diff --git a/examples/Racers offline.yaml b/examples/Racers offline.yaml
new file mode 100644
index 0000000..e5de0f2
--- /dev/null
+++ b/examples/Racers offline.yaml	
@@ -0,0 +1,58 @@
+# Example configuration file for MakeCode Arcade to App to compile to static
+# HTML, CSS, and JS files
+
+# Config version (single number, incremented if breaking change to schema is
+# made)
+version: 1
+
+project:
+  name: Racers
+  path_friendly_name: racers
+  description: "Enjoy the high-speed thrills of car racing in MakeCode Arcade! 
+    For the MakeCode Arcade Mini Game Jam #3."
+  author: Cyrus Yiu
+  version: 1.3.2
+  # This is what the window title will be
+  # This will also be used for the executable file name for Electron outputs
+  # You can use {NAME} or {VERSION} or {AUTHOR} to substitute the correct
+  # values
+  title: "{NAME} v{VERSION}"
+
+inputs:
+  # Can be share_link, github, or path
+  code:
+    type: path
+    value: "E:/Racers"
+
+  assets:
+    # Icon is optional but highly recommended, it will be used as the favicon
+    # and app icon
+    icon:
+      type: path
+      value: "E:/Racers/Racers icon.png"
+
+# Path where the build process will take place
+build_dir: "./examples/Racers-offline-build"
+
+# The MakeCode Arcade version to target
+# Must be explicit 3 number sem ver, do not add a "v" at the beginning
+# To find it, go to https://arcade.makecode.com/ and click on the settings
+# cogwheel button, click About..., and see "arcade version: x.y.z"
+# As of the time of writing this, the latest version is 4.0.14
+target: 2.0.48
+
+# You can have multiple outputs
+# Currently available options are static, static-singlefile, electron, and
+# tauri
+outputs:
+  - type: static
+  - type: static-singlefile
+#  - type: electron
+#    window:
+#      width: 640
+#      height: 480
+#  - type: tauri
+#    identifier: com.unsignedarduino.racers
+#    window:
+#      width: 640
+#      height: 480
diff --git a/examples/Racers.yaml b/examples/Racers.yaml
index 841ee2d..210e28f 100644
--- a/examples/Racers.yaml
+++ b/examples/Racers.yaml
@@ -48,6 +48,13 @@ inputs:
 # Path where the build process will take place
 build_dir: "./examples/Racers-build"
 
+# The MakeCode Arcade version to target
+# Must be explicit 3 number sem ver, do not add a "v" at the beginning
+# To find it, go to https://arcade.makecode.com/ and click on the settings
+# cogwheel button, click About..., and see "arcade version: x.y.z"
+# As of the time of writing this, the latest version is 4.0.14
+target: 4.0.14
+
 # You can have multiple outputs
 # Currently available options are static, static-singlefile, electron, and
 # tauri
diff --git a/pyproject.toml b/pyproject.toml
index eea8454..3783e5d 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -16,6 +16,7 @@ dependencies = [
     "requests",
     "beautifulsoup4",
     "pillow",
+    "platformdirs>=4.11.0",
 ]
 
 [project.scripts]
diff --git a/src/mkcd2app/build_project/__init__.py b/src/mkcd2app/build_project/__init__.py
index 84c0c52..cf0a18c 100644
--- a/src/mkcd2app/build_project/__init__.py
+++ b/src/mkcd2app/build_project/__init__.py
@@ -1,5 +1,4 @@
 import logging
-import shutil
 from contextlib import ExitStack
 from dataclasses import dataclass
 from pathlib import Path
@@ -9,7 +8,7 @@
 
 from mkcd2app.build_project.inputs.code import (
     build_binary_js,
-    download_and_mod_supporting_files,
+    copy_support_files,
     fetch_code,
 )
 from mkcd2app.build_project.website import (
@@ -19,42 +18,13 @@
     install_deps_and_build_website_singlefile,
 )
 from mkcd2app.config import load_config_from_yaml
-from mkcd2app.config.model import StaticOutput, StaticSinglefileOutput
+from mkcd2app.models.config import StaticOutput, StaticSinglefileOutput
 from mkcd2app.utils.logger import create_logger
-from mkcd2app.utils.resources import get_js_tools_path, get_template_path
-from mkcd2app.utils.run import run_cmd
+from mkcd2app.utils.resources import get_resource_template_path
 
 logger = create_logger(name=__name__, level=logging.INFO)
 
 
-@task(namespace="mkcd2app")
-def install_mkcd_build_tools(config_yaml: str, js_tools_src: ContentDir) -> ContentDir:
-    """
-    Installs the MakeCode Arcade build tools.
-
-    :param config_yaml: The raw YAML text of the config file.
-    :param js_tools_src: A redun.ContentDir pointing to the js_tools directory,
-                         so that redun tracks changes to package.json etc.
-    :return: A redun.ContentDir that points to node_modules, this is only used so that
-     redun will see that some tasks depend on `mkc` being installed.
-    """
-    logger.info("Installing MakeCode Arcade build tools")
-
-    config = load_config_from_yaml(config_yaml)
-    build_path = Path(config.build_dir)
-    logger.debug(f"Tools will be installed in {build_path}")
-
-    js_tools_path = Path(js_tools_src.path)
-    shutil.copy(js_tools_path / "package.json", build_path / "package.json")
-    shutil.copy(js_tools_path / "package-lock.json", build_path / "package-lock.json")
-
-    run_cmd(["npm", "ci"], cwd=build_path)
-
-    logger.debug("All MakeCode Arcade build tools installed")
-
-    return ContentDir(str(build_path / "node_modules"))
-
-
 @dataclass
 class BuildProjectResult:
     static: ContentDir | None = None
@@ -79,22 +49,15 @@ def build_project(config_yaml: str) -> BuildProjectResult:
     build_dir.mkdir(parents=True, exist_ok=True)
 
     with ExitStack() as stack:
-        js_tools_path = stack.enter_context(get_js_tools_path())
-        js_tools_content = ContentDir(str(js_tools_path))
-
-        template_path = stack.enter_context(get_template_path("vite-project"))
-        template_content = ContentDir(str(template_path))
+        template_path = stack.enter_context(get_resource_template_path("vite-project"))
+        template_content = ContentDir(str(template_path / "vite-project"))
 
-        # Install `mkc` with `npm ci` in build dir
-        node_modules_for_mkc = install_mkcd_build_tools(config_yaml, js_tools_content)
         # Fetch game source code with `mkc`, `git`, or copy from disk
-        code_path = fetch_code(config_yaml, node_modules_for_mkc)
+        code_path = fetch_code(config_yaml)
         # Build binary.js with `mkc`
         bin_js_path = build_binary_js(config_yaml, code_path)
-        # Download supporting files to run binary.js, including ---simulator.html and all
-        # it's references, and get favicon.ico if present
-        support_path = download_and_mod_supporting_files(config_yaml)
-
+        # Copy ---simulator.html from target dir and get favicon.ico if present
+        support_path = copy_support_files(config_yaml)
         # Copy website template (clean copy with template files only)
         website_path = copy_website_template(config_yaml, template_content)
         # Copy + fill (separate dir so stages don't mutate each other's
@@ -104,7 +67,8 @@ def build_project(config_yaml: str) -> BuildProjectResult:
         )
 
         results = BuildProjectResult()
-
+        # Build the website outputs
+        # Electron and Tauri outputs depend on static_singlefile so redun figures it out
         logger.debug(f"{config.outputs=}")
         for output in config.outputs:
             match output.root:
diff --git a/src/mkcd2app/build_project/inputs/code.py b/src/mkcd2app/build_project/inputs/code.py
index 364cc82..29ac309 100644
--- a/src/mkcd2app/build_project/inputs/code.py
+++ b/src/mkcd2app/build_project/inputs/code.py
@@ -1,31 +1,32 @@
+import json
 import logging
 import shutil
 from io import BytesIO
 from pathlib import Path
 
 import requests
-from bs4 import BeautifulSoup
 from PIL import Image
 from redun import task
 from redun.file import ContentDir, ContentFile
 
 from mkcd2app.config import load_config_from_yaml
-from mkcd2app.config.model import (
+from mkcd2app.models.config import (
     GitHubCodeSource,
     PathAssetSource,
     PathCodeSource,
     ShareLinkCodeSource,
     UrlAssetSource,
 )
+from mkcd2app.utils.filesystem import rmtree_robust
 from mkcd2app.utils.logger import create_logger
-from mkcd2app.utils.paths import rmtree_robust
+from mkcd2app.utils.paths import get_js_tools_bin_dir, get_sim_html_path
 from mkcd2app.utils.run import run_cmd
 
 logger = create_logger(name=__name__, level=logging.INFO)
 
 
 @task(namespace="mkcd2app")
-def fetch_code(config_yaml: str, node_modules_for_mkc: ContentDir) -> ContentDir:
+def fetch_code(config_yaml: str) -> ContentDir:
     """
     Download/clone/copy the source code to the build directory.
 
@@ -33,8 +34,6 @@ def fetch_code(config_yaml: str, node_modules_for_mkc: ContentDir) -> ContentDir
     Example output: ./racers-source
 
     :param config_yaml: The raw YAML text of the config file.
-    :param node_modules_for_mkc: redun.ContentDir that points to the node_modules
-     directory, this ensures that this task depends on `mkc` being installed.
     :return: A redun.ContentDir that points to the source code.
     """
     config = load_config_from_yaml(config_yaml)
@@ -48,10 +47,13 @@ def fetch_code(config_yaml: str, node_modules_for_mkc: ContentDir) -> ContentDir
 
     match config.inputs.code.root:
         case ShareLinkCodeSource(value=url):
-            logger.debug(f"Downloading source code from {url}")
+            logger.debug(f"Downloading source code from {url} with `mkc` CLI")
             code_path.mkdir(parents=True)
-            logger.debug(f"Using `mkc` from {node_modules_for_mkc}")
-            run_cmd(["npx", "mkc", "download", str(url)], cwd=code_path)
+            run_cmd(
+                ["mkc", "download", str(url)],
+                cwd=code_path,
+                which_path=get_js_tools_bin_dir(),
+            )
         case GitHubCodeSource(value=url, checkout=checkout_target):
             logger.debug(f"Cloning source code from {url}@{checkout_target}")
             abs_code_path = code_path.resolve()
@@ -72,6 +74,12 @@ def fetch_code(config_yaml: str, node_modules_for_mkc: ContentDir) -> ContentDir
             logger.debug(f"Copying source code from {path}")
             shutil.copytree(path, code_path)
 
+    mkc_json_path = code_path / "mkc.json"
+    logger.debug("Writing mkc.json")
+    version = config.target
+    mkc_json = {"targetWebsite": f"https://arcade.makecode.com/v{version}"}
+    mkc_json_path.write_text(json.dumps(mkc_json))
+
     logger.debug("Source code downloaded")
     return ContentDir(str(code_path))
 
@@ -94,7 +102,11 @@ def build_binary_js(config_yaml: str, code_path: ContentDir) -> ContentFile:
 
     cwd = Path(code_path.path)
     logger.debug(f"Building in cwd {cwd}")
-    run_cmd(["npx", "mkc", "build", "-j"], cwd=cwd)
+    run_cmd(
+        ["mkc", "build", "-j"],
+        cwd=cwd,
+        which_path=get_js_tools_bin_dir(),
+    )
 
     bin_js_path = cwd / "built" / "binary.js"
     logger.debug(f"binary.js available at {bin_js_path}")
@@ -112,7 +124,7 @@ def build_binary_js(config_yaml: str, code_path: ContentDir) -> ContentFile:
 
 
 @task(namespace="mkcd2app")
-def download_and_mod_supporting_files(config_yaml: str) -> ContentDir:
+def copy_support_files(config_yaml: str) -> ContentDir:
     """
     Download and modify all supporting files needed to run binary.js for the website
 
@@ -128,60 +140,29 @@ def download_and_mod_supporting_files(config_yaml: str) -> ContentDir:
         Path(config.build_dir)
         / f"{config.project.path_friendly_name}-binary-js-support"
     )
-    logger.info(f"Downloading supporting files to {support_path}")
+    target = config.target
+    logger.info(
+        f"Copying ---simulator.html for MakeCode Arcade {target} to {support_path}"
+    )
 
     # Clean previous output, not wasteful because redun handles caching
     if support_path.exists():
         shutil.rmtree(support_path)
     support_path.mkdir(parents=True)
-
-    logger.debug("Downloading main simulator file")
-    res = requests.get("https://trg-arcade.userpxt.io/---simulator")
-    res.raise_for_status()
-    sim_html = res.text
-
-    logger.debug(
-        f"Analyzing sim HTML ({len(sim_html)} chars) for required CSS and JS files"
-    )
-    soup = BeautifulSoup(sim_html, features="html.parser")
-    css_links = soup.find_all("link", rel="stylesheet")
-    js_scripts = soup.find_all("script")
-    logger.debug(f"Found {len(css_links)} CSS links and {len(js_scripts)} JS scripts")
-    for css in css_links:
-        url = css.get("href")
-        if url:
-            logger.debug(f"Downloading CSS file {url}")
-            res = requests.get(str(url))
-            res.raise_for_status()
-            style_tag = soup.new_tag("style")
-            style_tag.string = res.text
-            css.replace_with(style_tag)
-            logger.debug(f"Inlined CSS from {url}")
-    for js in js_scripts:
-        url = js.get("src")
-        if url:
-            logger.debug(f"Downloading JS file {url}")
-            res = requests.get(str(url))
-            res.raise_for_status()
-            js.string = res.text
-            del js["src"]
-            logger.debug(f"Inlined JS from {url}")
-    new_sim_html = soup.prettify(formatter="html5")
-    path = support_path / "---simulator.html"
-    path.write_text(new_sim_html)
-    logger.debug(f"Wrote modified simulator HTML to {path}")
+    # Only one file to copy
+    shutil.copy(get_sim_html_path(target), support_path)
 
     if config.inputs.assets.icon:
         match config.inputs.assets.icon.root:
-            case UrlAssetSource(value=url):  # type: ignore[misc]
-                logger.debug(f"Downloading icon from {url}")
-                res = requests.get(str(url))
+            case UrlAssetSource(value=icon_url):
+                logger.debug(f"Downloading icon from {icon_url}")
+                res = requests.get(str(icon_url))
                 res.raise_for_status()
                 buffer = BytesIO(res.content)
                 im = Image.open(buffer)
-            case PathAssetSource(value=path):  # type: ignore[misc]
-                logger.debug(f"Opening icon from {path}")
-                im = Image.open(path)
+            case PathAssetSource(value=icon_path):
+                logger.debug(f"Opening icon from {icon_path}")
+                im = Image.open(icon_path)
         favicon_path = support_path / "favicon.ico"
         logger.debug(f"Saving favicon to {favicon_path}")
         im.save(favicon_path)
diff --git a/src/mkcd2app/build_project/website.py b/src/mkcd2app/build_project/website.py
index 126865c..98d4055 100644
--- a/src/mkcd2app/build_project/website.py
+++ b/src/mkcd2app/build_project/website.py
@@ -9,6 +9,7 @@
 
 from mkcd2app.config import load_config_from_yaml
 from mkcd2app.utils.logger import create_logger
+from mkcd2app.utils.paths import get_templates_npm_cache_dir
 from mkcd2app.utils.run import run_cmd
 
 logger = create_logger(name=__name__, level=logging.INFO)
@@ -143,7 +144,10 @@ def install_deps_and_build_website(website_filled_path: ContentDir) -> ContentDi
         shutil.rmtree(dst)
     shutil.copytree(src, dst)
 
-    run_cmd(["npm", "ci"], cwd=dst)
+    cache_path = get_templates_npm_cache_dir()
+    logger.debug(f"Using template npm cache at {cache_path} to install")
+
+    run_cmd(["npm", "ci", "--cache", str(cache_path), "--offline"], cwd=dst)
     logger.debug("Website dependencies installed")
 
     run_cmd(["npm", "run", "build"], cwd=dst)
@@ -180,7 +184,10 @@ def install_deps_and_build_website_singlefile(
         shutil.rmtree(dst)
     shutil.copytree(src, dst)
 
-    run_cmd(["npm", "ci"], cwd=dst)
+    cache_path = get_templates_npm_cache_dir()
+    logger.debug(f"Using template npm cache at {cache_path} to install")
+
+    run_cmd(["npm", "ci", "--cache", str(cache_path), "--offline"], cwd=dst)
     logger.debug("Website dependencies installed")
 
     run_cmd(["npm", "run", "build:singlefile"], cwd=dst)
diff --git a/src/mkcd2app/cli.py b/src/mkcd2app/cli.py
index 4ea7402..20a9cd0 100644
--- a/src/mkcd2app/cli.py
+++ b/src/mkcd2app/cli.py
@@ -13,16 +13,17 @@ def generate_and_parse_args() -> Namespace:
     :return: A `Namespace` object with parsed CLI arguments.
     """
     parser = ArgumentParser(
+        prog="mkcd2app",
         description="Convert your MakeCode Arcade games into a "
-        "standalone offline executable!"
+        "standalone offline executable!",
     )
     parser.add_argument(
         "--debug",
         action="store_true",
-        help="Enable debug logging. This must go first before the sub command.",
+        help="Enable debug logging. This must go first before any sub commands.",
     )
     subparsers = parser.add_subparsers(required=True, dest="command")
-    # build subcommand
+
     parser_build = subparsers.add_parser(
         "build", help="Build your MakeCode Arcade game."
     )
@@ -33,6 +34,46 @@ def generate_and_parse_args() -> Namespace:
         help="Delete the entire build directory before building.",
     )
 
+    parser_toolchain = subparsers.add_parser(
+        "toolchain", help="Manage the MakeCode CLI toolchain."
+    )
+    toolchain_subparsers = parser_toolchain.add_subparsers(
+        required=True, dest="toolchain_command"
+    )
+    toolchain_subparsers.add_parser(
+        "install",
+        help="Install the MakeCode CLI toolchain for this specific mkcd2app version.",
+    )
+    toolchain_subparsers.add_parser(
+        "status", help="Show the installed MakeCode CLI toolchain."
+    )
+    toolchain_subparsers.add_parser(
+        "uninstall",
+        help="Uninstall the MakeCode CLI toolchain for this specific mkcd2app version.",
+    )
+
+    parser_target = subparsers.add_parser(
+        "target", help="Manage MakeCode Arcade target versions."
+    )
+    target_subparsers = parser_target.add_subparsers(
+        required=True, dest="target_command"
+    )
+    parser_target_install = target_subparsers.add_parser(
+        "install", help="Install a MakeCode Arcade target version."
+    )
+    parser_target_install.add_argument(
+        "version", type=str, help="Target version to install."
+    )
+    target_subparsers.add_parser(
+        "list", help="List installed MakeCode Arcade target versions."
+    )
+    parser_target_uninstall = target_subparsers.add_parser(
+        "uninstall", help="Uninstall a MakeCode Arcade target version."
+    )
+    parser_target_uninstall.add_argument(
+        "version", type=str, help="Target version to uninstall."
+    )
+
     args = parser.parse_args()
     logger.debug(f"Received arguments: {args}")
     return args
diff --git a/src/mkcd2app/config/__init__.py b/src/mkcd2app/config/__init__.py
index 8f1d4c4..d5cbc40 100644
--- a/src/mkcd2app/config/__init__.py
+++ b/src/mkcd2app/config/__init__.py
@@ -2,7 +2,7 @@
 
 import yaml
 
-from mkcd2app.config.model import BuildConfig
+from mkcd2app.models.config import BuildConfig
 from mkcd2app.utils.logger import create_logger
 
 logger = create_logger(name=__name__, level=logging.INFO)
diff --git a/src/mkcd2app/main.py b/src/mkcd2app/main.py
index ef7bbd2..524c508 100644
--- a/src/mkcd2app/main.py
+++ b/src/mkcd2app/main.py
@@ -2,14 +2,20 @@
 import shutil
 from pathlib import Path
 
-import redun
-import redun.file
-from redun import Scheduler
-
 from mkcd2app.build_project import BuildProjectResult, build_project
 from mkcd2app.cli import generate_and_parse_args
 from mkcd2app.config import load_config_from_yaml
+from mkcd2app.target.install import install_target
+from mkcd2app.target.uninstall import uninstall_target
+from mkcd2app.toolchain.install import install_toolchain
+from mkcd2app.toolchain.uninstall import uninstall_toolchain
 from mkcd2app.utils.logger import create_logger, set_all_stdout_logger_levels
+from mkcd2app.utils.paths import (
+    get_redun_db_for_target_path,
+    get_redun_db_for_toolchain_path,
+)
+from mkcd2app.utils.run_redun_task import run_redun_task
+from mkcd2app.utils.text import raise_for_invalid_strict_semver
 
 logger = create_logger(name=__name__, level=logging.INFO)
 
@@ -21,11 +27,55 @@ def main() -> None:
         set_all_stdout_logger_levels(logging.DEBUG)
     logger.debug(f"Received arguments: {args}")
 
-    if args.command == "build":
-        logger.debug("Building project")
+    if args.command == "toolchain":
+        if args.toolchain_command == "install":
+            logger.debug("Installing MakeCode CLI toolchain")
+            run_redun_task(
+                expr=install_toolchain(),
+                redun_db_path=get_redun_db_for_toolchain_path(),
+            )
+            logger.debug("Toolchain installed")
+        elif args.toolchain_command == "status":
+            logger.debug("Checking MakeCode CLI toolchain status")
+
+        elif args.toolchain_command == "uninstall":
+            logger.debug("Uninstalling MakeCode CLI toolchain")
+            # noinspection none-function-assignment
+            run_redun_task(
+                expr=uninstall_toolchain(),
+                redun_db_path=get_redun_db_for_toolchain_path(),
+            )
+            logger.debug("Toolchain uninstalled")
+    elif args.command == "target":
+        if args.target_command == "install":
+            install_version: str = args.version
+            raise_for_invalid_strict_semver(install_version)
+            logger.debug(f"Installing MakeCode CLI target version {install_version}")
+            run_redun_task(
+                expr=install_target(install_version),
+                redun_db_path=get_redun_db_for_target_path(),
+            )
+            logger.debug(f"Target {install_version} installed")
+        elif args.target_command == "list":
+            logger.debug("Listing MakeCode CLI target")
 
+        elif args.target_command == "uninstall":
+            uninstall_version: str = args.version
+            raise_for_invalid_strict_semver(uninstall_version)
+            logger.debug(
+                f"Uninstalling MakeCode CLI target version {uninstall_version}"
+            )
+            # noinspection none-function-assignment
+            run_redun_task(
+                expr=uninstall_target(uninstall_version),
+                redun_db_path=get_redun_db_for_target_path(),
+            )
+            logger.debug(f"Target {uninstall_version} uninstalled")
+
+    elif args.command == "build":
         config_path = Path(args.config)
-        logger.debug(f"Loading config from {config_path}")
+        logger.debug(f"Building project with config {config_path}")
+
         config_text = config_path.read_text()
 
         # Parse once only to extract build_dir for the redun DB path.
@@ -42,24 +92,10 @@ def main() -> None:
             else:
                 logger.debug("Build directory does not exist; nothing to clear")
 
-        build_dir.mkdir(parents=True, exist_ok=True)
-        db_uri = f"sqlite:///{build_dir.resolve() / '.redun-cache.db'}"
-        logger.debug(f"redun cache DB: {db_uri}")
-        # noinspection PyUnresolvedReferences
-        redun_config = redun.config.Config(
-            {
-                "scheduler": {"log_level": "DEBUG"},
-                "backend": {"db_uri": db_uri},
-            }
-        )
-        scheduler = Scheduler(config=redun_config)
-        # Load/migrate the backend so the persistent DB is properly set up.
-        # Without this, providing a custom db_uri skips the automatic
-        # engine creation and migration that the in-memory default does.
-        scheduler.load()
-        results: BuildProjectResult = scheduler.run(
-            build_project(config_text),
+        results: BuildProjectResult = run_redun_task(
+            build_project(config_text), build_dir.resolve() / ".redun-cache.db"
         )
+
         if results.static:
             logger.info(f"Static website directory is at {results.static.path}")
         if results.static_singlefile:
diff --git a/src/mkcd2app/models/__init__.py b/src/mkcd2app/models/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/src/mkcd2app/config/model.py b/src/mkcd2app/models/config.py
similarity index 98%
rename from src/mkcd2app/config/model.py
rename to src/mkcd2app/models/config.py
index 6e13453..d08a245 100644
--- a/src/mkcd2app/config/model.py
+++ b/src/mkcd2app/models/config.py
@@ -109,6 +109,7 @@ class BuildConfig(BaseModel):
     project: Project
     inputs: Inputs
     build_dir: str = Field(..., alias="build_dir")
+    target: str = Field(..., alias="target")
     outputs: list[OutputOption]
 
     class Config:
diff --git a/src/mkcd2app/models/metadata.py b/src/mkcd2app/models/metadata.py
new file mode 100644
index 0000000..85c4d97
--- /dev/null
+++ b/src/mkcd2app/models/metadata.py
@@ -0,0 +1,19 @@
+from pydantic import BaseModel, Field, HttpUrl
+
+
+# {
+#   "simUrl":"https://trg-arcade.userpxt.io/---simulator",
+#   "cdnUrl":"https://cdn.makecode.com",
+#   "version":"v0.0.0",
+#   "target":"arcade",
+#   "targetVersion":"4.0.14"
+# }
+class BinaryJSMetadata(BaseModel):
+    simUrl: HttpUrl = Field(..., description="Simulator URL")
+    cdnUrl: HttpUrl = Field(..., description="CDN base URL")
+    version: str = Field(..., description="Package version")
+    target: str = Field(..., description="Build target name")
+    targetVersion: str = Field(..., description="Target version string")
+
+    class Config:
+        extra = "forbid"
diff --git a/src/mkcd2app/resources/empty_project/README.md b/src/mkcd2app/resources/empty_project/README.md
new file mode 100644
index 0000000..0519ecb
--- /dev/null
+++ b/src/mkcd2app/resources/empty_project/README.md
@@ -0,0 +1 @@
+ 
\ No newline at end of file
diff --git a/src/mkcd2app/resources/empty_project/assets.json b/src/mkcd2app/resources/empty_project/assets.json
new file mode 100644
index 0000000..e69de29
diff --git a/src/mkcd2app/resources/empty_project/main.ts b/src/mkcd2app/resources/empty_project/main.ts
new file mode 100644
index 0000000..8b13789
--- /dev/null
+++ b/src/mkcd2app/resources/empty_project/main.ts
@@ -0,0 +1 @@
+
diff --git a/src/mkcd2app/resources/empty_project/pxt.json b/src/mkcd2app/resources/empty_project/pxt.json
new file mode 100644
index 0000000..782e85f
--- /dev/null
+++ b/src/mkcd2app/resources/empty_project/pxt.json
@@ -0,0 +1,12 @@
+{
+  "name": "empty_project",
+  "description": "",
+  "dependencies": {
+    "device": "*"
+  },
+  "files": [
+    "main.ts",
+    "README.md",
+    "assets.json"
+  ]
+}
diff --git a/src/mkcd2app/js_tools/package-lock.json b/src/mkcd2app/resources/js_tools/package-lock.json
similarity index 100%
rename from src/mkcd2app/js_tools/package-lock.json
rename to src/mkcd2app/resources/js_tools/package-lock.json
diff --git a/src/mkcd2app/js_tools/package.json b/src/mkcd2app/resources/js_tools/package.json
similarity index 100%
rename from src/mkcd2app/js_tools/package.json
rename to src/mkcd2app/resources/js_tools/package.json
diff --git a/src/mkcd2app/templates/vite-project/.gitignore b/src/mkcd2app/resources/templates/vite-project/.gitignore
similarity index 100%
rename from src/mkcd2app/templates/vite-project/.gitignore
rename to src/mkcd2app/resources/templates/vite-project/.gitignore
diff --git a/src/mkcd2app/templates/vite-project/.prettierignore b/src/mkcd2app/resources/templates/vite-project/.prettierignore
similarity index 100%
rename from src/mkcd2app/templates/vite-project/.prettierignore
rename to src/mkcd2app/resources/templates/vite-project/.prettierignore
diff --git a/src/mkcd2app/templates/vite-project/README.md b/src/mkcd2app/resources/templates/vite-project/README.md
similarity index 100%
rename from src/mkcd2app/templates/vite-project/README.md
rename to src/mkcd2app/resources/templates/vite-project/README.md
diff --git a/src/mkcd2app/templates/vite-project/eslint.config.js b/src/mkcd2app/resources/templates/vite-project/eslint.config.js
similarity index 100%
rename from src/mkcd2app/templates/vite-project/eslint.config.js
rename to src/mkcd2app/resources/templates/vite-project/eslint.config.js
diff --git a/src/mkcd2app/templates/vite-project/index.html b/src/mkcd2app/resources/templates/vite-project/index.html
similarity index 100%
rename from src/mkcd2app/templates/vite-project/index.html
rename to src/mkcd2app/resources/templates/vite-project/index.html
diff --git a/src/mkcd2app/templates/vite-project/package-lock.json b/src/mkcd2app/resources/templates/vite-project/package-lock.json
similarity index 100%
rename from src/mkcd2app/templates/vite-project/package-lock.json
rename to src/mkcd2app/resources/templates/vite-project/package-lock.json
diff --git a/src/mkcd2app/templates/vite-project/package.json b/src/mkcd2app/resources/templates/vite-project/package.json
similarity index 93%
rename from src/mkcd2app/templates/vite-project/package.json
rename to src/mkcd2app/resources/templates/vite-project/package.json
index 63636b0..47898f3 100644
--- a/src/mkcd2app/templates/vite-project/package.json
+++ b/src/mkcd2app/resources/templates/vite-project/package.json
@@ -7,8 +7,8 @@
     "dev": "vite",
     "lint": "eslint ",
     "writeLint": "eslint --fix ",
-    "format": "prettier --check .",
-    "writeFormat": "prettier --write .",
+    "format": "prettier --check ",
+    "writeFormat": "prettier --write ",
     "preview": "vite preview",
     "build": "tsc -b && vite build",
     "build:singlefile": "tsc -b && vite build --mode singlefile"
diff --git a/src/mkcd2app/templates/vite-project/src/App.css b/src/mkcd2app/resources/templates/vite-project/src/App.css
similarity index 100%
rename from src/mkcd2app/templates/vite-project/src/App.css
rename to src/mkcd2app/resources/templates/vite-project/src/App.css
diff --git a/src/mkcd2app/templates/vite-project/src/App.tsx b/src/mkcd2app/resources/templates/vite-project/src/App.tsx
similarity index 100%
rename from src/mkcd2app/templates/vite-project/src/App.tsx
rename to src/mkcd2app/resources/templates/vite-project/src/App.tsx
diff --git a/src/mkcd2app/templates/vite-project/src/assets/---simulator.html b/src/mkcd2app/resources/templates/vite-project/src/assets/---simulator.html
similarity index 100%
rename from src/mkcd2app/templates/vite-project/src/assets/---simulator.html
rename to src/mkcd2app/resources/templates/vite-project/src/assets/---simulator.html
diff --git a/src/mkcd2app/templates/vite-project/src/assets/binary.js b/src/mkcd2app/resources/templates/vite-project/src/assets/binary.js
similarity index 100%
rename from src/mkcd2app/templates/vite-project/src/assets/binary.js
rename to src/mkcd2app/resources/templates/vite-project/src/assets/binary.js
diff --git a/src/mkcd2app/templates/vite-project/src/gameConfiguration.ts b/src/mkcd2app/resources/templates/vite-project/src/gameConfiguration.ts
similarity index 100%
rename from src/mkcd2app/templates/vite-project/src/gameConfiguration.ts
rename to src/mkcd2app/resources/templates/vite-project/src/gameConfiguration.ts
diff --git a/src/mkcd2app/templates/vite-project/src/global.d.ts b/src/mkcd2app/resources/templates/vite-project/src/global.d.ts
similarity index 100%
rename from src/mkcd2app/templates/vite-project/src/global.d.ts
rename to src/mkcd2app/resources/templates/vite-project/src/global.d.ts
diff --git a/src/mkcd2app/templates/vite-project/src/main.tsx b/src/mkcd2app/resources/templates/vite-project/src/main.tsx
similarity index 100%
rename from src/mkcd2app/templates/vite-project/src/main.tsx
rename to src/mkcd2app/resources/templates/vite-project/src/main.tsx
diff --git a/src/mkcd2app/templates/vite-project/src/utils/position.ts b/src/mkcd2app/resources/templates/vite-project/src/utils/position.ts
similarity index 100%
rename from src/mkcd2app/templates/vite-project/src/utils/position.ts
rename to src/mkcd2app/resources/templates/vite-project/src/utils/position.ts
diff --git a/src/mkcd2app/templates/vite-project/src/utils/toasts.ts b/src/mkcd2app/resources/templates/vite-project/src/utils/toasts.ts
similarity index 100%
rename from src/mkcd2app/templates/vite-project/src/utils/toasts.ts
rename to src/mkcd2app/resources/templates/vite-project/src/utils/toasts.ts
diff --git a/src/mkcd2app/templates/vite-project/tsconfig.app.json b/src/mkcd2app/resources/templates/vite-project/tsconfig.app.json
similarity index 85%
rename from src/mkcd2app/templates/vite-project/tsconfig.app.json
rename to src/mkcd2app/resources/templates/vite-project/tsconfig.app.json
index e30ef7d..3abe7e5 100644
--- a/src/mkcd2app/templates/vite-project/tsconfig.app.json
+++ b/src/mkcd2app/resources/templates/vite-project/tsconfig.app.json
@@ -2,9 +2,14 @@
   "compilerOptions": {
     "tsBuildInfoFile": "./node_modules/.tmp/tsconfig.app.tsbuildinfo",
     "target": "es2023",
-    "lib": ["ES2023", "DOM"],
+    "lib": [
+      "ES2023",
+      "DOM"
+    ],
     "module": "esnext",
-    "types": ["vite/client"],
+    "types": [
+      "vite/client"
+    ],
     "allowArbitraryExtensions": true,
     "skipLibCheck": true,
     /* Bundler mode */
@@ -20,5 +25,7 @@
     "erasableSyntaxOnly": false,
     "noFallthroughCasesInSwitch": true
   },
-  "include": ["src"]
+  "include": [
+    "src"
+  ]
 }
diff --git a/src/mkcd2app/templates/vite-project/tsconfig.json b/src/mkcd2app/resources/templates/vite-project/tsconfig.json
similarity index 100%
rename from src/mkcd2app/templates/vite-project/tsconfig.json
rename to src/mkcd2app/resources/templates/vite-project/tsconfig.json
diff --git a/src/mkcd2app/templates/vite-project/tsconfig.node.json b/src/mkcd2app/resources/templates/vite-project/tsconfig.node.json
similarity index 81%
rename from src/mkcd2app/templates/vite-project/tsconfig.node.json
rename to src/mkcd2app/resources/templates/vite-project/tsconfig.node.json
index 1f8a29b..3bf20da 100644
--- a/src/mkcd2app/templates/vite-project/tsconfig.node.json
+++ b/src/mkcd2app/resources/templates/vite-project/tsconfig.node.json
@@ -2,8 +2,12 @@
   "compilerOptions": {
     "tsBuildInfoFile": "./node_modules/.tmp/tsconfig.node.tsbuildinfo",
     "target": "es2023",
-    "lib": ["ES2023"],
-    "types": ["node"],
+    "lib": [
+      "ES2023"
+    ],
+    "types": [
+      "node"
+    ],
     "skipLibCheck": true,
     /* Bundler mode */
     "module": "nodenext",
@@ -17,5 +21,7 @@
     "erasableSyntaxOnly": true,
     "noFallthroughCasesInSwitch": true
   },
-  "include": ["vite.config.ts"]
+  "include": [
+    "vite.config.ts"
+  ]
 }
diff --git a/src/mkcd2app/templates/vite-project/vite.config.ts b/src/mkcd2app/resources/templates/vite-project/vite.config.ts
similarity index 100%
rename from src/mkcd2app/templates/vite-project/vite.config.ts
rename to src/mkcd2app/resources/templates/vite-project/vite.config.ts
diff --git a/src/mkcd2app/target/__init__.py b/src/mkcd2app/target/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/src/mkcd2app/target/install.py b/src/mkcd2app/target/install.py
new file mode 100644
index 0000000..df40b40
--- /dev/null
+++ b/src/mkcd2app/target/install.py
@@ -0,0 +1,148 @@
+import json
+import logging
+import shutil
+from contextlib import ExitStack
+from pathlib import Path
+from tempfile import TemporaryDirectory
+
+import requests
+from bs4 import BeautifulSoup
+from redun import task
+from redun.file import ContentDir, ContentFile
+
+from mkcd2app.models.metadata import BinaryJSMetadata
+from mkcd2app.utils.logger import create_logger
+from mkcd2app.utils.paths import (
+    get_js_tools_bin_dir,
+    get_sim_html_path,
+)
+from mkcd2app.utils.resources import get_resource_empty_project_path
+from mkcd2app.utils.run import run_cmd
+from mkcd2app.utils.text import extract_meta_comment
+
+logger = create_logger(name=__name__, level=logging.INFO)
+
+
+@task(namespace="mkcd2app")
+def warm_mkc_cache_for_version_and_get_binary_js_metadata(
+    empty_prj: ContentDir, version: str
+) -> str:
+    """
+    Warm the mkc compiler cache by building an empty project for the target MakeCode
+    Arcade version in a temporary directory.
+
+    :param empty_prj: The ContentDir pointing to the directory containing the empty
+     MakeCode Arcade project.
+    :param version: The MakeCode Arcade version to target. E.g., "4.0.14". Must be
+     explicit 3 num sem ver, not just like "4.0" or "4", and do not include a "v".
+    :return: A BinaryJSMetadata model dumped to a JSON string.
+    """
+    logger.info(f"Warming mkc compiler cache for MakeCode Arcade version {version}")
+
+    empty_prj_path = Path(empty_prj.path)
+
+    with TemporaryDirectory() as tmp_dir:
+        tmp_dir_path = Path(tmp_dir)
+
+        logger.debug(f"Copying {empty_prj_path} to {tmp_dir_path}")
+        shutil.copytree(empty_prj_path, tmp_dir_path, dirs_exist_ok=True)
+
+        mkc_json_path = tmp_dir_path / "mkc.json"
+        logger.debug("Writing mkc.json")
+        mkc_json = {"targetWebsite": f"https://arcade.makecode.com/v{version}"}
+        mkc_json_path.write_text(json.dumps(mkc_json))
+
+        logger.debug("Running build to warm cache")
+        run_cmd(
+            ["mkc", "build", "-j"], cwd=tmp_dir_path, which_path=get_js_tools_bin_dir()
+        )
+
+        binary_js_path = tmp_dir_path / "built" / "binary.js"
+        logger.debug(f"binary.js available at {binary_js_path}")
+
+        logger.debug("Finished mkc cache warming, extracting binary.js metadata")
+        metadata = extract_meta_comment(binary_js_path)
+        logger.debug(f"{metadata=}")
+        return metadata.model_dump_json()
+
+
+@task(namespace="mkcd2app")
+def download_sim(bin_js_metadata: str, version: str) -> ContentFile:
+    """
+    Download the simulator HTML and the supporting files needed to run binary.js for the
+    website.
+
+    :param bin_js_metadata: The binary JS metadata JSON as a string.
+    :param version: The MakeCode Arcade version to target. E.g., "4.0.14". Must be
+     explicit 3 num sem ver, not just like "4.0" or "4", and do not include a "v".
+    :return: A ContentFile that points to the ---simulator.html.
+    """
+    metadata = BinaryJSMetadata.model_validate_json(bin_js_metadata)
+    logger.info(
+        f"Downloading simulator for MakeCode Arcade version {metadata.targetVersion}"
+    )
+
+    logger.debug(f"Downloading main simulator file from {metadata.simUrl}")
+    res = requests.get(str(metadata.simUrl))
+    res.raise_for_status()
+    sim_html = res.text
+
+    logger.debug(
+        f"Analyzing sim HTML ({len(sim_html)} chars) for required CSS and JS files"
+    )
+    soup = BeautifulSoup(sim_html, features="html.parser")
+    css_links = soup.find_all("link", rel="stylesheet")
+    js_scripts = soup.find_all("script")
+    logger.debug(f"Found {len(css_links)} CSS links and {len(js_scripts)} JS scripts")
+    for css in css_links:
+        url = css.get("href")
+        if url:
+            logger.debug(f"Downloading CSS file {url}")
+            res = requests.get(str(url))
+            res.raise_for_status()
+            style_tag = soup.new_tag("style")
+            style_tag.string = res.text
+            css.replace_with(style_tag)
+            logger.debug(f"Inlined CSS from {url}")
+    for js in js_scripts:
+        url = js.get("src")
+        if url:
+            logger.debug(f"Downloading JS file {url}")
+            res = requests.get(str(url))
+            res.raise_for_status()
+            js.string = res.text
+            del js["src"]
+            logger.debug(f"Inlined JS from {url}")
+    new_sim_html = soup.prettify(formatter="html5")
+
+    path = get_sim_html_path(version)
+    path.parent.mkdir(parents=True, exist_ok=True)
+    path.write_text(new_sim_html)
+
+    logger.debug(f"Wrote simulator HTML to {path}")
+
+    return ContentFile(str(path))
+
+
+@task(namespace="mkcd2app")
+def install_target(version: str) -> ContentFile:
+    """
+    Install a MakeCode Arcade target version for this mkcd2app version.
+
+    :param version: The MakeCode Arcade version to target. E.g., "4.0.14". Must be
+     explicit 3 num sem ver, not just like "4.0" or "4", and do not include a "v".
+    :return: A ContentFile that points to the ---simulator.html for the installed version.
+    """
+    logger.info(f"Installing MakeCode Arcade target version {version}")
+
+    with ExitStack() as stack:
+        empty_prj_path = stack.enter_context(get_resource_empty_project_path())
+
+        # `mkc build -j` an empty project with the correct version
+        metadata = warm_mkc_cache_for_version_and_get_binary_js_metadata(
+            ContentDir(str(empty_prj_path)), version
+        )
+        # Download ---simulator.html and supporting files, mod into single HTML file
+        sim_html = download_sim(metadata, version)
+
+        return sim_html
diff --git a/src/mkcd2app/target/uninstall.py b/src/mkcd2app/target/uninstall.py
new file mode 100644
index 0000000..80c461c
--- /dev/null
+++ b/src/mkcd2app/target/uninstall.py
@@ -0,0 +1,24 @@
+import logging
+
+from redun import task
+
+from mkcd2app.utils.filesystem import rmtree_robust
+from mkcd2app.utils.logger import create_logger
+from mkcd2app.utils.paths import get_target_version_dir
+
+logger = create_logger(name=__name__, level=logging.INFO)
+
+
+@task(namespace="mkcd2app")
+def uninstall_target(version: str) -> None:
+    """
+    Uninstall a MakeCode Arcade target version for this mkcd2app version.
+
+    :param version: The MakeCode Arcade version to target. E.g., "4.0.14". Must be
+     explicit 3 num sem ver, not just like "4.0" or "4", and do not include a "v".
+    """
+    logger.info(f"Uninstall MakeCode Arcade target version {version}")
+
+    target_path = get_target_version_dir(version)
+    logger.debug(f"Removing target directory {target_path}")
+    rmtree_robust(target_path)
diff --git a/src/mkcd2app/toolchain/__init__.py b/src/mkcd2app/toolchain/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/src/mkcd2app/toolchain/install.py b/src/mkcd2app/toolchain/install.py
new file mode 100644
index 0000000..b8b32b3
--- /dev/null
+++ b/src/mkcd2app/toolchain/install.py
@@ -0,0 +1,110 @@
+import logging
+import shutil
+from contextlib import ExitStack
+from pathlib import Path
+from tempfile import TemporaryDirectory
+
+from redun import task
+from redun.file import ContentDir
+
+from mkcd2app.utils.logger import create_logger
+from mkcd2app.utils.paths import (
+    get_js_tools_dir,
+    get_templates_npm_cache_dir,
+)
+from mkcd2app.utils.resources import (
+    get_resource_js_tools_path,
+    get_resource_template_path,
+)
+from mkcd2app.utils.run import run_cmd
+
+logger = create_logger(name=__name__, level=logging.INFO)
+
+
+@task(namespace="mkcd2app")
+def install_js_tools(js_tools: ContentDir) -> ContentDir:
+    """
+    Installs necessary JS tools for mkcd2app.
+
+    :param js_tools: The ContentDir pointing to the directory containing the
+     package.json and package-lock.json, which include the tools to install.
+    :return: A ContentDir pointing to node_modules, to ensure redun sees that this task
+     has something that depends on its results.
+    """
+    logger.info("Installing JS tools")
+
+    source_path = Path(js_tools.path)
+    dest_path = get_js_tools_dir()
+    dest_path.mkdir(parents=True, exist_ok=True)
+
+    logger.debug(f"Copying package files from {source_path} to {dest_path}")
+    shutil.copy(source_path / "package.json", dest_path / "package.json")
+    shutil.copy(source_path / "package-lock.json", dest_path / "package-lock.json")
+
+    logger.debug("`npm ci` to download")
+    run_cmd(["npm", "ci"], cwd=dest_path)
+
+    logger.debug("All JS tools installed")
+    return ContentDir(str(dest_path / "node_modules"))
+
+
+@task(namespace="mkcd2app")
+def warm_npm_cache_for_templates(templates: ContentDir) -> ContentDir:
+    """
+    For every template in the templates directory, copy them to a temporary directory,
+    run `npm ci --cache CACHE_DIR --prefer-online` where CACHE_DIR
+
+    :param templates: The ContentDir pointing to the directory containing the templates.
+    :return: A ContentDir pointing to node_modules, to ensure redun sees that this task
+     has something that depends on its results.
+    """
+    logger.info("Warming npm cache for templates")
+
+    source_path = Path(templates.path)
+    cache_path = get_templates_npm_cache_dir()
+    cache_path.mkdir(parents=True, exist_ok=True)
+
+    logger.debug(f"Looking for templates in {source_path}")
+
+    all_templates = list(source_path.iterdir())
+    logger.debug(f"Found {len(all_templates)} templates")
+
+    for template in all_templates:
+        logger.debug(f"Caching packages for template {template.name}")
+        with TemporaryDirectory() as tmp_dir:
+            tmp_dir_path = Path(tmp_dir)
+            logger.debug(f"Copying {template} to {tmp_dir_path}")
+            shutil.copytree(template, tmp_dir_path, dirs_exist_ok=True)
+
+            logger.debug("Caching npm packages")
+            run_cmd(
+                ["npm", "ci", "--cache", str(cache_path), "--prefer-online"],
+                cwd=tmp_dir_path,
+            )
+
+    logger.debug(f"npm cache filled at {cache_path}")
+    return ContentDir(str(cache_path))
+
+
+@task(namespace="mkcd2app")
+def install_toolchain() -> tuple[ContentDir, ContentDir]:
+    """
+    Install the toolchain for this mkcd2app version.
+
+    :return: A tuple of two ContentDirs, where the first one is the node_modules folder
+     for the JS tools, and the other one is the cache directory for the templates.
+    """
+    logger.info("Installing toolchain")
+
+    with ExitStack() as stack:
+        js_tools_path = stack.enter_context(get_resource_js_tools_path())
+        templates_path = stack.enter_context(get_resource_template_path())
+
+        # `npm ci` the necessary tools (`mkc` CLI itself)
+        js_tools_node_modules = install_js_tools(ContentDir(str(js_tools_path)))
+        # `npm ci --cache CACHE_DIR --prefer-online` for all templates
+        templates_npm_cache = warm_npm_cache_for_templates(
+            ContentDir(str(templates_path))
+        )
+
+        return js_tools_node_modules, templates_npm_cache
diff --git a/src/mkcd2app/toolchain/uninstall.py b/src/mkcd2app/toolchain/uninstall.py
new file mode 100644
index 0000000..af77558
--- /dev/null
+++ b/src/mkcd2app/toolchain/uninstall.py
@@ -0,0 +1,22 @@
+import logging
+
+from redun import task
+
+from mkcd2app.utils.filesystem import rmtree_robust
+from mkcd2app.utils.logger import create_logger
+from mkcd2app.utils.paths import get_toolchain_dir
+
+logger = create_logger(name=__name__, level=logging.INFO)
+
+
+@task(namespace="mkcd2app")
+def uninstall_toolchain() -> None:
+    """
+    Uninstall the toolchain for this mkcd2app version by removing the toolchain
+    directory and its redun cache DB.
+    """
+    logger.info("Uninstalling toolchain")
+
+    toolchain_path = get_toolchain_dir()
+    logger.debug(f"Removing toolchain directory {toolchain_path}")
+    rmtree_robust(toolchain_path)
diff --git a/src/mkcd2app/utils/filesystem.py b/src/mkcd2app/utils/filesystem.py
new file mode 100644
index 0000000..5a9d0b8
--- /dev/null
+++ b/src/mkcd2app/utils/filesystem.py
@@ -0,0 +1,25 @@
+import os
+import shutil
+import stat
+from pathlib import Path
+from types import TracebackType
+from typing import Any
+
+
+def _remove_readonly(
+    func: Any,
+    path: str,
+    exc_info: tuple[type[BaseException], BaseException, TracebackType],
+) -> None:
+    """shutil.rmtree error handler: clear read-only bit and retry.
+
+    Needed on Windows because git marks files under .git/objects (and
+    sometimes .git itself) read-only, which makes os.unlink/os.rmdir
+    raise PermissionError (WinError 5) even though we own the files.
+    """
+    os.chmod(path, stat.S_IWRITE)
+    func(path)
+
+
+def rmtree_robust(path: Path) -> None:
+    shutil.rmtree(path, onerror=_remove_readonly)
diff --git a/src/mkcd2app/utils/paths.py b/src/mkcd2app/utils/paths.py
index f0d6ab8..aabf229 100644
--- a/src/mkcd2app/utils/paths.py
+++ b/src/mkcd2app/utils/paths.py
@@ -1,27 +1,61 @@
-import os
-import shutil
-import stat
+from importlib.metadata import version
 from pathlib import Path
-from types import TracebackType
-from typing import Any
 
+from platformdirs import PlatformDirs
 
-def _remove_readonly(
-    func: Any,
-    path: str,
-    exc_info: tuple[type[BaseException], BaseException, TracebackType],
-) -> None:
-    """shutil.rmtree error handler: clear read-only bit and retry.
 
-    Needed on Windows because git marks files under .git/objects (and
-    sometimes .git itself) read-only, which makes os.unlink/os.rmdir
-    raise PermissionError (WinError 5) even though we own the files.
-    """
-    os.chmod(path, stat.S_IWRITE)
-    func(path)
+def get_mkcd2app_version() -> str:
+    return version("mkcd2app")
 
 
-def rmtree_robust(path: Path) -> None:
-    if not path.exists():
-        return
-    shutil.rmtree(path, onerror=_remove_readonly)
+DIRS = PlatformDirs("mkcd2app", appauthor=False)
+
+
+def get_user_data_dir() -> Path:
+    return Path(DIRS.user_data_dir) / get_mkcd2app_version()
+
+
+def get_user_state_dir() -> Path:
+    return Path(DIRS.user_state_dir) / get_mkcd2app_version()
+
+
+# Toolchain stuff
+
+
+def get_toolchain_dir() -> Path:
+    return get_user_data_dir() / "toolchain"
+
+
+def get_redun_db_for_toolchain_path() -> Path:
+    return get_user_state_dir() / "redun_db_for_toolchain.sqlite3"
+
+
+def get_js_tools_dir() -> Path:
+    return get_toolchain_dir() / "js_tools"
+
+
+def get_js_tools_bin_dir() -> Path:
+    return get_js_tools_dir() / "node_modules" / ".bin"
+
+
+def get_templates_npm_cache_dir() -> Path:
+    return get_toolchain_dir() / "templates_npm_cache"
+
+
+# Target stuff
+
+
+def get_target_dir() -> Path:
+    return get_user_data_dir() / "target"
+
+
+def get_redun_db_for_target_path() -> Path:
+    return get_user_state_dir() / "redun_db_for_target.sqlite3"
+
+
+def get_target_version_dir(v: str) -> Path:
+    return get_target_dir() / v
+
+
+def get_sim_html_path(v: str) -> Path:
+    return get_target_version_dir(v) / "---simulator.html"
diff --git a/src/mkcd2app/utils/resources.py b/src/mkcd2app/utils/resources.py
index 60efddb..aff6db0 100644
--- a/src/mkcd2app/utils/resources.py
+++ b/src/mkcd2app/utils/resources.py
@@ -5,14 +5,23 @@
 
 
 @contextmanager
-def get_template_path(name: str) -> Iterator[Path]:
-    ref = files("mkcd2app").joinpath("templates", name)
+def get_resource_template_path(name: str | None = None) -> Iterator[Path]:
+    ref = files("mkcd2app").joinpath("resources", "templates")
+    if name:
+        ref.joinpath(name)
     with as_file(ref) as path:
         yield path
 
 
 @contextmanager
-def get_js_tools_path() -> Iterator[Path]:
-    ref = files("mkcd2app").joinpath("js_tools")
+def get_resource_js_tools_path() -> Iterator[Path]:
+    ref = files("mkcd2app").joinpath("resources", "js_tools")
+    with as_file(ref) as path:
+        yield path
+
+
+@contextmanager
+def get_resource_empty_project_path() -> Iterator[Path]:
+    ref = files("mkcd2app").joinpath("resources", "empty_project")
     with as_file(ref) as path:
         yield path
diff --git a/src/mkcd2app/utils/run.py b/src/mkcd2app/utils/run.py
index 08721cb..5bd4b5c 100644
--- a/src/mkcd2app/utils/run.py
+++ b/src/mkcd2app/utils/run.py
@@ -22,7 +22,11 @@ def __init__(
         super().__init__(f"{command} failed ({return_code}) in {cwd}")
 
 
-def run_cmd(command: list[str], cwd: Path | str) -> str:
+def run_cmd(
+    command: list[str],
+    cwd: Path | str,
+    which_path: str | os.PathLike[str] | None = None,
+) -> str:
     """
     Runs a command (as a list, no shell) and captures its output.
 
@@ -32,11 +36,12 @@ def run_cmd(command: list[str], cwd: Path | str) -> str:
 
     :param command: The command as a list of arguments, e.g. ``["npm", "ci"]``.
     :param cwd: The working directory to execute the command in.
+    :param which_path: The path to pass to shutil.which, to search for the binary.
     :return: The stdout.
     :raises BuildError: If the command fails.
     :raises FileNotFoundError: If the executable cannot be found on PATH.
     """
-    resolved = shutil.which(command[0])
+    resolved = shutil.which(command[0], path=which_path)
     if resolved is None:
         raise FileNotFoundError(
             f"Executable '{command[0]}' not found on PATH. "
diff --git a/src/mkcd2app/utils/run_redun_task.py b/src/mkcd2app/utils/run_redun_task.py
new file mode 100644
index 0000000..af3b0c3
--- /dev/null
+++ b/src/mkcd2app/utils/run_redun_task.py
@@ -0,0 +1,27 @@
+import logging
+from pathlib import Path
+
+import redun
+from redun import Scheduler
+from redun.expression import Expression, Result
+
+from mkcd2app.utils.logger import create_logger
+
+logger = create_logger(name=__name__, level=logging.INFO)
+
+
+def run_redun_task(expr: Expression[Result] | Result, redun_db_path: Path) -> Result:
+    redun_db_path.parent.mkdir(parents=True, exist_ok=True)
+    db_uri = f"sqlite:///{redun_db_path.resolve()}"
+    logger.debug(f"redun cache DB: {db_uri}")
+    # noinspection PyUnresolvedReferences
+    redun_config = redun.config.Config(
+        {
+            "scheduler": {"log_level": "DEBUG"},
+            "backend": {"db_uri": db_uri},
+        }
+    )
+    scheduler = Scheduler(config=redun_config)
+    scheduler.load()
+    # TODO: don't forget to remove cache=False after done testing
+    return scheduler.run(expr, cache=False)
diff --git a/src/mkcd2app/utils/text.py b/src/mkcd2app/utils/text.py
new file mode 100644
index 0000000..48f1a77
--- /dev/null
+++ b/src/mkcd2app/utils/text.py
@@ -0,0 +1,39 @@
+import re
+from pathlib import Path
+
+from mkcd2app.models.metadata import BinaryJSMetadata
+
+
+def extract_meta_comment(file_path: Path) -> BinaryJSMetadata:
+    """
+    Extracts the // meta={} data from the binary.js file.
+
+    :param file_path: Path to the binary.js
+    :return: The metadata (a BinaryJSMetadata)
+    :raises ValueError: If the meta comment is not found in file.
+    """
+    with file_path.open("rt") as f:
+        for line in f:
+            line = line.strip()
+            if line.startswith("// meta="):
+                # Extract everything after '// meta='
+                json_str = line.split("// meta=", 1)[1]
+                return BinaryJSMetadata.model_validate_json(json_str)
+
+    raise ValueError("Meta comment not found in file.")
+
+
+# Thanks Gemini
+STRICT_NUMERIC_SEMVER = re.compile(r"^(0|[1-9]\d*)\.(0|[1-9]\d*)\.(0|[1-9]\d*)$")
+
+
+def is_strict_semver(version: str) -> bool:
+    """Validates string using official SemVer 2.0.0 regex pattern."""
+    return bool(STRICT_NUMERIC_SEMVER.match(version))
+
+
+def raise_for_invalid_strict_semver(version: str) -> None:
+    if not is_strict_semver(version):
+        raise ValueError(
+            f"Version '{version}' is not a valid strict numeric semver (e.g., 1.2.3)."
+        )
diff --git a/uv.lock b/uv.lock
index 60dbc3c..3212d6e 100644
--- a/uv.lock
+++ b/uv.lock
@@ -574,6 +574,7 @@ source = { editable = "." }
 dependencies = [
     { name = "beautifulsoup4" },
     { name = "pillow" },
+    { name = "platformdirs" },
     { name = "pydantic" },
     { name = "pyyaml" },
     { name = "redun" },
@@ -594,6 +595,7 @@ dev = [
 requires-dist = [
     { name = "beautifulsoup4" },
     { name = "pillow" },
+    { name = "platformdirs", specifier = ">=4.11.0" },
     { name = "pydantic" },
     { name = "pyyaml" },
     { name = "redun", specifier = "==0.44.1" },