py
+++ b/worker/lyra_worker/main.py
@@ -1,4 +1,5 @@
 import os
+import sys
 import time
 import uuid
 
@@ -6,6 +7,7 @@ import psycopg
 
 from lyra_worker.claim import claim_next
 from lyra_worker.config import get_config
+from lyra_worker.crypto import secret_key_problem
 from lyra_worker.db import wait_for_db
 from lyra_worker.discovery import DiscoveryConfig, DiscoveryResult, run_discovery
 from lyra_worker.library import clear_staging_root
@@ -165,7 +167,26 @@ def maybe_run_discovery(conn, sources, browser, config, dcfg, now, last_discover
     return now if due else last_discover_tick
 
 
+def _require_secret_key() -> None:
+    """Fail fast (or warn loudly) on a missing/placeholder/public LYRA_SECRET_KEY before
+    the worker touches any encrypted credential."""
+    problem = secret_key_problem()
+    if problem is None:
+        return
+    msg, fatal = problem
+    banner = "=" * 72
+    if fatal:
+        print(
+            f"\n{banner}\nFATAL: {msg}.\nGenerate one:  openssl rand -base64 32\n"
+            f"Then set LYRA_SECRET_KEY in your .env and restart.\n{banner}\n",
+            flush=True,
+        )
+        sys.exit(1)
+    print(f"\n{banner}\nWARNING: {msg}.\n{banner}\n", flush=True)
+
+
 def run_forever() -> None:
+    _require_secret_key()
     conn = wait_for_db()
     clear_staging_root(STAGING_ROOT)  # sweep any staging dirs orphaned by a prior crash
     adapters = build_adapters(get_config(conn))
diff --git a/worker/tests/test_secret_key.py b/worker/tests/test_secret_key.py
new file mode 100644
index 0000000..48c272f
--- /dev/null
+++ b/worker/tests/test_secret_key.py
@@ -0,0 +1,40 @@
+import base64
+
+import pytest
+
+from lyra_worker.crypto import PLACEHOLDER_SECRET_KEY, secret_key_problem
+
+_GOOD = base64.b64encode(b"x" * 32).decode()
+_LEGACY = "MDEyMzQ1Njc4OWFiY2RlZjAxMjM0NTY3ODlhYmNkZWY="
+
+
+@pytest.fixture(autouse=True)
+def _clean_env(monkeypatch):
+    monkeypatch.delenv("LYRA_SECRET_KEY", raising=False)
+
+
+def test_missing_key_is_fatal(monkeypatch):
+    assert secret_key_problem() == ("LYRA_SECRET_KEY is not set", True)
+
+
+def test_placeholder_is_fatal(monkeypatch):
+    monkeypatch.setenv("LYRA_SECRET_KEY", PLACEHOLDER_SECRET_KEY)
+    msg, fatal = secret_key_problem()
+    assert fatal is True and "placeholder" in msg
+
+
+def test_wrong_length_is_fatal(monkeypatch):
+    monkeypatch.setenv("LYRA_SECRET_KEY", base64.b64encode(b"short").decode())
+    msg, fatal = secret_key_problem()
+    assert fatal is True and "32 bytes" in msg
+
+
+def test_legacy_public_key_warns_not_fatal(monkeypatch):
+    monkeypatch.setenv("LYRA_SECRET_KEY", _LEGACY)
+    msg, fatal = secret_key_problem()
+    assert fatal is False and "PUBLIC" in msg
+
+
+def test_good_key_is_fine(monkeypatch):
+    monkeypatch.setenv("LYRA_SECRET_KEY", _GOOD)
+    assert secret_key_problem() is None