diff --git a/.gitignore b/.gitignore
index 1d70eaee9..7b0c7f127 100644
--- a/.gitignore
+++ b/.gitignore
@@ -10,3 +10,5 @@ target
 /windows.bazelrc
 /out
 node_modules
+.n2_db
+.ninja_log
diff --git a/Cargo.lock b/Cargo.lock
index 80623840a..d2378c2f5 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -160,6 +160,8 @@ dependencies = [
 name = "anki_i18n"
 version = "0.0.0"
 dependencies = [
+ "anki_io",
+ "anyhow",
  "fluent",
  "fluent-bundle",
  "fluent-syntax",
@@ -824,6 +826,8 @@ dependencies = [
 name = "configure"
 version = "0.0.0"
 dependencies = [
+ "anyhow",
+ "itertools",
  "ninja_gen",
  "workspace-hack",
 ]
@@ -2405,6 +2409,8 @@ checksum = "e4a24736216ec316047a1fc4252e27dabb04218aa4a3f37c6e7ddbf1f9782b54"
 name = "ninja_gen"
 version = "0.0.0"
 dependencies = [
+ "anki_io",
+ "anyhow",
  "camino",
  "globset",
  "itertools",
@@ -3397,6 +3403,7 @@ dependencies = [
  "itertools",
  "junction",
  "termcolor",
+ "which",
  "workspace-hack",
 ]
 
diff --git a/build/configure/Cargo.toml b/build/configure/Cargo.toml
index c51c864d1..ed362a738 100644
--- a/build/configure/Cargo.toml
+++ b/build/configure/Cargo.toml
@@ -9,5 +9,7 @@ license.workspace = true
 rust-version.workspace = true
 
 [dependencies]
+anyhow = "1.0.71"
+itertools = "0.10.5"
 ninja_gen = { "path" = "../ninja_gen" }
 workspace-hack = { version = "0.1", path = "../../tools/workspace-hack" }
diff --git a/build/configure/src/main.rs b/build/configure/src/main.rs
index 377b06c08..3f915db43 100644
--- a/build/configure/src/main.rs
+++ b/build/configure/src/main.rs
@@ -56,7 +56,7 @@ fn main() -> Result<()> {
 
     build.trailing_text = "default pylib qt\n".into();
 
-    build.write_build_file();
+    build.write_build_file()?;
 
     Ok(())
 }
diff --git a/build/configure/src/web.rs b/build/configure/src/web.rs
index 5179b6724..2b6a384b4 100644
--- a/build/configure/src/web.rs
+++ b/build/configure/src/web.rs
@@ -141,7 +141,10 @@ fn build_and_check_tslib(build: &mut Build) -> Result<()> {
             protos: inputs![glob!["proto/**/*.proto"]],
             include_dirs: &["proto"],
             out_dir: "out/ts/lib",
-            out_path_transform: |path| path.replace("proto/", "ts/lib/"),
+            out_path_transform: |path| {
+                path.replace("proto/", "ts/lib/")
+                    .replace("proto\\", "ts/lib\\")
+            },
             py_transform_script: "pylib/tools/markpure.py",
         },
     )?;
diff --git a/build/ninja_gen/Cargo.toml b/build/ninja_gen/Cargo.toml
index 87d074425..7f7079334 100644
--- a/build/ninja_gen/Cargo.toml
+++ b/build/ninja_gen/Cargo.toml
@@ -9,6 +9,8 @@ license.workspace = true
 rust-version.workspace = true
 
 [dependencies]
+anki_io = { version = "0.0.0", path = "../../rslib/io" }
+anyhow = "1.0.71"
 camino = "1.1.4"
 globset = "0.4.10"
 itertools = "0.10.5"
diff --git a/build/ninja_gen/src/build.rs b/build/ninja_gen/src/build.rs
index bac5a8b9c..5d4690c14 100644
--- a/build/ninja_gen/src/build.rs
+++ b/build/ninja_gen/src/build.rs
@@ -6,6 +6,7 @@ use std::collections::HashSet;
 use std::fmt::Write;
 
 use camino::Utf8PathBuf;
+use itertools::Itertools;
 
 use crate::action::BuildAction;
 use crate::archives::Platform;
@@ -266,11 +267,13 @@ impl BuildStatement<'_> {
     /// `existing_outputs`, and any subgroups.
     fn render_into(mut self, buf: &mut String) -> (Vec<String>, Vec<(String, Vec<String>)>) {
         let action_name = self.rule_name;
+        self.implicit_inputs.sort();
+        self.implicit_outputs.sort();
         let inputs_str = to_ninja_target_string(&self.explicit_inputs, &self.implicit_inputs);
         let outputs_str = to_ninja_target_string(&self.explicit_outputs, &self.implicit_outputs);
 
         writeln!(buf, "build {outputs_str}: {action_name} {inputs_str}").unwrap();
-        for (key, value) in self.variables {
+        for (key, value) in self.variables.iter().sorted() {
             writeln!(buf, "  {key} = {}", value).unwrap();
         }
         writeln!(buf).unwrap();
diff --git a/build/ninja_gen/src/render.rs b/build/ninja_gen/src/render.rs
index a34d248e3..14861ad8b 100644
--- a/build/ninja_gen/src/render.rs
+++ b/build/ninja_gen/src/render.rs
@@ -2,7 +2,11 @@
 // License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
 
 use std::fmt::Write;
-use std::fs::read_to_string;
+
+use anki_io::create_dir_all;
+use anki_io::write_file_if_changed;
+use anyhow::Result;
+use itertools::Itertools;
 
 use crate::archives::with_exe;
 use crate::input::space_separated;
@@ -18,7 +22,6 @@ impl Build {
         )
         .unwrap();
 
-        writeln!(&mut buf, "builddir = {}", self.buildroot.as_str()).unwrap();
         writeln!(
             &mut buf,
             "runner = $builddir/rust/debug/{}",
@@ -26,11 +29,6 @@ impl Build {
         )
         .unwrap();
 
-        for (key, value) in &self.variables {
-            writeln!(&mut buf, "{} = {}", key, value).unwrap();
-        }
-        buf.push('\n');
-
         for (key, value) in &self.pools {
             writeln!(&mut buf, "pool {}\n  depth = {}", key, value).unwrap();
         }
@@ -38,7 +36,7 @@ impl Build {
 
         buf.push_str(&self.output_text);
 
-        for (group, targets) in &self.groups {
+        for (group, targets) in self.groups.iter().sorted() {
             let group = group.replace(':', "_");
             writeln!(
                 &mut buf,
@@ -51,20 +49,22 @@ impl Build {
 
         buf.push_str(&self.trailing_text);
 
+        buf = buf.replace("$builddir", self.buildroot.as_str());
+        for (key, value) in &self.variables {
+            buf = buf.replace(
+                &format!("${key}"),
+                &value.replace("$builddir", self.buildroot.as_str()),
+            );
+        }
+
         buf
     }
 
-    pub fn write_build_file(&self) {
-        let existing_contents = read_to_string("build.ninja").unwrap_or_default();
-        let new_contents = self.render();
-        if existing_contents != new_contents {
-            let folder = &self.buildroot;
-            if !folder.exists() {
-                std::fs::create_dir_all(folder).expect("create build dir");
-            }
-            std::fs::write(folder.join("build.ninja"), new_contents).expect("write build.ninja");
-        }
-
-        // dbg!(&self.groups);
+    pub fn write_build_file(&self) -> Result<()> {
+        create_dir_all(&self.buildroot)?;
+        let path = self.buildroot.join("build.ninja");
+        let contents = self.render().into_bytes();
+        write_file_if_changed(path, contents)?;
+        Ok(())
     }
 }
diff --git a/build/runner/Cargo.toml b/build/runner/Cargo.toml
index e52aeb93f..65dcd975a 100644
--- a/build/runner/Cargo.toml
+++ b/build/runner/Cargo.toml
@@ -16,4 +16,5 @@ clap = { version = "4.2.1", features = ["derive"] }
 itertools = "0.10.5"
 junction = "1.0.0"
 termcolor = "1.2.0"
+which = "4.4.0"
 workspace-hack = { version = "0.1", path = "../../tools/workspace-hack" }
diff --git a/build/runner/src/build.rs b/build/runner/src/build.rs
index 1471dfae6..64afd7f77 100644
--- a/build/runner/src/build.rs
+++ b/build/runner/src/build.rs
@@ -56,7 +56,7 @@ pub fn run_build(args: BuildArgs) {
     let ninja_args = args.args.into_iter().map(|a| a.replace(':', "_"));
 
     let start_time = Instant::now();
-    let mut command = Command::new("ninja");
+    let mut command = Command::new(get_ninja_command());
     command
         .arg("-f")
         .arg(&build_file)
@@ -91,7 +91,12 @@ pub fn run_build(args: BuildArgs) {
         stdout
             .set_color(ColorSpec::new().set_fg(Some(Color::Green)).set_bold(true))
             .unwrap();
-        writeln!(&mut stdout, "\nBuild succeeded.").unwrap();
+        writeln!(
+            &mut stdout,
+            "\nBuild succeeded in {:.2}s.",
+            start_time.elapsed().as_secs_f32()
+        )
+        .unwrap();
         stdout.reset().unwrap();
     } else {
         stdout
@@ -104,6 +109,14 @@ pub fn run_build(args: BuildArgs) {
     }
 }
 
+fn get_ninja_command() -> &'static str {
+    if which::which("n2").is_ok() {
+        "n2"
+    } else {
+        "ninja"
+    }
+}
+
 fn setup_build_root() -> &'static Utf8Path {
     let build_root = Utf8Path::new("out");
 
diff --git a/rslib/i18n/Cargo.toml b/rslib/i18n/Cargo.toml
index eab7c409f..dacb7713a 100644
--- a/rslib/i18n/Cargo.toml
+++ b/rslib/i18n/Cargo.toml
@@ -21,6 +21,8 @@ unic-langid = { version = "0.9.1", features = ["macros"] }
 serde = { version = "1.0.159", features = ["derive"] }
 serde_json = "1.0.95"
 inflections = "1.1.1"
+anki_io = { version = "0.0.0", path = "../io" }
+anyhow = "1.0.71"
 
 [dependencies]
 fluent = "0.16.0"
diff --git a/rslib/i18n/build/main.rs b/rslib/i18n/build/main.rs
index b83b63cad..197cd14da 100644
--- a/rslib/i18n/build/main.rs
+++ b/rslib/i18n/build/main.rs
@@ -6,8 +6,8 @@ mod extract;
 mod gather;
 mod write_strings;
 
-use std::fs;
-
+use anki_io::write_file_if_changed;
+use anyhow::Result;
 use check::check;
 use extract::get_modules;
 use gather::get_ftl_data;
@@ -15,7 +15,7 @@ use write_strings::write_strings;
 
 // fixme: check all variables are present in translations as well?
 
-fn main() {
+fn main() -> Result<()> {
     // generate our own requirements
     let map = get_ftl_data();
     check(&map);
@@ -26,6 +26,7 @@ fn main() {
     println!("cargo:rerun-if-env-changed=STRINGS_JSON");
     if let Some(path) = option_env!("STRINGS_JSON") {
         let meta_json = serde_json::to_string_pretty(&modules).unwrap();
-        fs::write(path, meta_json).unwrap();
+        write_file_if_changed(path, meta_json)?;
     }
+    Ok(())
 }
diff --git a/rslib/io/src/lib.rs b/rslib/io/src/lib.rs
index b4983be84..0c6738872 100644
--- a/rslib/io/src/lib.rs
+++ b/rslib/io/src/lib.rs
@@ -199,6 +199,20 @@ impl Iterator for ReadDirFiles {
     }
 }
 
+pub fn write_file_if_changed(path: impl AsRef<Path>, contents: impl AsRef<[u8]>) -> Result<()> {
+    let path = path.as_ref();
+    let contents = contents.as_ref();
+    let changed = {
+        read_file(path)
+            .map(|existing| existing != contents)
+            .unwrap_or(true)
+    };
+    if changed {
+        write_file(path, contents)?;
+    }
+    Ok(())
+}
+
 #[cfg(test)]
 mod test {
     use super::*;
diff --git a/tools/install-n2 b/tools/install-n2
new file mode 100755
index 000000000..7e47555ef
--- /dev/null
+++ b/tools/install-n2
@@ -0,0 +1,3 @@
+#!/bin/bash
+
+cargo install --git https://github.com/evmar/n2.git --rev e73378d693716715be1a420aa74a2836b49b85c8