diff --git a/backend/.env.example b/backend/.env.example
index 67ca3ce..d7f5062 100644
--- a/backend/.env.example
+++ b/backend/.env.example
@@ -52,7 +52,18 @@ GCS_BUCKET=
 # Frontend URL(s), JSON list
 CORS_ORIGINS=["http://localhost:3000","http://127.0.0.1:3000","http://localhost:18742","http://127.0.0.1:18742"]
 
-# -- DigiKey (optional) ------------------------------------------------------
+# -- Auth (self-host) --------------------------------------------------------
+# Set AUTH_JWT_SECRET to enable Pinscope email/password accounts and
+# multi-user project collaborators (invite by email). Clerk keys, if set,
+# take priority over local auth.
+# AUTH_JWT_SECRET=change-me-to-a-long-random-string
+# Comma-separated emails that are admin on register (first user is always admin)
+# AUTH_ADMIN_EMAILS=you@example.com
+
+# -- Clerk (optional cloud auth) ---------------------------------------------
+# CLERK_SECRET_KEY=
+# CLERK_PUBLISHABLE_KEY=
+# CLERK_JWKS_URL=
 # Optional catalog datasheet source and parameter-based passive auto-resolve.
 # Order: BOM URL → LCSC → manufacturer PDF URLs → Mouser → DigiKey.
 # DIGIKEY_CLIENT_ID=
diff --git a/backend/config.py b/backend/config.py
index e2a6cd9..c35c125 100644
--- a/backend/config.py
+++ b/backend/config.py
@@ -119,11 +119,18 @@ class Settings(BaseSettings):
     # GCS (if set, use GCSStorageBackend; otherwise LocalStorageBackend)
     gcs_bucket: str = ""
 
-    # Clerk authentication
+    # Clerk authentication (cloud). When set, takes priority over local auth.
     clerk_secret_key: str = ""
     clerk_publishable_key: str = ""
     clerk_jwks_url: str = ""
 
+    # Local Pinscope auth (self-host). Set AUTH_JWT_SECRET to enable email/password
+    # accounts and multi-user project collaborators without Clerk.
+    auth_jwt_secret: str = ""
+    # Comma-separated emails that become admin on register (in addition to the
+    # first account, which is always admin).
+    auth_admin_emails: str = ""
+
     # DigiKey API (optional — enables auto-fetch datasheets)
     digikey_client_id: str = ""
     digikey_client_secret: str = ""
@@ -212,9 +219,18 @@ class Settings(BaseSettings):
         return bool(self.gcs_bucket)
 
     @property
-    def use_auth(self) -> bool:
+    def use_clerk(self) -> bool:
         return bool(self.clerk_secret_key and self.clerk_jwks_url)
 
+    @property
+    def use_local_auth(self) -> bool:
+        """Self-host email/password auth when JWT secret is set and Clerk is not."""
+        return bool(self.auth_jwt_secret) and not self.use_clerk
+
+    @property
+    def use_auth(self) -> bool:
+        return self.use_clerk or self.use_local_auth
+
     @property
     def use_email(self) -> bool:
         return bool(self.email_sender and self.email_frontend_url)
diff --git a/backend/main.py b/backend/main.py
index 47d4481..2c604cd 100644
--- a/backend/main.py
+++ b/backend/main.py
@@ -10,7 +10,7 @@ from fastapi.responses import JSONResponse
 from starlette.middleware.base import BaseHTTPMiddleware
 
 from backend.config import settings
-from backend.routers import admin, contact, feedback, impedance, pipeline, projects, reports, survey
+from backend.routers import admin, auth, contact, feedback, impedance, pipeline, projects, reports, survey
 from backend.services.projects import ProjectNotFound
 from backend.services.storage import LocalStorageBackend
 
@@ -35,14 +35,18 @@ async def lifespan(app: FastAPI):
     env = os.getenv("ENVIRONMENT", "").lower()
     if env == "production" and not settings.use_auth:
         raise RuntimeError(
-            "CLERK_JWKS_URL and CLERK_SECRET_KEY must be set in production. "
-            "Authentication cannot be disabled in production."
+            "Production requires authentication: set AUTH_JWT_SECRET "
+            "(local Pinscope accounts) or CLERK_JWKS_URL + CLERK_SECRET_KEY."
         )
     if not settings.use_auth:
         logger.warning(
             "Authentication is DISABLED — all users have full access. "
             "This is only safe for local development."
         )
+    elif settings.use_local_auth:
+        logger.info("Local Pinscope authentication enabled (AUTH_JWT_SECRET)")
+    elif settings.use_clerk:
+        logger.info("Clerk authentication enabled")
     if not settings.billing_enabled:
         logger.warning(
             "Billing is DISABLED — pipelines run free and the billing/credits "
@@ -55,6 +59,8 @@ async def lifespan(app: FastAPI):
     if isinstance(app.state.storage, LocalStorageBackend):
         base = settings.data_dir
         (base / "users").mkdir(parents=True, exist_ok=True)
+        (base / "auth" / "users").mkdir(parents=True, exist_ok=True)
+        (base / "auth" / "by_email").mkdir(parents=True, exist_ok=True)
         (base / "library" / "extracted").mkdir(parents=True, exist_ok=True)
         (base / "library" / "patterns").mkdir(parents=True, exist_ok=True)
         (base / "library" / "models").mkdir(parents=True, exist_ok=True)
@@ -84,31 +90,37 @@ class SecurityHeadersMiddleware(BaseHTTPMiddleware):
 
 
 class AuthMiddleware(BaseHTTPMiddleware):
-    """Extract user_id from Clerk JWT or default to local dev user."""
+    """Extract user_id from JWT (Clerk or local) or default to local dev user."""
 
     async def dispatch(self, request: Request, call_next):
         # Let CORS preflight through — browsers send OPTIONS without credentials
         if request.method == "OPTIONS":
             return await call_next(request)
         # Public endpoints that don't require authentication
-        if request.url.path == "/api/contact":
+        if request.url.path in {
+            "/api/contact",
+            "/api/auth/mode",
+            "/api/auth/register",
+            "/api/auth/login",
+        }:
             request.state.user_id = LOCAL_DEV_USER
             return await call_next(request)
         if settings.use_auth:
-            from backend.middleware.auth import verify_clerk_token
+            from backend.middleware.auth import verify_request_user
 
-            user_id = await verify_clerk_token(request)
+            user_id = await verify_request_user(request)
             if user_id is None:
                 is_production = os.getenv("ENVIRONMENT", "").lower() == "production"
-                if is_production:
+                # Local auth (and production) require a valid token for API routes.
+                if is_production or settings.use_local_auth:
                     from fastapi.responses import JSONResponse
 
                     return JSONResponse(
                         status_code=401,
                         content={"detail": "Authentication required"},
                     )
-                # Non-production: fall back to local dev user so Clerk config
-                # doesn't block local development when no token is present.
+                # Non-production Clerk: fall back so missing token doesn't block
+                # local development when Clerk is configured but unused.
                 user_id = LOCAL_DEV_USER
             request.state.user_id = user_id
         else:
@@ -149,6 +161,7 @@ app.include_router(pipeline.router, prefix="/api")
 app.include_router(reports.router, prefix="/api")
 app.include_router(impedance.router, prefix="/api")
 app.include_router(admin.router, prefix="/api")
+app.include_router(auth.router, prefix="/api")
 if settings.billing_enabled:
     # Import guarded too: with billing disabled the core never loads the
     # billing/credits routers (or, transitively, the Stripe SDK).
diff --git a/backend/middleware/auth.py b/backend/middleware/auth.py
index 0a15b8a..cdd1530 100644
--- a/backend/middleware/auth.py
+++ b/backend/middleware/auth.py
@@ -1,12 +1,7 @@
-"""Clerk JWT verification for FastAPI.
-
-Validates JWT tokens from the Authorization header against Clerk's JWKS endpoint.
-Extracts user_id (sub claim) for per-user storage scoping.
-"""
+"""JWT verification for FastAPI (Clerk JWKS or local Pinscope HS256)."""
 
 from __future__ import annotations
 
-import time
 from typing import Any
 
 import jwt
@@ -16,7 +11,17 @@ from backend.config import settings
 
 # JWKS cache
 _jwks_client: jwt.PyJWKClient | None = None
-_SKIP_PATHS = {"/docs", "/openapi.json", "/redoc", "/health", "/api/billing/webhook"}
+_SKIP_PATHS = {
+    "/docs",
+    "/openapi.json",
+    "/redoc",
+    "/health",
+    "/api/billing/webhook",
+    "/api/auth/mode",
+    "/api/auth/register",
+    "/api/auth/login",
+    "/api/contact",
+}
 
 
 def _get_jwks_client() -> jwt.PyJWKClient:
@@ -24,38 +29,30 @@ def _get_jwks_client() -> jwt.PyJWKClient:
     if _jwks_client is None:
         jwks_url = settings.clerk_jwks_url
         if not jwks_url:
-            # Default Clerk JWKS URL derived from publishable key
-            # Clerk publishable keys start with pk_test_ or pk_live_
-            # JWKS is at https://{clerk-frontend-api}/.well-known/jwks.json
-            # The user must set CLERK_JWKS_URL explicitly
             raise RuntimeError(
-                "CLERK_JWKS_URL must be set for authentication. "
+                "CLERK_JWKS_URL must be set for Clerk authentication. "
                 "Find it in your Clerk dashboard under API Keys."
             )
         _jwks_client = jwt.PyJWKClient(jwks_url, cache_keys=True)
     return _jwks_client
 
 
-async def verify_clerk_token(request: Request) -> str | None:
-    """Verify Clerk JWT and return user_id, or None if invalid.
+def _bearer_or_query_token(request: Request) -> str | None:
+    auth_header = request.headers.get("authorization", "")
+    if auth_header.startswith("Bearer "):
+        return auth_header[7:]
+    # EventSource/SSE can't send headers
+    return request.query_params.get("token")
 
-    Returns None for:
-    - Missing Authorization header
-    - Invalid/expired token
-    - Skip paths (docs, health)
-    """
-    # Skip auth for docs/health endpoints
+
+async def verify_clerk_token(request: Request) -> str | None:
+    """Verify Clerk JWT and return user_id, or None if invalid."""
     if request.url.path in _SKIP_PATHS:
         return "anonymous"
 
-    auth_header = request.headers.get("authorization", "")
-    if not auth_header.startswith("Bearer "):
-        # Fallback: check query param (EventSource/SSE can't send headers)
-        token = request.query_params.get("token")
-        if not token:
-            return None
-    else:
-        token = auth_header[7:]
+    token = _bearer_or_query_token(request)
+    if not token:
+        return None
 
     try:
         client = _get_jwks_client()
@@ -67,19 +64,20 @@ async def verify_clerk_token(request: Request) -> str | None:
             algorithms=["RS256"],
             options={
                 "verify_exp": True,
-                "verify_aud": False,  # Clerk doesn't always set aud
+                "verify_aud": False,
                 "verify_iss": True,
             },
-            # Clerk tokens use the Clerk instance URL as issuer
-            # e.g. https://abc123.clerk.accounts.dev from https://abc123.clerk.accounts.dev/.well-known/jwks.json
-            issuer=settings.clerk_jwks_url.replace("/.well-known/jwks.json", "") if settings.clerk_jwks_url else None,
-            leeway=10,  # 10 second clock skew tolerance
+            issuer=(
+                settings.clerk_jwks_url.replace("/.well-known/jwks.json", "")
+                if settings.clerk_jwks_url
+                else None
+            ),
+            leeway=10,
         )
 
         user_id = payload.get("sub")
         if not user_id:
             return None
-
         return user_id
 
     except jwt.ExpiredSignatureError:
@@ -88,3 +86,30 @@ async def verify_clerk_token(request: Request) -> str | None:
         return None
     except Exception:
         return None
+
+
+async def verify_local_token(request: Request) -> str | None:
+    """Verify Pinscope local JWT and return user_id, or None if invalid."""
+    if request.url.path in _SKIP_PATHS:
+        return "anonymous"
+
+    token = _bearer_or_query_token(request)
+    if not token:
+        return None
+
+    from backend.services.local_jwt import decode_token
+
+    payload = decode_token(token)
+    if not payload:
+        return None
+    user_id = payload.get("sub")
+    return str(user_id) if user_id else None
+
+
+async def verify_request_user(request: Request) -> str | None:
+    """Dispatch to Clerk or local JWT verification."""
+    if settings.use_clerk:
+        return await verify_clerk_token(request)
+    if settings.use_local_auth:
+        return await verify_local_token(request)
+    return None
diff --git a/backend/routers/admin.py b/backend/routers/admin.py
index 1dc0e08..716b810 100644
--- a/backend/routers/admin.py
+++ b/backend/routers/admin.py
@@ -41,6 +41,14 @@ async def is_admin(request: Request) -> bool:
         request.state._is_admin = True
         return True
 
+    if settings.use_local_auth:
+        from backend.services import local_users
+
+        user = local_users.get_user(user_id)
+        result = bool(user and user.is_admin)
+        request.state._is_admin = result
+        return result
+
     # Fetch user from Clerk Backend API and check public_metadata.role
     try:
         async with httpx.AsyncClient() as client:
diff --git a/backend/routers/auth.py b/backend/routers/auth.py
new file mode 100644
index 0000000..9796033
--- /dev/null
+++ b/backend/routers/auth.py
@@ -0,0 +1,73 @@
+"""Local Pinscope auth endpoints (register / login / me)."""
+
+from __future__ import annotations
+
+from fastapi import APIRouter, HTTPException, Request
+from pydantic import BaseModel, Field
+
+from backend.config import settings
+from backend.services import local_jwt, local_users
+
+router = APIRouter(prefix="/auth", tags=["auth"])
+
+
+class RegisterRequest(BaseModel):
+    email: str
+    password: str = Field(min_length=8)
+    name: str | None = None
+
+
+class LoginRequest(BaseModel):
+    email: str
+    password: str
+
+
+def _require_local_auth() -> None:
+    if not settings.use_local_auth:
+        raise HTTPException(
+            400,
+            "Local auth is not enabled. Set AUTH_JWT_SECRET on the server.",
+        )
+
+
+@router.get("/mode")
+async def auth_mode():
+    """Public: how the frontend should authenticate."""
+    if settings.use_clerk:
+        return {"mode": "clerk", "auth_enabled": True}
+    if settings.use_local_auth:
+        return {"mode": "local", "auth_enabled": True}
+    return {"mode": "off", "auth_enabled": False}
+
+
+@router.post("/register")
+async def register(body: RegisterRequest):
+    _require_local_auth()
+    try:
+        user = local_users.create_user(body.email, body.password, body.name)
+    except ValueError as e:
+        raise HTTPException(400, str(e)) from e
+    token = local_jwt.issue_token(user.user_id, user.email)
+    return {"token": token, "user": user.public()}
+
+
+@router.post("/login")
+async def login(body: LoginRequest):
+    _require_local_auth()
+    user = local_users.authenticate(body.email, body.password)
+    if not user:
+        raise HTTPException(401, "Invalid email or password")
+    token = local_jwt.issue_token(user.user_id, user.email)
+    return {"token": token, "user": user.public()}
+
+
+@router.get("/me")
+async def me(request: Request):
+    _require_local_auth()
+    user_id = getattr(request.state, "user_id", None)
+    if not user_id or user_id == "local" or user_id == "anonymous":
+        raise HTTPException(401, "Authentication required")
+    user = local_users.get_user(user_id)
+    if not user:
+        raise HTTPException(401, "User not found")
+    return user.public()
diff --git a/backend/routers/projects.py b/backend/routers/projects.py
index dfa5afb..d4c1952 100644
--- a/backend/routers/projects.py
+++ b/backend/routers/projects.py
@@ -716,27 +716,17 @@ async def list_collaborators(project_id: str, request: Request):
     all_user_ids = [owner_user_id] + [c for c in meta.collaborators if c != owner_user_id]
     collaborators = []
     if settings.use_auth:
-        async with httpx.AsyncClient() as client:
-            for uid in all_user_ids:
-                entry: dict = {"user_id": uid, "name": None, "email": None, "image_url": None,
-                               "role": "owner" if uid == owner_user_id else "collaborator"}
-                try:
-                    resp = await client.get(
-                        f"https://api.clerk.com/v1/users/{uid}",
-                        headers={"Authorization": f"Bearer {settings.clerk_secret_key}"},
-                    )
-                    if resp.status_code == 200:
-                        clerk = resp.json()
-                        first = clerk.get("first_name") or ""
-                        last = clerk.get("last_name") or ""
-                        entry["name"] = f"{first} {last}".strip() or None
-                        emails = clerk.get("email_addresses", [])
-                        if emails:
-                            entry["email"] = emails[0].get("email_address")
-                        entry["image_url"] = clerk.get("image_url")
-                except Exception:
-                    pass
-                collaborators.append(entry)
+        from backend.services.user_directory import get_user_profile
+
+        for uid in all_user_ids:
+            profile = await get_user_profile(uid)
+            collaborators.append({
+                "user_id": uid,
+                "name": profile.get("name"),
+                "email": profile.get("email"),
+                "image_url": profile.get("image_url"),
+                "role": "owner" if uid == owner_user_id else "collaborator",
+            })
     else:
         # Local dev — just return user_ids without enrichment
         collaborators = [
@@ -762,22 +752,9 @@ async def add_collaborator(project_id: str, req: AddCollaboratorRequest, request
     if not settings.use_auth:
         raise HTTPException(400, "Collaboration requires authentication to be enabled")
 
-    # Look up user by email via Clerk Backend API
-    async with httpx.AsyncClient() as client:
-        resp = await client.get(
-            "https://api.clerk.com/v1/users",
-            params={"email_address": [req.email]},
-            headers={"Authorization": f"Bearer {settings.clerk_secret_key}"},
-        )
-    if resp.status_code != 200:
-        raise HTTPException(502, "Failed to look up user")
+    from backend.services.user_directory import find_user_id_by_email, get_user_profile
 
-    users = resp.json()
-    if not users:
-        raise HTTPException(404, "No user found with that email")
-
-    clerk_user = users[0]
-    collab_user_id = clerk_user.get("id")
+    collab_user_id = await find_user_id_by_email(req.email)
     if not collab_user_id:
         raise HTTPException(404, "No user found with that email")
 
@@ -791,15 +768,12 @@ async def add_collaborator(project_id: str, req: AddCollaboratorRequest, request
 
     proj_svc.add_collaborator(storage, user_id, project_id, collab_user_id)
 
-    # Return the collaborator info
-    first = clerk_user.get("first_name") or ""
-    last = clerk_user.get("last_name") or ""
-    emails = clerk_user.get("email_addresses", [])
+    profile = await get_user_profile(collab_user_id)
     return {
         "user_id": collab_user_id,
-        "name": f"{first} {last}".strip() or None,
-        "email": emails[0].get("email_address") if emails else None,
-        "image_url": clerk_user.get("image_url"),
+        "name": profile.get("name"),
+        "email": profile.get("email"),
+        "image_url": profile.get("image_url"),
     }
 
 
diff --git a/backend/services/local_jwt.py b/backend/services/local_jwt.py
new file mode 100644
index 0000000..90cf8f4
--- /dev/null
+++ b/backend/services/local_jwt.py
@@ -0,0 +1,45 @@
+"""Pinscope local JWT helpers (HS256)."""
+
+from __future__ import annotations
+
+from datetime import datetime, timedelta, timezone
+from typing import Any
+
+import jwt
+
+from backend.config import settings
+
+ALGORITHM = "HS256"
+TOKEN_TTL_DAYS = 30
+
+
+def issue_token(user_id: str, email: str) -> str:
+    secret = settings.auth_jwt_secret
+    if not secret:
+        raise RuntimeError("AUTH_JWT_SECRET is not configured")
+    now = datetime.now(timezone.utc)
+    payload = {
+        "sub": user_id,
+        "email": email,
+        "iss": "pinscope-local",
+        "iat": now,
+        "exp": now + timedelta(days=TOKEN_TTL_DAYS),
+    }
+    return jwt.encode(payload, secret, algorithm=ALGORITHM)
+
+
+def decode_token(token: str) -> dict[str, Any] | None:
+    secret = settings.auth_jwt_secret
+    if not secret:
+        return None
+    try:
+        return jwt.decode(
+            token,
+            secret,
+            algorithms=[ALGORITHM],
+            issuer="pinscope-local",
+            options={"verify_aud": False},
+            leeway=10,
+        )
+    except jwt.PyJWTError:
+        return None
diff --git a/backend/services/local_users.py b/backend/services/local_users.py
new file mode 100644
index 0000000..8380490
--- /dev/null
+++ b/backend/services/local_users.py
@@ -0,0 +1,204 @@
+"""Local Pinscope user directory (self-host auth, no Clerk).
+
+Users live under ``data/auth/users/{user_id}.json`` with an email index.
+Passwords use stdlib ``hashlib.scrypt``.
+"""
+
+from __future__ import annotations
+
+import hashlib
+import json
+import logging
+import re
+import secrets
+import shutil
+import uuid
+from dataclasses import asdict, dataclass
+from pathlib import Path
+
+from backend.config import settings
+
+logger = logging.getLogger(__name__)
+
+_EMAIL_RE = re.compile(r"^[^@\s]+@[^@\s]+\.[^@\s]+$")
+
+
+@dataclass
+class LocalUser:
+    user_id: str
+    email: str
+    name: str | None
+    password_hash: str
+    is_admin: bool = False
+    created_at: str = ""
+
+    def public(self) -> dict:
+        return {
+            "user_id": self.user_id,
+            "email": self.email,
+            "name": self.name,
+            "is_admin": self.is_admin,
+        }
+
+
+def _auth_root() -> Path:
+    root = Path(settings.data_dir) / "auth"
+    (root / "users").mkdir(parents=True, exist_ok=True)
+    (root / "by_email").mkdir(parents=True, exist_ok=True)
+    return root
+
+
+def _email_key(email: str) -> str:
+    return email.strip().lower()
+
+
+def _email_path(email: str) -> Path:
+    # Filesystem-safe key from normalized email
+    key = _email_key(email).replace("/", "_")
+    return _auth_root() / "by_email" / f"{key}.json"
+
+
+def _user_path(user_id: str) -> Path:
+    return _auth_root() / "users" / f"{user_id}.json"
+
+
+def hash_password(password: str, *, salt: bytes | None = None) -> str:
+    if salt is None:
+        salt = secrets.token_bytes(16)
+    digest = hashlib.scrypt(
+        password.encode("utf-8"), salt=salt, n=2**14, r=8, p=1, dklen=32
+    )
+    return f"scrypt${salt.hex()}${digest.hex()}"
+
+
+def verify_password(password: str, encoded: str) -> bool:
+    try:
+        algo, salt_hex, digest_hex = encoded.split("$", 2)
+    except ValueError:
+        return False
+    if algo != "scrypt":
+        return False
+    salt = bytes.fromhex(salt_hex)
+    check = hash_password(password, salt=salt)
+    return secrets.compare_digest(check, encoded)
+
+
+def validate_email(email: str) -> str:
+    e = email.strip().lower()
+    if not _EMAIL_RE.match(e):
+        raise ValueError("Invalid email address")
+    return e
+
+
+def validate_password(password: str) -> None:
+    if len(password) < 8:
+        raise ValueError("Password must be at least 8 characters")
+
+
+def get_user(user_id: str) -> LocalUser | None:
+    path = _user_path(user_id)
+    if not path.is_file():
+        return None
+    data = json.loads(path.read_text(encoding="utf-8"))
+    return LocalUser(**data)
+
+
+def find_by_email(email: str) -> LocalUser | None:
+    path = _email_path(email)
+    if not path.is_file():
+        return None
+    data = json.loads(path.read_text(encoding="utf-8"))
+    uid = data.get("user_id")
+    if not uid:
+        return None
+    return get_user(uid)
+
+
+def list_users() -> list[LocalUser]:
+    users_dir = _auth_root() / "users"
+    out: list[LocalUser] = []
+    for path in sorted(users_dir.glob("*.json")):
+        try:
+            out.append(LocalUser(**json.loads(path.read_text(encoding="utf-8"))))
+        except Exception:
+            logger.exception("Skipping corrupt user file %s", path)
+    return out
+
+
+def _save_user(user: LocalUser) -> None:
+    _user_path(user.user_id).write_text(
+        json.dumps(asdict(user), indent=2) + "\n", encoding="utf-8"
+    )
+    _email_path(user.email).write_text(
+        json.dumps({"user_id": user.user_id}) + "\n", encoding="utf-8"
+    )
+
+
+def user_count() -> int:
+    return len(list((_auth_root() / "users").glob("*.json")))
+
+
+def _migrate_local_projects(new_owner_id: str) -> int:
+    """Move ``users/local/projects/*`` under the first admin, if present."""
+    local_projects = Path(settings.data_dir) / "users" / "local" / "projects"
+    if not local_projects.is_dir():
+        return 0
+    dest_root = Path(settings.data_dir) / "users" / new_owner_id / "projects"
+    dest_root.mkdir(parents=True, exist_ok=True)
+    moved = 0
+    for child in local_projects.iterdir():
+        if not child.is_dir():
+            continue
+        target = dest_root / child.name
+        if target.exists():
+            continue
+        shutil.move(str(child), str(target))
+        moved += 1
+        logger.info("Migrated project %s → user %s", child.name, new_owner_id)
+    return moved
+
+
+def create_user(email: str, password: str, name: str | None = None) -> LocalUser:
+    email = validate_email(email)
+    validate_password(password)
+    if find_by_email(email):
+        raise ValueError("An account with that email already exists")
+
+    from datetime import datetime, timezone
+
+    first = user_count() == 0
+    admin_emails = {
+        e.strip().lower()
+        for e in (settings.auth_admin_emails or "").split(",")
+        if e.strip()
+    }
+    is_admin = first or email in admin_emails
+
+    user = LocalUser(
+        user_id="usr_" + uuid.uuid4().hex,
+        email=email,
+        name=(name or "").strip() or None,
+        password_hash=hash_password(password),
+        is_admin=is_admin,
+        created_at=datetime.now(timezone.utc).isoformat(),
+    )
+    _save_user(user)
+
+    if first:
+        try:
+            n = _migrate_local_projects(user.user_id)
+            if n:
+                logger.info("First admin inherited %s local project(s)", n)
+        except Exception:
+            logger.exception("Failed to migrate users/local projects")
+
+    return user
+
+
+def authenticate(email: str, password: str) -> LocalUser | None:
+    user = find_by_email(email)
+    if not user:
+        return None
+    if not verify_password(password, user.password_hash):
+        return None
+    return user
diff --git a/backend/services/user_directory.py b/backend/services/user_directory.py
new file mode 100644
index 0000000..fb1d5d6
--- /dev/null
+++ b/backend/services/user_directory.py
@@ -0,0 +1,81 @@
+"""User profile lookup for collaborators / admin — Clerk or local auth."""
+
+from __future__ import annotations
+
+import logging
+
+from backend.config import settings
+
+logger = logging.getLogger(__name__)
+
+
+async def find_user_id_by_email(email: str) -> str | None:
+    email = email.strip().lower()
+    if not email:
+        return None
+    if settings.use_clerk:
+        import httpx
+
+        async with httpx.AsyncClient() as client:
+            resp = await client.get(
+                "https://api.clerk.com/v1/users",
+                params={"email_address": [email]},
+                headers={"Authorization": f"Bearer {settings.clerk_secret_key}"},
+            )
+        if resp.status_code != 200:
+            logger.warning("Clerk email lookup failed: %s", resp.status_code)
+            return None
+        users = resp.json()
+        if not users:
+            return None
+        return users[0].get("id")
+    if settings.use_local_auth:
+        from backend.services import local_users
+
+        user = local_users.find_by_email(email)
+        return user.user_id if user else None
+    return None
+
+
+async def get_user_profile(user_id: str) -> dict:
+    """Return {user_id, name, email, image_url, is_admin?}."""
+    entry = {
+        "user_id": user_id,
+        "name": None,
+        "email": None,
+        "image_url": None,
+        "is_admin": False,
+    }
+    if settings.use_clerk:
+        import httpx
+
+        try:
+            async with httpx.AsyncClient() as client:
+                resp = await client.get(
+                    f"https://api.clerk.com/v1/users/{user_id}",
+                    headers={"Authorization": f"Bearer {settings.clerk_secret_key}"},
+                )
+            if resp.status_code == 200:
+                clerk = resp.json()
+                first = clerk.get("first_name") or ""
+                last = clerk.get("last_name") or ""
+                entry["name"] = f"{first} {last}".strip() or None
+                emails = clerk.get("email_addresses", [])
+                if emails:
+                    entry["email"] = emails[0].get("email_address")
+                entry["image_url"] = clerk.get("image_url")
+                role = (clerk.get("public_metadata") or {}).get("role")
+                entry["is_admin"] = role == "admin"
+        except Exception:
+            logger.exception("Clerk profile fetch failed for %s", user_id)
+        return entry
+    if settings.use_local_auth:
+        from backend.services import local_users
+
+        user = local_users.get_user(user_id)
+        if user:
+            entry["name"] = user.name
+            entry["email"] = user.email
+            entry["is_admin"] = user.is_admin
+        return entry
+    return entry
diff --git a/docker-compose.yml b/docker-compose.yml
index e1f43c3..21fade5 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -32,6 +32,7 @@ services:
       dockerfile: dockerfile
       args:
         NEXT_PUBLIC_API_URL: ${NEXT_PUBLIC_API_URL:-http://localhost:8080}
+        NEXT_PUBLIC_AUTH_MODE: ${NEXT_PUBLIC_AUTH_MODE:-}
 
     container_name: pinscope-frontend
     restart: unless-stopped
diff --git a/frontend/content/changelog.md b/frontend/content/changelog.md
index 83f5eb0..06fa377 100644
--- a/frontend/content/changelog.md
+++ b/frontend/content/changelog.md
@@ -2,6 +2,14 @@
 
 What's new in Pinscope.
 
+## 2.27.0 — 2026-09-11 — Local multi-user auth
+
+Self-host Pinscope accounts (email + password) so several people can share a project. Invite collaborators by email from the project page — same flow as cloud, without Clerk.
+
+- [New] `AUTH_JWT_SECRET` enables register/login; first user is admin and inherits `users/local` projects.
+- [New] `/sign-in` and `/sign-up`; sidebar account menu. Set `NEXT_PUBLIC_AUTH_MODE=local` on the frontend build.
+- [Changed] Collaborator lookup works for local users; Clerk still used when its keys are set.
+
 ## 2.26.5 — 2026-09-11 — Prefer PCB nets for connectivity
 
 When a `.kicad_pcb` is present, pad nets from the board drive the design graph. Schematic geometry alone was inventing swapped rails (GND↔3V3) and floating pins on good KiCad 10 designs.
diff --git a/frontend/dockerfile b/frontend/dockerfile
index c62d239..f619651 100644
--- a/frontend/dockerfile
+++ b/frontend/dockerfile
@@ -4,6 +4,8 @@ WORKDIR /app
 
 ARG NEXT_PUBLIC_API_URL
 ENV NEXT_PUBLIC_API_URL=$NEXT_PUBLIC_API_URL
+ARG NEXT_PUBLIC_AUTH_MODE
+ENV NEXT_PUBLIC_AUTH_MODE=$NEXT_PUBLIC_AUTH_MODE
 
 COPY package*.json ./
 RUN npm ci
@@ -12,7 +14,7 @@ COPY . .
 
 ENV NEXT_TELEMETRY_DISABLED=1
 
-RUN echo "BUILD API URL=$NEXT_PUBLIC_API_URL"
+RUN echo "BUILD API URL=$NEXT_PUBLIC_API_URL AUTH_MODE=$NEXT_PUBLIC_AUTH_MODE"
 RUN npm run build
 
 FROM node:20-alpine
@@ -21,6 +23,8 @@ WORKDIR /app
 
 ARG NEXT_PUBLIC_API_URL
 ENV NEXT_PUBLIC_API_URL=$NEXT_PUBLIC_API_URL
+ARG NEXT_PUBLIC_AUTH_MODE
+ENV NEXT_PUBLIC_AUTH_MODE=$NEXT_PUBLIC_AUTH_MODE
 
 ENV NODE_ENV=production
 ENV NEXT_TELEMETRY_DISABLED=1
diff --git a/frontend/src/app/(app)/layout.tsx b/frontend/src/app/(app)/layout.tsx
index 71c4b7d..96f154a 100644
--- a/frontend/src/app/(app)/layout.tsx
+++ b/frontend/src/app/(app)/layout.tsx
@@ -2,6 +2,7 @@ import { TooltipProvider } from "@/components/ui/tooltip";
 import { Sidebar } from "@/components/layout/sidebar";
 import { CreditsProvider } from "@/components/billing/credits-context";
 import { RedditPixelMatchKeys } from "@/components/analytics/reddit-pixel-match-keys";
+import { AuthGate } from "@/components/layout/auth-gate";
 
 export default function AppLayout({
   children,
@@ -11,12 +12,14 @@ export default function AppLayout({
   return (
     <TooltipProvider>
       <CreditsProvider>
-        <div className="flex h-full">
-          <Sidebar />
-          <main className="flex-1 flex flex-col overflow-auto">
-            {children}
-          </main>
-        </div>
+        <AuthGate>
+          <div className="flex h-full">
+            <Sidebar />
+            <main className="flex-1 flex flex-col overflow-auto">
+              {children}
+            </main>
+          </div>
+        </AuthGate>
         <RedditPixelMatchKeys />
       </CreditsProvider>
     </TooltipProvider>
diff --git a/frontend/src/app/(marketing)/sign-in/page.tsx b/frontend/src/app/(marketing)/sign-in/page.tsx
new file mode 100644
index 0000000..a3face7
--- /dev/null
+++ b/frontend/src/app/(marketing)/sign-in/page.tsx
@@ -0,0 +1,86 @@
+"use client";
+
+import { FormEvent, useState } from "react";
+import Link from "next/link";
+import { useRouter } from "next/navigation";
+import { storeAuthToken } from "@/hooks/use-optional-auth";
+import { Button } from "@/components/ui/button";
+import { Input } from "@/components/ui/input";
+import { Label } from "@/components/ui/label";
+
+const API_BASE = process.env.NEXT_PUBLIC_API_URL ?? "";
+
+export default function SignInPage() {
+  const router = useRouter();
+  const [email, setEmail] = useState("");
+  const [password, setPassword] = useState("");
+  const [error, setError] = useState<string | null>(null);
+  const [busy, setBusy] = useState(false);
+
+  async function onSubmit(e: FormEvent) {
+    e.preventDefault();
+    setBusy(true);
+    setError(null);
+    try {
+      const res = await fetch(`${API_BASE}/api/auth/login`, {
+        method: "POST",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({ email, password }),
+      });
+      const data = await res.json().catch(() => ({}));
+      if (!res.ok) {
+        throw new Error(data.detail || "Sign in failed");
+      }
+      storeAuthToken(data.token);
+      router.replace("/");
+      router.refresh();
+    } catch (err) {
+      setError(err instanceof Error ? err.message : "Sign in failed");
+    } finally {
+      setBusy(false);
+    }
+  }
+
+  return (
+    <div className="mx-auto flex min-h-[70vh] max-w-md flex-col justify-center px-4 py-16">
+      <h1 className="font-display text-3xl tracking-tight">Sign in</h1>
+      <p className="mt-2 text-sm text-muted-foreground">
+        Pinscope account for this server. Invite collaborators from a project once they have an account.
+      </p>
+      <form onSubmit={onSubmit} className="mt-8 flex flex-col gap-4">
+        <div className="space-y-2">
+          <Label htmlFor="email">Email</Label>
+          <Input
+            id="email"
+            type="email"
+            autoComplete="email"
+            required
+            value={email}
+            onChange={(e) => setEmail(e.target.value)}
+          />
+        </div>
+        <div className="space-y-2">
+          <Label htmlFor="password">Password</Label>
+          <Input
+            id="password"
+            type="password"
+            autoComplete="current-password"
+            required
+            value={password}
+            onChange={(e) => setPassword(e.target.value)}
+          />
+        </div>
+        {error && <p className="text-sm text-destructive">{error}</p>}
+        <Button type="submit" disabled={busy}>
+          {busy ? "Signing in…" : "Sign in"}
+        </Button>
+      </form>
+      <p className="mt-6 text-sm text-muted-foreground">
+        No account?{" "}
+        <Link href="/sign-up" className="underline underline-offset-4">
+          Create one
+        </Link>
+      </p>
+    </div>
+  );
+}
diff --git a/frontend/src/app/(marketing)/sign-up/page.tsx b/frontend/src/app/(marketing)/sign-up/page.tsx
new file mode 100644
index 0000000..e0a6c6a
--- /dev/null
+++ b/frontend/src/app/(marketing)/sign-up/page.tsx
@@ -0,0 +1,104 @@
+"use client";
+
+import { FormEvent, useState } from "react";
+import Link from "next/link";
+import { useRouter } from "next/navigation";
+import { storeAuthToken } from "@/hooks/use-optional-auth";
+import { Button } from "@/components/ui/button";
+import { Input } from "@/components/ui/input";
+import { Label } from "@/components/ui/label";
+
+const API_BASE = process.env.NEXT_PUBLIC_API_URL ?? "";
+
+export default function SignUpPage() {
+  const router = useRouter();
+  const [name, setName] = useState("");
+  const [email, setEmail] = useState("");
+  const [password, setPassword] = useState("");
+  const [error, setError] = useState<string | null>(null);
+  const [busy, setBusy] = useState(false);
+
+  async function onSubmit(e: FormEvent) {
+    e.preventDefault();
+    setBusy(true);
+    setError(null);
+    try {
+      const res = await fetch(`${API_BASE}/api/auth/register`, {
+        method: "POST",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({
+          email,
+          password,
+          name: name.trim() || null,
+        }),
+      });
+      const data = await res.json().catch(() => ({}));
+      if (!res.ok) {
+        const detail = data.detail;
+        throw new Error(
+          typeof detail === "string" ? detail : "Could not create account",
+        );
+      }
+      storeAuthToken(data.token);
+      router.replace("/");
+      router.refresh();
+    } catch (err) {
+      setError(err instanceof Error ? err.message : "Could not create account");
+    } finally {
+      setBusy(false);
+    }
+  }
+
+  return (
+    <div className="mx-auto flex min-h-[70vh] max-w-md flex-col justify-center px-4 py-16">
+      <h1 className="font-display text-3xl tracking-tight">Create account</h1>
+      <p className="mt-2 text-sm text-muted-foreground">
+        First account on this server becomes admin and inherits existing local projects.
+      </p>
+      <form onSubmit={onSubmit} className="mt-8 flex flex-col gap-4">
+        <div className="space-y-2">
+          <Label htmlFor="name">Name</Label>
+          <Input
+            id="name"
+            autoComplete="name"
+            value={name}
+            onChange={(e) => setName(e.target.value)}
+          />
+        </div>
+        <div className="space-y-2">
+          <Label htmlFor="email">Email</Label>
+          <Input
+            id="email"
+            type="email"
+            autoComplete="email"
+            required
+            value={email}
+            onChange={(e) => setEmail(e.target.value)}
+          />
+        </div>
+        <div className="space-y-2">
+          <Label htmlFor="password">Password</Label>
+          <Input
+            id="password"
+            type="password"
+            autoComplete="new-password"
+            required
+            minLength={8}
+            value={password}
+            onChange={(e) => setPassword(e.target.value)}
+          />
+        </div>
+        {error && <p className="text-sm text-destructive">{error}</p>}
+        <Button type="submit" disabled={busy}>
+          {busy ? "Creating…" : "Create account"}
+        </Button>
+      </form>
+      <p className="mt-6 text-sm text-muted-foreground">
+        Already have an account?{" "}
+        <Link href="/sign-in" className="underline underline-offset-4">
+          Sign in
+        </Link>
+      </p>
+    </div>
+  );
+}
diff --git a/frontend/src/components/layout/auth-gate.tsx b/frontend/src/components/layout/auth-gate.tsx
new file mode 100644
index 0000000..f019577
--- /dev/null
+++ b/frontend/src/components/layout/auth-gate.tsx
@@ -0,0 +1,33 @@
+"use client";
+
+import { useEffect } from "react";
+import { usePathname, useRouter } from "next/navigation";
+import { useOptionalAuth, useOptionalUser } from "@/hooks/use-optional-auth";
+import { localAuthEnabled } from "@/lib/auth";
+
+/** When local auth is on, send unsigned users to /sign-in. */
+export function AuthGate({ children }: { children: React.ReactNode }) {
+  const router = useRouter();
+  const pathname = usePathname();
+  const { isSignedIn } = useOptionalAuth();
+  const { isLoaded } = useOptionalUser();
+
+  useEffect(() => {
+    if (!localAuthEnabled || !isLoaded) return;
+    if (!isSignedIn) {
+      const next = encodeURIComponent(pathname || "/");
+      router.replace(`/sign-in?next=${next}`);
+    }
+  }, [isLoaded, isSignedIn, pathname, router]);
+
+  if (!localAuthEnabled) return <>{children}</>;
+  if (!isLoaded) {
+    return (
+      <div className="flex flex-1 items-center justify-center text-sm text-muted-foreground">
+        Loading…
+      </div>
+    );
+  }
+  if (!isSignedIn) return null;
+  return <>{children}</>;
+}
diff --git a/frontend/src/components/layout/sidebar-auth.tsx b/frontend/src/components/layout/sidebar-auth.tsx
index 715c029..3e9aaf9 100644
--- a/frontend/src/components/layout/sidebar-auth.tsx
+++ b/frontend/src/components/layout/sidebar-auth.tsx
@@ -1,12 +1,59 @@
 "use client";
 
-// Open-core seam: the cloud/gateway build replaces this file with the Clerk
-// user button and live credit balance. The open-source build has neither.
+// Open-core seam: cloud/gateway replaces with Clerk user button + credits.
+// Local auth shows email and sign-out / sign-in links.
+
+import Link from "next/link";
+import { useOptionalAuth, useOptionalUser } from "@/hooks/use-optional-auth";
+import { authEnabled, localAuthEnabled } from "@/lib/auth";
+import { Button } from "@/components/ui/button";
 
 export function SidebarCredits() {
   return null;
 }
 
 export function SidebarUserButton() {
-  return null;
+  const { user, isLoaded } = useOptionalUser();
+  const { signOut, isSignedIn } = useOptionalAuth();
+
+  if (!authEnabled || !localAuthEnabled) {
+    return null;
+  }
+
+  if (!isLoaded) {
+    return <div className="px-2 text-xs text-muted-foreground">…</div>;
+  }
+
+  if (!isSignedIn || !user) {
+    return (
+      <div className="flex flex-col gap-1 px-1">
+        <Button asChild size="sm" variant="outline" className="w-full justify-start">
+          <Link href="/sign-in">Sign in</Link>
+        </Button>
+        <Button asChild size="sm" variant="ghost" className="w-full justify-start">
+          <Link href="/sign-up">Create account</Link>
+        </Button>
+      </div>
+    );
+  }
+
+  return (
+    <div className="flex flex-col gap-1 px-2 py-1">
+      <div className="truncate text-xs font-medium">{user.name || user.email}</div>
+      {user.email && user.name ? (
+        <div className="truncate text-[11px] text-muted-foreground">{user.email}</div>
+      ) : null}
+      <Button
+        size="sm"
+        variant="ghost"
+        className="h-7 justify-start px-0 text-xs text-muted-foreground"
+        onClick={() => {
+          signOut?.();
+          window.location.href = "/sign-in";
+        }}
+      >
+        Sign out
+      </Button>
+    </div>
+  );
 }
diff --git a/frontend/src/hooks/use-optional-auth.ts b/frontend/src/hooks/use-optional-auth.ts
index 522ba7d..8245fbd 100644
--- a/frontend/src/hooks/use-optional-auth.ts
+++ b/frontend/src/hooks/use-optional-auth.ts
@@ -1,12 +1,13 @@
 "use client";
 
 /**
- * Open-core seam: the cloud/gateway build replaces this file with wrappers
- * around Clerk's hooks. The open-source build always runs as the local
- * user, mirroring the backend: user_id "local", admin access granted
- * (backend is_admin() returns True when auth is disabled).
+ * Open-core seam: cloud/gateway replaces this with Clerk hooks.
+ * Self-host local mode uses Pinscope JWT in localStorage.
  */
 
+import { useCallback, useEffect, useState } from "react";
+import { authEnabled, localAuthEnabled, TOKEN_STORAGE_KEY } from "@/lib/auth";
+
 export interface AppUser {
   id: string;
   name: string | null;
@@ -17,6 +18,7 @@ export interface AppUser {
 export interface OptionalAuth {
   isSignedIn: boolean;
   getToken: () => Promise<string | null>;
+  signOut?: () => void;
 }
 
 export interface OptionalUser {
@@ -30,13 +32,130 @@ const LOCAL_USER: AppUser = {
   email: null,
   isAdmin: true,
 };
-const LOCAL_AUTH: OptionalAuth = { isSignedIn: true, getToken: async () => null };
-const LOCAL_USER_RESULT: OptionalUser = { user: LOCAL_USER, isLoaded: true };
+
+const API_BASE = process.env.NEXT_PUBLIC_API_URL ?? "";
+
+function readStoredToken(): string | null {
+  if (typeof window === "undefined") return null;
+  try {
+    return window.localStorage.getItem(TOKEN_STORAGE_KEY);
+  } catch {
+    return null;
+  }
+}
+
+export function storeAuthToken(token: string | null) {
+  if (typeof window === "undefined") return;
+  try {
+    if (token) window.localStorage.setItem(TOKEN_STORAGE_KEY, token);
+    else window.localStorage.removeItem(TOKEN_STORAGE_KEY);
+  } catch {
+    /* ignore */
+  }
+  window.dispatchEvent(new Event("pinscope-auth-changed"));
+}
 
 export function useOptionalAuth(): OptionalAuth {
-  return LOCAL_AUTH;
+  const [token, setToken] = useState<string | null>(null);
+  const [ready, setReady] = useState(!localAuthEnabled);
+
+  useEffect(() => {
+    if (!localAuthEnabled) {
+      setReady(true);
+      return;
+    }
+    const sync = () => setToken(readStoredToken());
+    sync();
+    setReady(true);
+    window.addEventListener("pinscope-auth-changed", sync);
+    window.addEventListener("storage", sync);
+    return () => {
+      window.removeEventListener("pinscope-auth-changed", sync);
+      window.removeEventListener("storage", sync);
+    };
+  }, []);
+
+  const getToken = useCallback(async () => {
+    if (localAuthEnabled) return readStoredToken();
+    return null;
+  }, []);
+
+  const signOut = useCallback(() => {
+    storeAuthToken(null);
+    setToken(null);
+  }, []);
+
+  if (!authEnabled) {
+    return { isSignedIn: true, getToken: async () => null };
+  }
+
+  if (localAuthEnabled) {
+    return {
+      isSignedIn: ready && Boolean(token),
+      getToken,
+      signOut,
+    };
+  }
+
+  // Clerk build replaces this file; open-core without local mode stays open.
+  return { isSignedIn: true, getToken: async () => null };
 }
 
 export function useOptionalUser(): OptionalUser {
-  return LOCAL_USER_RESULT;
+  const { isSignedIn, getToken } = useOptionalAuth();
+  const [user, setUser] = useState<AppUser | null>(authEnabled ? null : LOCAL_USER);
+  const [isLoaded, setIsLoaded] = useState(!localAuthEnabled);
+
+  useEffect(() => {
+    if (!authEnabled) {
+      setUser(LOCAL_USER);
+      setIsLoaded(true);
+      return;
+    }
+    if (!localAuthEnabled) {
+      setUser(LOCAL_USER);
+      setIsLoaded(true);
+      return;
+    }
+    let cancelled = false;
+    (async () => {
+      setIsLoaded(false);
+      const token = await getToken();
+      if (!token) {
+        if (!cancelled) {
+          setUser(null);
+          setIsLoaded(true);
+        }
+        return;
+      }
+      try {
+        const res = await fetch(`${API_BASE}/api/auth/me`, {
+          headers: { Authorization: `Bearer ${token}` },
+        });
+        if (!res.ok) {
+          storeAuthToken(null);
+          if (!cancelled) setUser(null);
+          return;
+        }
+        const data = await res.json();
+        if (!cancelled) {
+          setUser({
+            id: data.user_id,
+            name: data.name ?? null,
+            email: data.email ?? null,
+            isAdmin: Boolean(data.is_admin),
+          });
+        }
+      } catch {
+        if (!cancelled) setUser(null);
+      } finally {
+        if (!cancelled) setIsLoaded(true);
+      }
+    })();
+    return () => {
+      cancelled = true;
+    };
+  }, [isSignedIn, getToken]);
+
+  return { user, isLoaded };
 }
diff --git a/frontend/src/lib/auth.ts b/frontend/src/lib/auth.ts
index fbbac60..20b5db3 100644
--- a/frontend/src/lib/auth.ts
+++ b/frontend/src/lib/auth.ts
@@ -1,13 +1,19 @@
 /**
  * Open-core auth switch.
  *
- * When NEXT_PUBLIC_CLERK_PUBLISHABLE_KEY is unset the app runs in local/OSS
- * mode: no ClerkProvider, pass-through middleware, a stubbed signed-in
- * "local" user (matching the backend's LOCAL_DEV_USER), and all credits /
- * billing UI hidden. Pairs with BILLING_ENABLED=false on the backend —
- * mixed modes (key set but billing off, or the inverse) are unsupported.
+ * - Clerk: NEXT_PUBLIC_CLERK_PUBLISHABLE_KEY set (cloud build).
+ * - Local: NEXT_PUBLIC_AUTH_MODE=local (self-host Pinscope accounts).
+ * - Off: neither — signed-in stub user "local", matching backend.
  *
- * NEXT_PUBLIC_* vars are inlined at build time, so this is a build-time
- * constant — changing it requires a rebuild / dev-server restart.
+ * NEXT_PUBLIC_* vars are inlined at build time.
  */
-export const authEnabled = Boolean(process.env.NEXT_PUBLIC_CLERK_PUBLISHABLE_KEY);
+export const authEnabled = Boolean(
+  process.env.NEXT_PUBLIC_CLERK_PUBLISHABLE_KEY ||
+    process.env.NEXT_PUBLIC_AUTH_MODE === "local",
+);
+
+export const localAuthEnabled =
+  process.env.NEXT_PUBLIC_AUTH_MODE === "local" &&
+  !process.env.NEXT_PUBLIC_CLERK_PUBLISHABLE_KEY;
+
+export const TOKEN_STORAGE_KEY = "pinscope_token";
diff --git a/scripts/update-pinscope.sh b/scripts/update-pinscope.sh
index 9ecf8ba..2d0b33b 100755
--- a/scripts/update-pinscope.sh
+++ b/scripts/update-pinscope.sh
@@ -118,6 +118,13 @@ upsert_env NEXT_PUBLIC_API_URL "$SITE" .env
 # JSON list — keep it a single line so docker compose / pydantic-settings parse it.
 upsert_env CORS_ORIGINS "[\"$SITE\"]" .env
 
+# Self-host multi-user auth (Pinscope accounts). Generate a secret once if missing.
+if [[ -z "$(read_env AUTH_JWT_SECRET .env || true)" ]]; then
+  log "Generating AUTH_JWT_SECRET for local multi-user auth"
+  upsert_env AUTH_JWT_SECRET "$(openssl rand -hex 32)" .env
+fi
+upsert_env NEXT_PUBLIC_AUTH_MODE "local" .env
+
 KEY="$(read_env DEEPSEEK_API_KEY .env || true)"
 if [[ -z "$KEY" || "$KEY" == "sk-..." ]]; then
   die "Set a real DEEPSEEK_API_KEY in $ROOT/.env before updating."
diff --git a/tests/test_local_auth.py b/tests/test_local_auth.py
new file mode 100644
index 0000000..a441ee2
--- /dev/null
+++ b/tests/test_local_auth.py
@@ -0,0 +1,61 @@
+"""Local Pinscope auth — users, JWT, email lookup (no FastAPI required)."""
+
+from __future__ import annotations
+
+import asyncio
+from pathlib import Path
+
+import pytest
+
+
+@pytest.fixture()
+def auth_env(tmp_path: Path, monkeypatch: pytest.MonkeyPatch):
+    from backend.config import settings
+
+    monkeypatch.setattr(settings, "auth_jwt_secret", "test-secret-not-for-prod")
+    monkeypatch.setattr(settings, "data_dir", tmp_path)
+    monkeypatch.setattr(settings, "clerk_secret_key", "")
+    monkeypatch.setattr(settings, "clerk_jwks_url", "")
+    monkeypatch.setattr(settings, "auth_admin_emails", "")
+    return tmp_path
+
+
+def test_create_user_and_authenticate(auth_env: Path):
+    from backend.services import local_users
+
+    user = local_users.create_user("a@example.com", "password12", "Ada")
+    assert user.is_admin is True
+    assert local_users.authenticate("a@example.com", "password12")
+    assert local_users.authenticate("a@example.com", "wrong") is None
+    assert local_users.find_by_email("a@example.com").user_id == user.user_id
+
+
+def test_second_user_not_admin(auth_env: Path):
+    from backend.services import local_users
+    from backend.services.user_directory import find_user_id_by_email
+
+    local_users.create_user("owner@example.com", "password12", "Owner")
+    mate = local_users.create_user("mate@example.com", "password12", "Mate")
+    assert mate.is_admin is False
+    uid = asyncio.run(find_user_id_by_email("mate@example.com"))
+    assert uid == mate.user_id
+
+
+def test_migrate_local_projects_on_first_register(auth_env: Path):
+    from backend.services import local_users
+
+    proj = auth_env / "users" / "local" / "projects" / "abc123"
+    proj.mkdir(parents=True)
+    (proj / "meta.json").write_text('{"id":"abc123","name":"Old"}\n')
+
+    user = local_users.create_user("first@example.com", "password12")
+    assert (auth_env / "users" / user.user_id / "projects" / "abc123").is_dir()
+    assert not (auth_env / "users" / "local" / "projects" / "abc123").exists()
+
+
+def test_duplicate_email_rejected(auth_env: Path):
+    from backend.services import local_users
+
+    local_users.create_user("a@example.com", "password12")
+    with pytest.raises(ValueError, match="already exists"):
+        local_users.create_user("a@example.com", "password12")