diff --git a/backend/src/main.rs b/backend/src/main.rs
index 24ea8f8..68089bf 100644
--- a/backend/src/main.rs
+++ b/backend/src/main.rs
@@ -55,6 +55,101 @@ async fn main() {
     }
 }
 
+#[cfg(test)]
+mod security_headers_tests {
+    use super::add_security_headers;
+    use axum::body::Body;
+    use axum::http::{header, Request, StatusCode};
+    use axum::middleware;
+    use axum::response::Response;
+    use axum::routing::get;
+    use axum::Router;
+    use tower::ServiceExt;
+
+    #[tokio::test]
+    async fn security_headers_are_added_by_default() {
+        let app = Router::new()
+            .route("/api/ping", get(|| async { "ok" }))
+            .layer(middleware::map_response(add_security_headers));
+
+        let req = Request::builder()
+            .method("GET")
+            .uri("/api/ping")
+            .body(Body::empty())
+            .unwrap();
+        let res = app.oneshot(req).await.unwrap();
+        assert_eq!(res.status(), StatusCode::OK);
+
+        assert_eq!(
+            res.headers()
+                .get("x-content-type-options")
+                .and_then(|v| v.to_str().ok()),
+            Some("nosniff")
+        );
+        assert_eq!(
+            res.headers()
+                .get("x-frame-options")
+                .and_then(|v| v.to_str().ok()),
+            Some("DENY")
+        );
+        assert_eq!(
+            res.headers()
+                .get("referrer-policy")
+                .and_then(|v| v.to_str().ok()),
+            Some("no-referrer")
+        );
+        assert_eq!(
+            res.headers()
+                .get("permissions-policy")
+                .and_then(|v| v.to_str().ok()),
+            Some("camera=(), microphone=(), geolocation=()")
+        );
+        assert_eq!(
+            res.headers()
+                .get("x-permitted-cross-domain-policies")
+                .and_then(|v| v.to_str().ok()),
+            Some("none")
+        );
+    }
+
+    #[tokio::test]
+    async fn security_headers_do_not_override_explicit_headers() {
+        let app = Router::new()
+            .route(
+                "/api/ping",
+                get(|| async {
+                    Response::builder()
+                        .status(StatusCode::OK)
+                        .header("x-frame-options", "SAMEORIGIN")
+                        .header(header::REFERRER_POLICY, "strict-origin")
+                        .body(Body::from("ok"))
+                        .unwrap()
+                }),
+            )
+            .layer(middleware::map_response(add_security_headers));
+
+        let req = Request::builder()
+            .method("GET")
+            .uri("/api/ping")
+            .body(Body::empty())
+            .unwrap();
+        let res = app.oneshot(req).await.unwrap();
+
+        assert_eq!(
+            res.headers()
+                .get("x-frame-options")
+                .and_then(|v| v.to_str().ok()),
+            Some("SAMEORIGIN")
+        );
+        assert_eq!(
+            res.headers()
+                .get(header::REFERRER_POLICY)
+                .and_then(|v| v.to_str().ok()),
+            Some("strict-origin")
+        );
+    }
+}
+
 async fn run() -> Result<(), StartupError> {
     dotenvy::dotenv().ok();
 
@@ -349,6 +444,20 @@ async fn add_security_headers(mut res: Response) -> Response {
         );
     }
 
+    if !headers.contains_key("permissions-policy") {
+        headers.insert(
+            HeaderName::from_static("permissions-policy"),
+            HeaderValue::from_static("camera=(), microphone=(), geolocation=()"),
+        );
+    }
+
+    if !headers.contains_key("x-permitted-cross-domain-policies") {
+        headers.insert(
+            HeaderName::from_static("x-permitted-cross-domain-policies"),
+            HeaderValue::from_static("none"),
+        );
+    }
+
     res
 }
 
diff --git a/docs/admin/installation.md b/docs/admin/installation.md
index 4c79ae0..9253c6b 100644
--- a/docs/admin/installation.md
+++ b/docs/admin/installation.md
@@ -26,6 +26,7 @@ cp compose/.env.production.example compose/.env.production
 ```
 
 Required settings:
+
 - `POSTGRES_PASSWORD` - Strong database password
 - `JWT_SECRET` - Random 64+ character string
 
@@ -38,8 +39,8 @@ podman-compose --env-file .env.production -f production.yml up -d
 
 ### 4. Access
 
-- Frontend: http://localhost:4321
-- Backend API: http://localhost:3000
+- Frontend: <http://localhost:4321>
+- Backend API: <http://localhost:3000>
 
 ## Manual Installation
 
@@ -76,19 +77,21 @@ node ./dist/server/entry.mjs
 
 ## Configuration Files
 
-| File | Purpose |
-|------|---------|
-| `compose/production.yml` | Production container deployment |
-| `compose/demo.yml` | Demo instance deployment |
-| `compose/.env.production.example` | Environment template |
-| `backend/.env` | Backend configuration |
+|File|Purpose|
+|---|---|
+|`compose/production.yml`|Production container deployment|
+|`compose/demo.yml`|Demo instance deployment|
+|`compose/.env.production.example`|Environment template|
+|`backend/.env`|Backend configuration|
 
 ## Reverse Proxy
 
 For production, use a reverse proxy (nginx, Caddy) with:
+
 - HTTPS termination
 - WebSocket support (for real-time features)
 - Proper headers
+- HSTS (set on the reverse proxy)
 
 Example nginx config:
 
@@ -107,12 +110,16 @@ server {
         proxy_set_header Connection "upgrade";
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;
+        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+        proxy_set_header X-Forwarded-Proto $scheme;
     }
 
     location /api {
         proxy_pass http://127.0.0.1:3000;
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;
+        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+        proxy_set_header X-Forwarded-Proto $scheme;
     }
 }
 ```
diff --git a/docs/admin/security.md b/docs/admin/security.md
index b70c75e..af11968 100644
--- a/docs/admin/security.md
+++ b/docs/admin/security.md
@@ -33,6 +33,18 @@ Always use HTTPS in production:
 - Configure reverse proxy for TLS termination
 - Enable HSTS headers
 
+### Security Headers
+
+The backend sets a small set of security headers on responses by default:
+
+- `X-Content-Type-Options: nosniff`
+- `X-Frame-Options: DENY`
+- `Referrer-Policy: no-referrer`
+- `Permissions-Policy: camera=(), microphone=(), geolocation=()`
+- `X-Permitted-Cross-Domain-Policies: none`
+
+Set `Strict-Transport-Security` (HSTS) on your reverse proxy, because the backend does not know whether requests arrived via HTTPS.
+
 ### CORS
 
 Restrict CORS in production: