diff --git a/CLAUDE.md b/CLAUDE.md
index f0e6ca8..0827b6b 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -16,7 +16,8 @@ editing Nix expressions.
 
 This project uses `just` (see `justfile`) and Nix directly.
 
-- `just build-vm` — cleans previous artifacts and builds the test VM (`nixosConfigurations.test`) via `nom build`.
+- `just build-vm [proxy]` — cleans previous artifacts and builds the test VM (`nixosConfigurations.test-<proxy>`)
+  via `nom build`. `proxy` is `nginx` (default) or `caddy`.
 - `just boot-vm` — boots the built VM (`result/bin/run-nixos-vm`) in the current terminal. Serves Invoice Ninja on
   `localhost:8080` (see `QEMU_NET_OPTS` in the `justfile`) with root login `toor`.
 - `just clean` — removes `result`/`nixos.qcow2` and kills any running `qemu` process.
@@ -28,10 +29,12 @@ This project uses `just` (see `justfile`) and Nix directly.
 ### `tests/`
 
 - `common.nix` — the shared `services.invoiceninja` config used by both the interactive VM and the automated test:
-  imports the module, enables nginx, and points at the checked-in test fixtures (`invoice_ninja_test_password`,
-  `test.env`).
-- `default.nix` — the interactive VM config (`nixosConfigurations.test` in `flake.nix`), used for manual,
-  click-around verification via `just build-vm` / `just boot-vm`. Adds the qemu-guest profile, a root login, and
+  imports the module and points at the checked-in test fixtures (`invoice_ninja_test_password`, `test.env`). It's a
+  function taking `{ proxyServer ? "nginx" }` so callers can pick which proxy backend to test.
+- `default.nix` — the interactive VM config (`nixosConfigurations.test-nginx`/`test-caddy` in `flake.nix`), used
+  for manual, click-around verification via `just build-vm [proxy]` / `just boot-vm`. It's also a function taking
+  `{ proxyServer ? "nginx" }`, forwarded straight through to `common.nix`, so `flake.nix` can instantiate one
+  `nixosConfigurations` entry per proxy backend. Adds the qemu-guest profile, a root login, and
   `nixpkgs.config.allowUnfree = true` (required to build `pkgs.chromium`). It also sets a dummy `fileSystems."/"`
   and disables `boot.loader.grub` purely to satisfy NixOS's built-in assertions when `nix flake check` evaluates
   `config.system.build.toplevel` directly — the qemu-vm module overrides both with a tmpfs root and direct kernel
@@ -39,12 +42,15 @@ This project uses `just` (see `justfile`) and Nix directly.
   unused.
 - `nixos-test.nix` — the automated test (`pkgs.testers.nixosTest`, exposed as `checks.<system>.invoiceninja` in
   `flake.nix`). Builds its own `pkgs` (with `allowUnfree` baked in — `nixosTest` forbids setting `nixpkgs.config`
-  on a node once `pkgs` is externally supplied) and boots a VM with `common.nix`, then: waits for
-  mysql/redis/phpfpm/queue-worker/nginx to be active, checks the `invoiceninja-data-setup` marker files
-  (`.initial-migration`, `.db-seeded`, `.admin-created`) to confirm the one-time setup actually completed (not just
-  that the oneshot unit exited), curls `/` for the app shell, exercises the `invoiceninja-manage` wrapper, and logs
-  in via `/api/v1/login` using the test admin credentials as an end-to-end check that migrations/seeding/account
-  creation all worked. This is the only automated test in the repo — there is no separate unit-test suite.
+  on a node once `pkgs` is externally supplied) and boots two nodes from `common.nix` — one with
+  `proxyServer = "nginx"`, one with `proxyServer = "caddy"` — so both proxy backends get exercised. The shared
+  assertion suite (factored into a `check_invoiceninja(machine, proxy_unit)` function in the test script) runs
+  against each node: waits for mysql/redis/phpfpm/queue-worker/proxy to be active, checks the
+  `invoiceninja-data-setup` marker files (`.initial-migration`, `.db-seeded`, `.admin-created`) to confirm the
+  one-time setup actually completed (not just that the oneshot unit exited), curls `/` for the app shell, exercises
+  the `invoiceninja-manage` wrapper, and logs in via `/api/v1/login` using the test admin credentials as an
+  end-to-end check that migrations/seeding/account creation all worked. This is the only automated test in the
+  repo — there is no separate unit-test suite.
 
 ## Architecture
 
@@ -108,8 +114,9 @@ expect Nix to report the correct hash on a failed build (or use `nix-prefetch`/`
 ### `flake.nix`
 
 Standard flake shape: `overlays.default` registers the package, `packages.<system>.invoiceninja` exposes it,
-`nixosModules` re-exports `nixos-module/default.nix`, and `nixosConfigurations.test` builds the VM defined in
-`tests/`. Only `x86_64-linux` is currently supported.
+`nixosModules` re-exports `nixos-module/default.nix`, and `nixosConfigurations.test-nginx`/`test-caddy` each build
+the VM defined in `tests/default.nix` with the corresponding `proxyServer`. Only `x86_64-linux` is currently
+supported.
 
 ## Conventions
 
diff --git a/flake.nix b/flake.nix
index a5352f4..e639cfd 100644
--- a/flake.nix
+++ b/flake.nix
@@ -20,9 +20,15 @@
       );
     in
     rec {
-      nixosConfigurations.test = nixpkgs.lib.nixosSystem {
-        system = "x86_64-linux";
-        modules = [ ./tests ];
+      nixosConfigurations = {
+        test-nginx = nixpkgs.lib.nixosSystem {
+          system = "x86_64-linux";
+          modules = [ (import ./tests/default.nix { proxyServer = "nginx"; }) ];
+        };
+        test-caddy = nixpkgs.lib.nixosSystem {
+          system = "x86_64-linux";
+          modules = [ (import ./tests/default.nix { proxyServer = "caddy"; }) ];
+        };
       };
 
       overlays.default = final: prev: { invoiceninja = final.callPackage ./package.nix { }; };
diff --git a/justfile b/justfile
index 470011f..b52cf94 100644
--- a/justfile
+++ b/justfile
@@ -18,10 +18,10 @@ clean:
     pkill qemu
     exit 0
 
-[doc('Build virtual machine for testing')]
+[doc('Build virtual machine for testing (proxy: nginx or caddy)')]
 [group('main')]
-build-vm: clean
-    nom build ".#nixosConfigurations.test.config.system.build.vm"
+build-vm proxy="nginx": clean
+    nom build ".#nixosConfigurations.test-{{proxy}}.config.system.build.vm"
 
 [doc('Run virtual machine in current terminal')]
 [group('main')]
diff --git a/tests/common.nix b/tests/common.nix
index 39a089a..5f9c84f 100644
--- a/tests/common.nix
+++ b/tests/common.nix
@@ -1,3 +1,4 @@
+{ proxyServer ? "nginx" }:
 { ... }:
 
 {
@@ -5,7 +6,7 @@
 
   services.invoiceninja = {
     enable = true;
-    proxy.server = "nginx";
+    proxy.server = proxyServer;
     adminAccount.passwordFile = ./invoice_ninja_test_password;
     secretFile = ./test.env;
     settings.APP_DEBUG = true;
diff --git a/tests/default.nix b/tests/default.nix
index 8f0c6f5..5c270d0 100644
--- a/tests/default.nix
+++ b/tests/default.nix
@@ -1,9 +1,10 @@
+{ proxyServer ? "nginx" }:
 { pkgs, modulesPath, ... }:
 
 {
   imports = [
     (modulesPath + "/profiles/qemu-guest.nix")
-    ./common.nix
+    (import ./common.nix { inherit proxyServer; })
   ];
 
   # Required to build pkgs.chromium, which the module pulls in for PDF generation.
diff --git a/tests/nixos-test.nix b/tests/nixos-test.nix
index d06d1e8..1590f3f 100644
--- a/tests/nixos-test.nix
+++ b/tests/nixos-test.nix
@@ -15,54 +15,61 @@ in
 pkgs.testers.nixosTest {
   name = "invoiceninja";
 
-  nodes.machine = {
-    imports = [ ./common.nix ];
+  nodes = {
+    nginx.imports = [ (import ./common.nix { proxyServer = "nginx"; }) ];
+    caddy.imports = [ (import ./common.nix { proxyServer = "caddy"; }) ];
   };
 
   testScript = ''
-    machine.start()
+    def check_invoiceninja(machine, proxy_unit):
+        machine.wait_for_unit("mysql.service")
+        machine.wait_for_unit("redis-invoiceninja.service")
+        machine.wait_for_unit("phpfpm-invoiceninja.service")
+        machine.wait_for_unit("invoiceninja-queue-worker.service")
+        machine.wait_for_unit(proxy_unit)
+        machine.wait_for_open_port(80)
 
-    machine.wait_for_unit("mysql.service")
-    machine.wait_for_unit("redis-invoiceninja.service")
-    machine.wait_for_unit("phpfpm-invoiceninja.service")
-    machine.wait_for_unit("invoiceninja-queue-worker.service")
-    machine.wait_for_unit("nginx.service")
-    machine.wait_for_open_port(80)
+        # phpfpm-invoiceninja/invoiceninja-queue-worker both Require= invoiceninja-data-setup,
+        # so systemd already waited for it to finish above. Confirm the one-time setup steps
+        # it guards actually completed, rather than just that the unit exited.
+        with subtest("one-time setup (migrate, seed, admin account) completed"):
+            machine.succeed("test -f /var/lib/invoiceninja/.initial-migration")
+            machine.succeed("test -f /var/lib/invoiceninja/.db-seeded")
+            machine.succeed("test -f /var/lib/invoiceninja/.admin-created")
 
-    # phpfpm-invoiceninja/invoiceninja-queue-worker both Require= invoiceninja-data-setup,
-    # so systemd already waited for it to finish above. Confirm the one-time setup steps
-    # it guards actually completed, rather than just that the unit exited.
-    with subtest("one-time setup (migrate, seed, admin account) completed"):
-        machine.succeed("test -f /var/lib/invoiceninja/.initial-migration")
-        machine.succeed("test -f /var/lib/invoiceninja/.db-seeded")
-        machine.succeed("test -f /var/lib/invoiceninja/.admin-created")
+        with subtest("application shell is served over HTTP"):
+            response = machine.succeed("curl -sf http://localhost/")
+            assert "Invoice Ninja" in response, f"unexpected response from /: {response}"
 
-    with subtest("application shell is served over HTTP"):
-        response = machine.succeed("curl -sf http://localhost/")
-        assert "Invoice Ninja" in response, f"unexpected response from /: {response}"
+        with subtest("web UI login page is served"):
+            # The UI is a client-side-routed React SPA, so curl (no JS) only sees the same
+            # index.html shell as "/" - this confirms the proxy/Laravel resolve the /login route
+            # to that shell instead of 404ing, which is what a browser needs before it can
+            # render the actual login form.
+            login_page = machine.succeed("curl -sf http://localhost/login")
+            assert "Invoice Ninja" in login_page, f"unexpected response from /login: {login_page}"
 
-    with subtest("web UI login page is served"):
-        # The UI is a client-side-routed React SPA, so curl (no JS) only sees the same
-        # index.html shell as "/" - this confirms nginx/Laravel resolve the /login route
-        # to that shell instead of 404ing, which is what a browser needs before it can
-        # render the actual login form.
-        login_page = machine.succeed("curl -sf http://localhost/login")
-        assert "Invoice Ninja" in login_page, f"unexpected response from /login: {login_page}"
+        with subtest("invoiceninja-manage wrapper can run artisan commands"):
+            machine.succeed("invoiceninja-manage migrate:status")
 
-    with subtest("invoiceninja-manage wrapper can run artisan commands"):
-        machine.succeed("invoiceninja-manage migrate:status")
+        with subtest("scheduler timer is enabled and schedule:run succeeds"):
+            # Without this, the app's dashboard reports "cron jobs are not enabled".
+            machine.succeed("systemctl is-active invoiceninja-scheduler.timer")
+            machine.succeed("systemctl start --wait invoiceninja-scheduler.service")
 
-    with subtest("scheduler timer is enabled and schedule:run succeeds"):
-        # Without this, the app's dashboard reports "cron jobs are not enabled".
-        machine.succeed("systemctl is-active invoiceninja-scheduler.timer")
-        machine.succeed("systemctl start --wait invoiceninja-scheduler.service")
+        with subtest("admin account can log in via the API"):
+            login_response = machine.succeed(
+                "curl -sf -X POST http://localhost/api/v1/login "
+                + "-H 'Content-Type: application/json' "
+                + "-d '{\"email\":\"${adminEmail}\",\"password\":\"${adminPassword}\"}'"
+            )
+            assert "${adminEmail}" in login_response, f"login did not succeed: {login_response}"
 
-    with subtest("admin account can log in via the API"):
-        login_response = machine.succeed(
-            "curl -sf -X POST http://localhost/api/v1/login "
-            + "-H 'Content-Type: application/json' "
-            + "-d '{\"email\":\"${adminEmail}\",\"password\":\"${adminPassword}\"}'"
-        )
-        assert "${adminEmail}" in login_response, f"login did not succeed: {login_response}"
+
+    nginx.start()
+    caddy.start()
+
+    check_invoiceninja(nginx, "nginx.service")
+    check_invoiceninja(caddy, "caddy.service")
   '';
 }