diff --git a/alembic/versions/0003_roles_settings.py b/alembic/versions/0003_roles_settings.py
new file mode 100644
index 0000000..50a2d12
--- /dev/null
+++ b/alembic/versions/0003_roles_settings.py
@@ -0,0 +1,32 @@
+"""roles + settings
+
+Revision ID: 0003
+Revises: 0002
+Create Date: 2026-07-19
+
+Adds the admin role bit and the DB-backed settings table. No rows are seeded —
+defaults live in the code registry (thoughtsync.settings), so an empty table
+means every setting is at its default.
+"""
+from alembic import op
+import sqlalchemy as sa
+
+revision = "0003"
+down_revision = "0002"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column("users", sa.Column("is_admin", sa.Boolean(), nullable=False, server_default=sa.false()))
+    op.create_table(
+        "settings",
+        sa.Column("key", sa.Text(), primary_key=True),
+        sa.Column("value", sa.Text(), nullable=False),
+        sa.Column("updated_at", sa.DateTime(timezone=True), nullable=False, server_default=sa.func.now()),
+    )
+
+
+def downgrade() -> None:
+    op.drop_table("settings")
+    op.drop_column("users", "is_admin")
diff --git a/src/thoughtsync/app.py b/src/thoughtsync/app.py
index 0c8551d..4a145de 100644
--- a/src/thoughtsync/app.py
+++ b/src/thoughtsync/app.py
@@ -1,34 +1,61 @@
 from __future__ import annotations
 
 import os
+import secrets
+from datetime import timedelta
 
 from quart import Quart, jsonify, send_from_directory
 
 from . import __version__
 from .auth import bp as auth_bp
 from .config import Config
+from .db import session_scope
 from .notes import bp as notes_bp
+from .settings import get_public_config, get_setting, load_or_create_secret_key
+from .settings_api import bp as settings_bp
 
 STATIC_DIR = os.path.join(os.path.dirname(__file__), "static")
 
 
 def create_app() -> Quart:
-    # static_folder=None: the SPA catch-all below owns static serving instead of
-    # Quart's default /static handler.
+    # static_folder=None: the SPA catch-all below owns static serving.
     app = Quart(__name__, static_folder=None)
-    app.secret_key = Config.secret_key()
+    # Ephemeral/env secret so the app (and DB-free unit tests) construct without a
+    # database. before_serving swaps in the real, DB-persisted key before serving.
+    app.secret_key = Config.secret_key_env() or secrets.token_urlsafe(48)
     app.config["APP_VERSION"] = os.environ.get("APP_VERSION", __version__)
+    app.config["SESSION_COOKIE_HTTPONLY"] = True
+    app.config["SESSION_COOKIE_SAMESITE"] = "Lax"
+    app.config["PERMANENT_SESSION_LIFETIME"] = timedelta(days=30)
 
     app.register_blueprint(auth_bp)
     app.register_blueprint(notes_bp)
+    app.register_blueprint(settings_bp)
+
+    @app.before_serving
+    async def _bootstrap() -> None:
+        # Load (or generate + persist) the real signing secret and the live session
+        # lifetime from the DB, before any request is served.
+        async with session_scope() as db:
+            app.secret_key = await load_or_create_secret_key(db)
+            try:
+                days = int(await get_setting(db, "session_ttl_days"))
+                app.config["PERMANENT_SESSION_LIFETIME"] = timedelta(days=days)
+            except (ValueError, TypeError, KeyError):
+                pass
 
     @app.get("/api/health")
     async def health():
         return jsonify({"status": "ok", "version": app.config["APP_VERSION"]})
 
-    # Serve the built Vue SPA (baked into static/ by the Docker build) with a
-    # history-fallback to index.html. In dev the Vite server proxies /api here, so
-    # a missing static/ dir is expected and simply 404s the frontend.
+    @app.get("/api/config")
+    async def public_config():
+        # Public: the login/register screen reads site name + whether signups are open.
+        async with session_scope() as db:
+            data = await get_public_config(db)
+        data["version"] = app.config["APP_VERSION"]
+        return jsonify(data)
+
     @app.get("/", defaults={"path": ""})
     @app.get("/<path:path>")
     async def spa(path: str):
diff --git a/src/thoughtsync/auth.py b/src/thoughtsync/auth.py
index 4a7f188..9114a71 100644
--- a/src/thoughtsync/auth.py
+++ b/src/thoughtsync/auth.py
@@ -4,11 +4,12 @@ import functools
 import uuid
 
 from quart import Blueprint, g, jsonify, request, session
-from sqlalchemy import select
+from sqlalchemy import func, select
 
 from .db import session_scope
 from .models.user import User
 from .security import hash_password, verify_password
+from .settings import get_setting
 
 bp = Blueprint("auth", __name__, url_prefix="/api/auth")
 
@@ -22,22 +23,52 @@ def _serialize_user(user: User) -> dict:
         "email": user.email,
         "display_name": user.display_name,
         "email_verified": user.email_verified,
+        "is_admin": user.is_admin,
     }
 
 
+def _session_user_id() -> uuid.UUID | None:
+    raw = session.get(SESSION_KEY)
+    if not raw:
+        return None
+    try:
+        return uuid.UUID(raw)
+    except (ValueError, TypeError):
+        session.pop(SESSION_KEY, None)
+        return None
+
+
 def login_required(fn):
     """Guard: 401 unless a valid session is present. Sets g.user_id for the view."""
 
     @functools.wraps(fn)
     async def wrapper(*args, **kwargs):
-        raw = session.get(SESSION_KEY)
-        if not raw:
+        uid = _session_user_id()
+        if uid is None:
             return jsonify({"error": "authentication required"}), 401
-        try:
-            g.user_id = uuid.UUID(raw)
-        except (ValueError, TypeError):
-            session.pop(SESSION_KEY, None)
+        g.user_id = uid
+        return await fn(*args, **kwargs)
+
+    return wrapper
+
+
+def require_admin(fn):
+    """Guard: 401 unauthenticated, 403 non-admin. Checks is_admin live from the DB
+    so a demoted admin loses access immediately."""
+
+    @functools.wraps(fn)
+    async def wrapper(*args, **kwargs):
+        uid = _session_user_id()
+        if uid is None:
             return jsonify({"error": "authentication required"}), 401
+        async with session_scope() as db:
+            user = await db.get(User, uid)
+            if user is None:
+                session.pop(SESSION_KEY, None)
+                return jsonify({"error": "authentication required"}), 401
+            if not user.is_admin:
+                return jsonify({"error": "admin access required"}), 403
+        g.user_id = uid
         return await fn(*args, **kwargs)
 
     return wrapper
@@ -58,14 +89,26 @@ async def register():
         display_name = email.split("@", 1)[0]
 
     async with session_scope() as db:
+        user_count = await db.scalar(select(func.count()).select_from(User)) or 0
+        is_first = user_count == 0
+        # The first account bootstraps the admin and is always allowed, even when
+        # registration is otherwise closed.
+        if not is_first and not await get_setting(db, "allow_registration"):
+            return jsonify({"error": "registration is closed"}), 403
         existing = await db.scalar(select(User).where(User.email == email))
         if existing is not None:
             return jsonify({"error": "an account with that email already exists"}), 409
-        user = User(email=email, password_hash=hash_password(password), display_name=display_name)
+        user = User(
+            email=email,
+            password_hash=hash_password(password),
+            display_name=display_name,
+            is_admin=is_first,
+        )
         db.add(user)
         await db.commit()
         await db.refresh(user)
         session[SESSION_KEY] = str(user.id)
+        session.permanent = True
         return jsonify(_serialize_user(user)), 201
 
 
@@ -80,6 +123,7 @@ async def login():
         if user is None or not user.password_hash or not verify_password(password, user.password_hash):
             return jsonify({"error": "invalid email or password"}), 401
         session[SESSION_KEY] = str(user.id)
+        session.permanent = True
         return jsonify(_serialize_user(user))
 
 
diff --git a/src/thoughtsync/config.py b/src/thoughtsync/config.py
index a9f3cf8..1e5f9b8 100644
--- a/src/thoughtsync/config.py
+++ b/src/thoughtsync/config.py
@@ -1,52 +1,37 @@
 from __future__ import annotations
 
 import os
-import secrets
 from pathlib import Path
 
 
 class Config:
-    """Runtime configuration.
+    """Bootstrap configuration.
 
-    Values come from environment variables with working local-dev defaults, so the
-    app boots with zero configuration (family rule 26 — integrations default to
-    working, never coerce setup). As the product grows, anything an operator wants
-    to tune moves into a DB-backed Settings UI (rule 25); env is bootstrap only.
+    For a basic install, ``THOUGHTSYNC_DATABASE_URL`` is the ONLY required env var —
+    every other tunable lives in the DB-backed Settings UI (rule 25). The remaining
+    env vars are optional "break-glass" / bootstrap items:
+
+    - ``THOUGHTSYNC_SECRET_KEY`` — optional override for the cookie-signing secret.
+      If unset, a key is generated and persisted in the DB (see
+      ``thoughtsync.settings.load_or_create_secret_key``), so sessions survive
+      restarts with no volume required.
+    - ``THOUGHTSYNC_DATA_DIR`` — optional, defaults to ``/var/thoughtsync``. Only
+      used for uploaded media (M2); irrelevant to a basic text-notes install.
     """
 
-    # Where runtime-generated secrets + uploaded media live.
     DATA_DIR = os.environ.get("THOUGHTSYNC_DATA_DIR", "/var/thoughtsync")
-    # Empty -> defaults to <DATA_DIR>/media (see media_root()).
     MEDIA_ROOT = os.environ.get("THOUGHTSYNC_MEDIA_ROOT", "")
 
-    # postgresql+asyncpg URL. Mirrors alembic.ini's local-dev default.
     DATABASE_URL = os.environ.get(
         "THOUGHTSYNC_DATABASE_URL",
         "postgresql+asyncpg://thoughtsync:thoughtsync@localhost:5432/thoughtsync",
     )
 
-    # Auth session cookie: a capture app should rarely log you out, so keep it long.
-    AUTH_TTL_SECONDS = 60 * 60 * 24 * 30  # 30 days
-
     @classmethod
     def media_root(cls) -> Path:
         return Path(cls.MEDIA_ROOT or os.path.join(cls.DATA_DIR, "media"))
 
     @classmethod
-    def secret_key(cls) -> bytes:
-        """Secret used to sign the auth session cookie.
-
-        Read from env if set; otherwise read/generate a persistent key file under
-        DATA_DIR so signed sessions survive restarts (no forced re-login on deploy).
-        """
-        env = os.environ.get("THOUGHTSYNC_SECRET_KEY")
-        if env:
-            return env.encode()
-        data_dir = Path(cls.DATA_DIR)
-        data_dir.mkdir(parents=True, exist_ok=True)
-        key_file = data_dir / "secret_key"
-        if key_file.exists():
-            return key_file.read_bytes()
-        key = secrets.token_bytes(32)
-        key_file.write_bytes(key)
-        return key
+    def secret_key_env(cls) -> str | None:
+        """Optional break-glass override for the cookie-signing secret."""
+        return os.environ.get("THOUGHTSYNC_SECRET_KEY") or None
diff --git a/src/thoughtsync/models/all.py b/src/thoughtsync/models/all.py
index 0e60076..d2136b5 100644
--- a/src/thoughtsync/models/all.py
+++ b/src/thoughtsync/models/all.py
@@ -3,4 +3,4 @@
 Imported for side effects only (model registration on Base.metadata).
 """
 
-from . import group, note, share, user  # noqa: F401
+from . import group, note, settings, share, user  # noqa: F401
diff --git a/src/thoughtsync/models/settings.py b/src/thoughtsync/models/settings.py
new file mode 100644
index 0000000..7525a90
--- /dev/null
+++ b/src/thoughtsync/models/settings.py
@@ -0,0 +1,22 @@
+from __future__ import annotations
+
+from datetime import datetime
+
+from sqlalchemy import DateTime, Text, func
+from sqlalchemy.orm import Mapped, mapped_column
+
+from . import Base
+
+
+class Setting(Base):
+    """A single persisted key/value setting. Values are JSON-encoded text; the
+    typed defaults + metadata live in the code registry (thoughtsync.settings), so
+    an empty table means "all defaults" (rule 26)."""
+
+    __tablename__ = "settings"
+
+    key: Mapped[str] = mapped_column(Text(), primary_key=True)
+    value: Mapped[str] = mapped_column(Text(), nullable=False)
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), nullable=False, server_default=func.now(), onupdate=func.now()
+    )
diff --git a/src/thoughtsync/models/user.py b/src/thoughtsync/models/user.py
index a6fe3ad..aad2fc9 100644
--- a/src/thoughtsync/models/user.py
+++ b/src/thoughtsync/models/user.py
@@ -17,6 +17,8 @@ class User(Base):
     # CITEXT so lookups/uniqueness are case-insensitive without lower() everywhere.
     email: Mapped[str] = mapped_column(CITEXT(), nullable=False, unique=True)
     email_verified: Mapped[bool] = mapped_column(Boolean(), nullable=False, server_default=func.false())
+    # First registered user becomes admin (see auth.register); admin gates Settings.
+    is_admin: Mapped[bool] = mapped_column(Boolean(), nullable=False, server_default=func.false())
     # Nullable: leaves room for external-identity-only accounts later (rule 26).
     password_hash: Mapped[str | None] = mapped_column(Text(), nullable=True)
     display_name: Mapped[str] = mapped_column(Text(), nullable=False)
diff --git a/src/thoughtsync/settings.py b/src/thoughtsync/settings.py
new file mode 100644
index 0000000..053932c
--- /dev/null
+++ b/src/thoughtsync/settings.py
@@ -0,0 +1,167 @@
+from __future__ import annotations
+
+import json
+import secrets
+from dataclasses import dataclass
+from datetime import datetime, timezone
+from typing import Any, Literal
+
+from .models.settings import Setting
+
+SettingType = Literal["string", "bool", "int"]
+
+
+@dataclass(frozen=True)
+class SettingDef:
+    key: str
+    type: SettingType
+    default: Any
+    label: str
+    description: str
+    group: str
+
+
+# The source of truth for every user-facing setting. Add a row here and it appears
+# in the admin Settings UI with a working default — no migration, no env var.
+REGISTRY: list[SettingDef] = [
+    SettingDef(
+        "site_name", "string", "ThoughtSync", "Site name", "Shown in the header and the browser tab.", "General"
+    ),
+    SettingDef(
+        "allow_registration",
+        "bool",
+        True,
+        "Allow new registrations",
+        "When off, only existing users can sign in. The first account is always allowed.",
+        "Access",
+    ),
+    SettingDef(
+        "session_ttl_days",
+        "int",
+        30,
+        "Session length (days)",
+        "How long a signed-in session stays valid before another login is required.",
+        "Access",
+    ),
+]
+
+_BY_KEY: dict[str, SettingDef] = {d.key: d for d in REGISTRY}
+
+# Internal, non-UI reserved key: the persisted cookie-signing secret. Stored in the
+# same table but never listed in the registry, so it never shows in the Settings UI.
+SECRET_KEY_SETTING = "secret_key"
+
+
+def _coerce_bool(raw: Any) -> bool:
+    if isinstance(raw, bool):
+        return raw
+    if isinstance(raw, str):
+        return raw.strip().lower() in ("1", "true", "yes", "on")
+    return bool(raw)
+
+
+def _coerce(defn: SettingDef, raw: Any) -> Any:
+    if defn.type == "bool":
+        return _coerce_bool(raw)
+    if defn.type == "int":
+        try:
+            return int(raw)
+        except (ValueError, TypeError):
+            return defn.default
+    return str(raw)
+
+
+async def _load_raw(db, key: str) -> Any:
+    row = await db.get(Setting, key)
+    if row is None:
+        return None
+    try:
+        return json.loads(row.value)
+    except (ValueError, TypeError):
+        return None
+
+
+async def _upsert(db, key: str, value: Any) -> None:
+    row = await db.get(Setting, key)
+    payload = json.dumps(value)
+    if row is None:
+        db.add(Setting(key=key, value=payload))
+    else:
+        row.value = payload
+        row.updated_at = datetime.now(timezone.utc)
+
+
+async def get_setting(db, key: str) -> Any:
+    defn = _BY_KEY.get(key)
+    if defn is None:
+        raise KeyError(key)
+    raw = await _load_raw(db, key)
+    return defn.default if raw is None else _coerce(defn, raw)
+
+
+async def get_public_config(db) -> dict:
+    """Non-sensitive settings the unauthenticated login/register screen needs."""
+    return {
+        "site_name": await get_setting(db, "site_name"),
+        "allow_registration": await get_setting(db, "allow_registration"),
+    }
+
+
+async def get_admin_settings(db) -> list[dict]:
+    """Every registry setting with its current value + metadata, for the admin UI."""
+    result: list[dict] = []
+    for d in REGISTRY:
+        result.append(
+            {
+                "key": d.key,
+                "type": d.type,
+                "value": await get_setting(db, d.key),
+                "default": d.default,
+                "label": d.label,
+                "description": d.description,
+                "group": d.group,
+            }
+        )
+    return result
+
+
+def validate_updates(updates: dict) -> tuple[dict, str | None]:
+    """Coerce/validate a {key: value} dict against the registry. Returns
+    (clean_values, error_message). An unknown key or a bad int is rejected."""
+    clean: dict = {}
+    for key, val in updates.items():
+        defn = _BY_KEY.get(key)
+        if defn is None:
+            return {}, f"unknown setting: {key}"
+        if defn.type == "int":
+            try:
+                clean[key] = int(val)
+            except (ValueError, TypeError):
+                return {}, f"{defn.label} must be a whole number"
+        elif defn.type == "bool":
+            clean[key] = _coerce_bool(val)
+        else:
+            clean[key] = str(val)
+    return clean, None
+
+
+async def set_settings(db, updates: dict) -> None:
+    for key, value in updates.items():
+        await _upsert(db, key, value)
+
+
+async def load_or_create_secret_key(db) -> str:
+    """Return the persisted cookie-signing secret, generating + storing one on first
+    run. Keeps sessions valid across restarts with no env var or volume required."""
+    row = await db.get(Setting, SECRET_KEY_SETTING)
+    if row is not None:
+        try:
+            val = json.loads(row.value)
+            if isinstance(val, str) and val:
+                return val
+        except (ValueError, TypeError):
+            pass
+    key = secrets.token_urlsafe(48)
+    await _upsert(db, SECRET_KEY_SETTING, key)
+    await db.commit()
+    return key
diff --git a/src/thoughtsync/settings_api.py b/src/thoughtsync/settings_api.py
new file mode 100644
index 0000000..4efeca1
--- /dev/null
+++ b/src/thoughtsync/settings_api.py
@@ -0,0 +1,44 @@
+from __future__ import annotations
+
+from datetime import timedelta
+
+from quart import Blueprint, current_app, jsonify, request
+
+from .auth import require_admin
+from .db import session_scope
+from .settings import get_admin_settings, set_settings, validate_updates
+
+bp = Blueprint("settings", __name__, url_prefix="/api/settings")
+
+
+@bp.get("")
+@require_admin
+async def list_settings():
+    async with session_scope() as db:
+        return jsonify({"settings": await get_admin_settings(db)})
+
+
+@bp.patch("")
+@require_admin
+async def update_settings():
+    raw = await request.get_json(silent=True)
+    data = raw if isinstance(raw, dict) else {}
+    # Accept either {settings: {...}} or a bare {key: value} object.
+    updates = data.get("settings") if isinstance(data.get("settings"), dict) else data
+    if not isinstance(updates, dict):
+        return jsonify({"error": "expected an object of settings"}), 400
+
+    clean, error = validate_updates(updates)
+    if error is not None:
+        return jsonify({"error": error}), 400
+
+    async with session_scope() as db:
+        await set_settings(db, clean)
+        await db.commit()
+        result = await get_admin_settings(db)
+
+    # Apply the live-tunable knob without a restart (rule 25).
+    if "session_ttl_days" in clean:
+        current_app.config["PERMANENT_SESSION_LIFETIME"] = timedelta(days=int(clean["session_ttl_days"]))
+
+    return jsonify({"settings": result})
diff --git a/tests/test_admin.py b/tests/test_admin.py
new file mode 100644
index 0000000..09109dd
--- /dev/null
+++ b/tests/test_admin.py
@@ -0,0 +1,21 @@
+import pytest
+
+from thoughtsync.app import create_app
+
+
+@pytest.fixture
+def app():
+    return create_app()
+
+
+async def test_settings_requires_auth(app):
+    # require_admin returns 401 before any DB access when unauthenticated.
+    client = app.test_client()
+    resp = await client.get("/api/settings")
+    assert resp.status_code == 401
+
+
+async def test_settings_patch_requires_auth(app):
+    client = app.test_client()
+    resp = await client.patch("/api/settings", json={"site_name": "x"})
+    assert resp.status_code == 401
diff --git a/tests/test_settings.py b/tests/test_settings.py
new file mode 100644
index 0000000..4dd9b8c
--- /dev/null
+++ b/tests/test_settings.py
@@ -0,0 +1,25 @@
+from thoughtsync.settings import REGISTRY, validate_updates
+
+
+def test_registry_has_expected_keys():
+    keys = {d.key for d in REGISTRY}
+    assert {"site_name", "allow_registration", "session_ttl_days"} <= keys
+
+
+def test_validate_rejects_unknown_key():
+    clean, error = validate_updates({"nope": 1})
+    assert error is not None
+    assert clean == {}
+
+
+def test_validate_coerces_bool_and_int():
+    clean, error = validate_updates({"allow_registration": "true", "session_ttl_days": "45"})
+    assert error is None
+    assert clean["allow_registration"] is True
+    assert clean["session_ttl_days"] == 45
+
+
+def test_validate_rejects_bad_int():
+    clean, error = validate_updates({"session_ttl_days": "not-a-number"})
+    assert error is not None
+    assert clean == {}