diff --git a/src-tauri/src/launcher.rs b/src-tauri/src/launcher.rs
index da2d9ca..7e893c9 100644
--- a/src-tauri/src/launcher.rs
+++ b/src-tauri/src/launcher.rs
@@ -1936,9 +1936,14 @@ impl Launcher {
       return Ok(());
     }
     self.log(app, "info", format!("Installing the web client's dependencies in {}", web.display()));
+    let node_dir = crate::nodejs::find();
     let status = tauri::async_runtime::spawn_blocking(move || {
       let mut cmd = std::process::Command::new("cmd");
       cmd.arg("/c").arg("npm").arg("install").current_dir(&web);
+      // Found, not assumed on PATH: right after ensure_node installed it, it is not.
+      if let Some(dir) = &node_dir {
+        cmd.env("PATH", crate::nodejs::path_with(dir));
+      }
       #[cfg(windows)]
       stack::give_console(&mut cmd);
       cmd.status()
@@ -1952,7 +1957,56 @@ impl Launcher {
     Ok(())
   }
 
+  /// Node.js for this run's web client, installed through winget when this PC has none.
+  ///
+  /// A dev drive moves between PCs, and the web client needs Node.js on whichever one it
+  /// lands on - without it the launch failed with npm's bare "exit code: 1". winget runs in
+  /// a console of its own: the install shows its progress there, Windows asks for
+  /// permission, and a failure (no network, usually) leaves its reason on screen.
+  async fn ensure_node(&self, app: &AppHandle) -> Result<(), String> {
+    if crate::nodejs::find().is_some() {
+      return Ok(());
+    }
+    self.log(
+      app,
+      "warn",
+      format!(
+        "Node.js is not installed, and the web client runs on it: installing Node.js LTS with winget ({}). Windows may ask for permission.",
+        crate::nodejs::WINGET_ID
+      ),
+    );
+    let status = tauri::async_runtime::spawn_blocking(|| {
+      let mut cmd = crate::nodejs::winget_command();
+      #[cfg(windows)]
+      stack::give_console(&mut cmd);
+      cmd.status()
+    })
+    .await
+    .map_err(|e| format!("could not run winget: {e}"))?;
+    // Judged by what is on disk afterwards, not by winget's exit code: "already installed"
+    // and "no newer version" are non-zero too, and both leave a working Node.js.
+    if let Some(dir) = crate::nodejs::find() {
+      self.log(app, "info", format!("Node.js is installed in {}.", dir.display()));
+      return Ok(());
+    }
+    let manual = "Install Node.js LTS from https://nodejs.org, then launch again.";
+    Err(match status {
+      Err(e) => format!("Node.js is not installed, and winget could not be started ({e}). {manual}"),
+      Ok(s) => format!(
+        "Node.js is not installed, and installing it with winget did not work ({s}); its window says why - no network is the usual reason. {manual}"
+      ),
+    })
+  }
+
   async fn run_stack(&self, app: &AppHandle, config: StackConfig) {
+    // Before the build too, which runs `npm install` for the web client.
+    if config.runs_web() {
+      if let Err(message) = self.ensure_node(app).await {
+        self.log(app, "error", message.clone());
+        self.finish(app, Some(message)).await;
+        return;
+      }
+    }
     // Asked for, and only in dev: a Launch that quietly took twenty minutes to compile
     // would be a worse surprise than a stale binary.
     if config.dev_engine.is_some() && self.inner.lock().await.settings.dev_build {
diff --git a/src-tauri/src/lib.rs b/src-tauri/src/lib.rs
index ba602b7..bbe6869 100644
--- a/src-tauri/src/lib.rs
+++ b/src-tauri/src/lib.rs
@@ -8,6 +8,7 @@ mod install;
 mod launcher;
 mod localdb;
 mod market;
+mod nodejs;
 mod prune;
 mod settings;
 mod site;
diff --git a/src-tauri/src/nodejs.rs b/src-tauri/src/nodejs.rs
new file mode 100644
index 0000000..e655a8e
--- /dev/null
+++ b/src-tauri/src/nodejs.rs
@@ -0,0 +1,133 @@
+//! Node.js for dev mode's web client: where it is, and installing it when it is not.
+//!
+//! The web client runs under `npm run dev` in the checkout's `_WEB`, so a dev PC without
+//! Node.js failed its launch with nothing but "stopped while starting (exit code: 1)": npm
+//! was not there to say anything. Seen on a fresh PC, and again when the dev drive moved to
+//! another one.
+
+use std::ffi::{OsStr, OsString};
+use std::path::{Path, PathBuf};
+use std::process::Command;
+
+/// The winget package: Node.js LTS, which the web client's Vite accepts (18, or 20 and up).
+pub const WINGET_ID: &str = "OpenJS.NodeJS.LTS";
+
+/// Folders that may hold npm, in the order they are tried: this process's PATH, then where
+/// the Node.js installer puts it. The second is what makes an install usable at once: the
+/// installer adds its folder to the SYSTEM PATH, which a process already running - this
+/// launcher - never sees until it is restarted.
+fn candidates(path_var: Option<&OsStr>, program_files: Option<&OsStr>) -> Vec<PathBuf> {
+  let mut dirs: Vec<PathBuf> = path_var.map(|p| std::env::split_paths(p).collect()).unwrap_or_default();
+  if let Some(program_files) = program_files {
+    dirs.push(Path::new(program_files).join("nodejs"));
+  }
+  dirs
+}
+
+/// The folder holding both `node.exe` and `npm.cmd`, from the given PATH and Program Files.
+/// Both, because npm is a script node runs: an `npm.cmd` left beside no `node.exe` (a
+/// half-removed install) fails exactly like no npm at all.
+pub fn find_in(path_var: Option<&OsStr>, program_files: Option<&OsStr>) -> Option<PathBuf> {
+  candidates(path_var, program_files)
+    .into_iter()
+    .find(|dir| dir.join("node.exe").is_file() && dir.join("npm.cmd").is_file())
+}
+
+/// Node.js on this PC, if any.
+pub fn find() -> Option<PathBuf> {
+  find_in(std::env::var_os("PATH").as_deref(), std::env::var_os("ProgramFiles").as_deref())
+}
+
+/// A PATH for a child that runs npm: `node_dir` first, then this process's own.
+pub fn path_with(node_dir: &Path) -> OsString {
+  let rest = std::env::var_os("PATH").unwrap_or_default();
+  let dirs = std::iter::once(node_dir.to_path_buf()).chain(std::env::split_paths(&rest));
+  // Only fails on a folder name holding the separator itself, which no real PATH entry has.
+  std::env::join_paths(dirs).unwrap_or(rest)
+}
+
+/// `winget install` for Node.js LTS. Through `cmd` because winget is an app-execution alias
+/// in WindowsApps, which cmd resolves the way a developer's own prompt would. No `--silent`
+/// on purpose: the console it runs in is the only place its progress and its reason for
+/// failing (no network, no winget source) are ever shown.
+pub fn winget_command() -> Command {
+  let mut cmd = Command::new("cmd");
+  cmd.args([
+    "/c",
+    "winget",
+    "install",
+    "--id",
+    WINGET_ID,
+    "--exact",
+    "--source",
+    "winget",
+    "--accept-package-agreements",
+    "--accept-source-agreements",
+  ]);
+  cmd
+}
+
+#[cfg(test)]
+mod tests {
+  use super::*;
+
+  /// A throwaway folder, optionally holding the two files a Node.js install has.
+  fn folder(with_node: bool, with_npm: bool) -> PathBuf {
+    let dir = std::env::temp_dir().join(format!("odian-nodejs-{}", uuid::Uuid::new_v4()));
+    std::fs::create_dir_all(&dir).unwrap();
+    if with_node {
+      std::fs::write(dir.join("node.exe"), b"").unwrap();
+    }
+    if with_npm {
+      std::fs::write(dir.join("npm.cmd"), b"").unwrap();
+    }
+    dir
+  }
+
+  #[test]
+  fn node_is_found_on_path_first() {
+    let (on_path, program_files) = (folder(true, true), folder(false, false));
+    std::fs::create_dir_all(program_files.join("nodejs")).unwrap();
+    let path = std::env::join_paths([folder(false, false), on_path.clone()]).unwrap();
+    assert_eq!(find_in(Some(&path), Some(program_files.as_os_str())), Some(on_path));
+  }
+
+  #[test]
+  fn a_fresh_install_is_found_where_the_installer_puts_it() {
+    // What winget has just done: Program Files\nodejs exists, and this process's PATH -
+    // read when the launcher started - does not name it.
+    let program_files = folder(false, false);
+    let nodejs = program_files.join("nodejs");
+    std::fs::create_dir_all(&nodejs).unwrap();
+    std::fs::write(nodejs.join("node.exe"), b"").unwrap();
+    std::fs::write(nodejs.join("npm.cmd"), b"").unwrap();
+    let path = std::env::join_paths([folder(false, false)]).unwrap();
+    assert_eq!(find_in(Some(&path), Some(program_files.as_os_str())), Some(nodejs));
+  }
+
+  #[test]
+  fn npm_without_node_is_no_node() {
+    let half = folder(false, true);
+    let path = std::env::join_paths([half]).unwrap();
+    assert_eq!(find_in(Some(&path), None), None);
+    assert_eq!(find_in(None, None), None);
+  }
+
+  #[test]
+  fn the_child_path_puts_node_first() {
+    let dir = PathBuf::from(r"C:\Program Files\nodejs");
+    let path = path_with(&dir);
+    assert_eq!(std::env::split_paths(&path).next(), Some(dir));
+  }
+
+  #[test]
+  fn winget_installs_node_lts_without_asking_on_the_console() {
+    let cmd = winget_command();
+    let args: Vec<String> = cmd.get_args().map(|a| a.to_string_lossy().into_owned()).collect();
+    assert_eq!(&args[..3], ["/c", "winget", "install"]);
+    assert!(args.windows(2).any(|w| w == ["--id", WINGET_ID]), "{args:?}");
+    // Unanswered, these two prompts wait on the console forever on a first run.
+    assert!(args.iter().any(|a| a == "--accept-package-agreements"));
+    assert!(args.iter().any(|a| a == "--accept-source-agreements"));
+  }
+}
diff --git a/src-tauri/src/stack.rs b/src-tauri/src/stack.rs
index 183f82e..985dfd9 100644
--- a/src-tauri/src/stack.rs
+++ b/src-tauri/src/stack.rs
@@ -613,9 +613,11 @@ async fn start_client(config: &StackConfig, emit: Emit<'_>, running: &mut Runnin
 ///
 /// Its own function so the argument list is testable: a wrong flag here would only show as
 /// a failed launch, and the bare `--` matters - without it npm keeps the rest for itself
-/// instead of passing it to Vite.
-fn web_command(dir: &Path) -> Command {
+/// instead of passing it to Vite. `node_dir` goes first on its PATH: right after the
+/// launcher installed Node.js, this process's own PATH does not name it yet.
+fn web_command(dir: &Path, node_dir: &Path) -> Command {
   let mut web = Command::new("cmd");
+  web.env("PATH", crate::nodejs::path_with(node_dir));
   // --strictPort because without it Vite quietly takes the next free port, and the address
   // the launcher opens - and prints - would then be somebody else's server.
   web
@@ -659,7 +661,16 @@ async fn start_web(
       format!("{} has no node_modules yet. Tick \"Build it first, every launch\" in Settings, which installs them, or run `npm install` there once.", dir.display()),
     ));
   }
-  let mut web = web_command(&dir);
+  // The launcher installs Node.js before a web run starts (Launcher::ensure_node), so this
+  // only guards a PC where that was refused - and says so, instead of npm's bare exit 1.
+  let Some(node_dir) = crate::nodejs::find() else {
+    return Err(failed(
+      emit,
+      Component::Web,
+      format!("Node.js is not installed, and the web client runs on it. Install Node.js LTS (winget install {}), then launch again.", crate::nodejs::WINGET_ID),
+    ));
+  };
+  let mut web = web_command(&dir, &node_dir);
   give_console(&mut web);
   let child = running.spawn(Component::Web, &mut web).map_err(|e| failed(emit, Component::Web, e))?;
   // A cold start compiles Cesium, so this is patient where the others are not.
@@ -1401,7 +1412,7 @@ mod tests {
     // Checked as ARGUMENTS rather than by reading the binary: these are short literals that
     // a release build merges away, so "is the flag in the .exe" answers nothing. A wrong
     // flag here would surface only as a failed launch.
-    let cmd = web_command(Path::new(r"E:\dev\ODIAN_Engine\_WEB"));
+    let cmd = web_command(Path::new(r"E:\dev\ODIAN_Engine\_WEB"), Path::new(r"C:\Program Files\nodejs"));
     let args: Vec<String> = cmd.get_args().map(|a| a.to_string_lossy().into_owned()).collect();
     assert_eq!(args, ["/c", "npm", "run", "dev", "--", "--port", "5173", "--strictPort"]);
     // The bare `--` is load-bearing: without it npm eats the flags instead of passing them on.
@@ -1418,7 +1429,7 @@ mod tests {
   fn the_web_draws_its_map_from_this_stacks_tile_server() {
     // Offline, the public tile host is unreachable; this stack's tile server still has
     // the PC's installed tiles. _WEB's vite.config.ts reads this variable.
-    let cmd = web_command(Path::new(r"E:\dev\ODIAN_Engine\_WEB"));
+    let cmd = web_command(Path::new(r"E:\dev\ODIAN_Engine\_WEB"), Path::new(r"C:\Program Files\nodejs"));
     let tiles = cmd
       .get_envs()
       .find(|(key, _)| *key == "ODIAN_TILE_SERVER_URL")
@@ -1427,6 +1438,20 @@ mod tests {
     assert_eq!(tiles.as_deref(), Some("http://127.0.0.1:18081"));
   }
 
+  #[test]
+  fn npm_finds_the_node_the_launcher_found() {
+    // Right after the launcher installs Node.js, its own PATH does not name it yet; npm
+    // runs with the found folder first, so the launch goes on without a restart.
+    let node = Path::new(r"C:\Program Files\nodejs");
+    let cmd = web_command(Path::new(r"E:\dev\ODIAN_Engine\_WEB"), node);
+    let path = cmd
+      .get_envs()
+      .find(|(key, _)| *key == "PATH")
+      .and_then(|(_, value)| value)
+      .expect("web_command sets PATH");
+    assert_eq!(std::env::split_paths(path).next().as_deref(), Some(node));
+  }
+
   #[test]
   fn a_query_value_cannot_end_its_own_parameter() {
     // The address is built here, but the operator name comes from a text field.