diff --git a/src/build.rs b/src/build.rs
index 15f02de..5e07dc1 100644
--- a/src/build.rs
+++ b/src/build.rs
@@ -18,10 +18,12 @@ use console::style;
 use indicatif::{ProgressBar, ProgressStyle};
 use log::log_enabled;
 use serde::Serialize;
+use std::ffi::OsString;
 use std::fmt;
 use std::fs::File;
 use std::io::{stdout, Write};
 use std::path::PathBuf;
+use std::process::Stdio;
 use std::time::{Duration, Instant};
 
 use self::compile::compiler_args;
@@ -506,3 +508,18 @@ pub fn build(
         }
     }
 }
+
+pub fn pass_through_legacy(args: &[OsString]) -> i32 {
+    let project_root = helpers::get_abs_path(".");
+    let workspace_root = helpers::get_workspace_root(&project_root);
+
+    let bsb_path = helpers::get_rescript_legacy(&project_root, workspace_root);
+
+    let status = std::process::Command::new(bsb_path)
+        .args(args)
+        .stdout(Stdio::inherit())
+        .stderr(Stdio::inherit())
+        .status();
+
+    status.map(|s| s.code().unwrap_or(1)).unwrap_or(1)
+}
diff --git a/src/build/clean.rs b/src/build/clean.rs
index ba53e4f..5792b09 100644
--- a/src/build/clean.rs
+++ b/src/build/clean.rs
@@ -338,7 +338,7 @@ pub fn cleanup_after_build(build_state: &BuildState) {
     });
 }
 
-pub fn clean(path: &str, show_progress: bool, bsc_path: Option<String>, build_dev_deps: bool) -> Result<()> {
+pub fn clean(path: &str, show_progress: bool, bsc_path: Option<String>) -> Result<()> {
     let project_root = helpers::get_abs_path(path);
     let workspace_root = helpers::get_workspace_root(&project_root);
     let packages = packages::make(
@@ -346,8 +346,9 @@ pub fn clean(path: &str, show_progress: bool, bsc_path: Option<String>, build_de
         &project_root,
         &workspace_root,
         show_progress,
-        // Always clean dev dependencies
-        build_dev_deps,
+        // Build the package tree with dev dependencies.
+        // They should always be cleaned if they are there.
+        true,
     )?;
     let root_config_name = packages::read_package_name(&project_root)?;
     let bsc_path = match bsc_path {
diff --git a/src/cli.rs b/src/cli.rs
new file mode 100644
index 0000000..13fb1f1
--- /dev/null
+++ b/src/cli.rs
@@ -0,0 +1,166 @@
+use std::ffi::OsString;
+
+use clap::{Args, Parser, Subcommand};
+use clap_verbosity_flag::InfoLevel;
+
+/// Rewatch is an alternative build system for the Rescript Compiler bsb (which uses Ninja internally). It strives
+/// to deliver consistent and faster builds in monorepo setups with multiple packages, where the
+/// default build system fails to pick up changed interfaces across multiple packages.
+#[derive(Parser, Debug)]
+#[command(version)]
+#[command(args_conflicts_with_subcommands = true)]
+pub struct Cli {
+    /// Verbosity:
+    /// -v -> Debug
+    /// -vv -> Trace
+    /// -q -> Warn
+    /// -qq -> Error
+    /// -qqq -> Off.
+    /// Default (/ no argument given): 'info'
+    #[command(flatten)]
+    pub verbose: clap_verbosity_flag::Verbosity<InfoLevel>,
+
+    /// The command to run. If not provided it will default to build.
+    #[command(subcommand)]
+    pub command: Option<Command>,
+
+    /// The relative path to where the main rescript.json resides. IE - the root of your project.
+    #[arg(default_value = ".")]
+    pub folder: String,
+
+    #[command(flatten)]
+    pub build_args: BuildArgs,
+}
+
+#[derive(Args, Debug, Clone)]
+pub struct BuildArgs {
+    /// Filter files by regex
+    ///
+    /// Filter allows for a regex to be supplied which will filter the files to be compiled. For
+    /// instance, to filter out test files for compilation while doing feature work.
+    #[arg(short, long)]
+    pub filter: Option<String>,
+
+    /// Action after build
+    ///
+    /// This allows one to pass an additional command to the watcher, which allows it to run when
+    /// finished. For instance, to play a sound when done compiling, or to run a test suite.
+    /// NOTE - You may need to add '--color=always' to your subcommand in case you want to output
+    /// colour as well
+    #[arg(short, long)]
+    pub after_build: Option<String>,
+
+    /// Create source_dirs.json
+    ///
+    /// This creates a source_dirs.json file at the root of the monorepo, which is needed when you
+    /// want to use Reanalyze
+    #[arg(short, long, default_value_t = false, num_args = 0..=1)]
+    pub create_sourcedirs: bool,
+
+    /// Build development dependencies
+    ///
+    /// This is the flag to also compile development dependencies
+    /// It's important to know that we currently do not discern between project src, and
+    /// dependencies. So enabling this flag will enable building _all_ development dependencies of
+    /// _all_ packages
+    #[arg(long, default_value_t = false, num_args = 0..=1)]
+    pub dev: bool,
+
+    /// Disable timing on the output
+    #[arg(short, long, default_value_t = false, num_args = 0..=1)]
+    pub no_timing: bool,
+
+    /// Path to bsc
+    #[arg(long)]
+    pub bsc_path: Option<String>,
+}
+
+#[derive(Args, Debug)]
+pub struct WatchArgs {
+    /// Filter files by regex
+    ///
+    /// Filter allows for a regex to be supplied which will filter the files to be compiled. For
+    /// instance, to filter out test files for compilation while doing feature work.
+    #[arg(short, long)]
+    pub filter: Option<String>,
+
+    /// Action after build
+    ///
+    /// This allows one to pass an additional command to the watcher, which allows it to run when
+    /// finished. For instance, to play a sound when done compiling, or to run a test suite.
+    /// NOTE - You may need to add '--color=always' to your subcommand in case you want to output
+    /// colour as well
+    #[arg(short, long)]
+    pub after_build: Option<String>,
+
+    /// Create source_dirs.json
+    ///
+    /// This creates a source_dirs.json file at the root of the monorepo, which is needed when you
+    /// want to use Reanalyze
+    #[arg(short, long, default_value_t = false, num_args = 0..=1)]
+    pub create_sourcedirs: bool,
+
+    /// Build development dependencies
+    ///
+    /// This is the flag to also compile development dependencies
+    /// It's important to know that we currently do not discern between project src, and
+    /// dependencies. So enabling this flag will enable building _all_ development dependencies of
+    /// _all_ packages
+    #[arg(long, default_value_t = false, num_args = 0..=1)]
+    pub dev: bool,
+
+    /// Path to bsc
+    #[arg(long)]
+    pub bsc_path: Option<String>,
+}
+
+#[derive(Subcommand, Debug)]
+pub enum Command {
+    /// Build using Rewatch
+    Build(BuildArgs),
+    /// Build, then start a watcher
+    Watch(WatchArgs),
+    /// Clean the build artifacts
+    Clean {
+        /// Path to bsc
+        #[arg(long)]
+        bsc_path: Option<String>,
+    },
+    /// Alias to `legacy format`.
+    #[command(disable_help_flag = true)]
+    Format {
+        #[arg(allow_hyphen_values = true, num_args = 0..)]
+        format_args: Vec<OsString>,
+    },
+    /// Alias to `legacy dump`.
+    #[command(disable_help_flag = true)]
+    Dump {
+        #[arg(allow_hyphen_values = true, num_args = 0..)]
+        dump_args: Vec<OsString>,
+    },
+    /// This prints the compiler arguments. It expects the path to a rescript.json file.
+    CompilerArgs {
+        /// Path to a rescript.json file
+        #[command()]
+        path: String,
+
+        #[arg(long, default_value_t = false, num_args = 0..=1)]
+        dev: bool,
+
+        /// To be used in conjunction with compiler_args
+        #[arg(long)]
+        rescript_version: Option<String>,
+
+        /// A custom path to bsc
+        #[arg(long)]
+        bsc_path: Option<String>,
+    },
+    /// Use the legacy build system.
+    ///
+    /// After this command is encountered, the rest of the arguments are passed to the legacy build system.
+    #[command(disable_help_flag = true)]
+    Legacy {
+        #[arg(allow_hyphen_values = true, num_args = 0..)]
+        legacy_args: Vec<OsString>,
+    },
+}
diff --git a/src/helpers.rs b/src/helpers.rs
index c4a7343..3f98628 100644
--- a/src/helpers.rs
+++ b/src/helpers.rs
@@ -150,6 +150,25 @@ pub fn create_path_for_path(path: &Path) {
     fs::DirBuilder::new().recursive(true).create(path).unwrap();
 }
 
+pub fn get_rescript_legacy(root_path: &str, workspace_root: Option<String>) -> String {
+    match (
+        PathBuf::from(format!("{}/node_modules/rescript/rescript-legacy", root_path)).canonicalize(),
+        workspace_root.map(|workspace_root| {
+            PathBuf::from(format!(
+                "{}/node_modules/rescript/rescript-legacy",
+                workspace_root
+            ))
+            .canonicalize()
+        }),
+    ) {
+        (Ok(path), _) => path,
+        (_, Some(Ok(path))) => path,
+        _ => panic!("Could not find rescript-legacy"),
+    }
+    .to_string_lossy()
+    .to_string()
+}
+
 pub fn get_bsc(root_path: &str, workspace_root: Option<String>) -> String {
     let subfolder = match (std::env::consts::OS, std::env::consts::ARCH) {
         ("macos", "aarch64") => "darwinarm64",
diff --git a/src/lib.rs b/src/lib.rs
index 9dc6f55..2df92a4 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,4 +1,5 @@
 pub mod build;
+pub mod cli;
 pub mod cmd;
 pub mod config;
 pub mod helpers;
diff --git a/src/main.rs b/src/main.rs
index 3ff4768..be5f97f 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,88 +1,14 @@
 use anyhow::Result;
-use clap::{Parser, ValueEnum};
-use clap_verbosity_flag::InfoLevel;
+use clap::Parser;
 use log::LevelFilter;
 use regex::Regex;
-use std::io::Write;
+use std::{ffi::OsString, io::Write};
 
-use rewatch::{build, cmd, lock, watcher};
-
-#[derive(Debug, Clone, ValueEnum)]
-enum Command {
-    /// Build using Rewatch
-    Build,
-    /// Build, then start a watcher
-    Watch,
-    /// Clean the build artifacts
-    Clean,
-}
-
-/// Rewatch is an alternative build system for the Rescript Compiler bsb (which uses Ninja internally). It strives
-/// to deliver consistent and faster builds in monorepo setups with multiple packages, where the
-/// default build system fails to pick up changed interfaces across multiple packages.
-#[derive(Parser, Debug)]
-#[command(version)]
-struct Args {
-    #[arg(value_enum)]
-    command: Option<Command>,
-
-    /// The relative path to where the main rescript.json resides. IE - the root of your project.
-    folder: Option<String>,
-
-    /// Filter allows for a regex to be supplied which will filter the files to be compiled. For
-    /// instance, to filter out test files for compilation while doing feature work.
-    #[arg(short, long)]
-    filter: Option<String>,
-
-    /// This allows one to pass an additional command to the watcher, which allows it to run when
-    /// finished. For instance, to play a sound when done compiling, or to run a test suite.
-    /// NOTE - You may need to add '--color=always' to your subcommand in case you want to output
-    /// colour as well
-    #[arg(short, long)]
-    after_build: Option<String>,
-
-    // Disable timing on the output
-    #[arg(short, long, default_value = "false", num_args = 0..=1)]
-    no_timing: bool,
-
-    /// Verbosity:
-    /// -v -> Debug
-    /// -vv -> Trace
-    /// -q -> Warn
-    /// -qq -> Error
-    /// -qqq -> Off.
-    /// Default (/ no argument given): 'info'
-    #[command(flatten)]
-    verbose: clap_verbosity_flag::Verbosity<InfoLevel>,
-
-    /// This creates a source_dirs.json file at the root of the monorepo, which is needed when you
-    /// want to use Reanalyze
-    #[arg(short, long, default_value_t = false, num_args = 0..=1)]
-    create_sourcedirs: bool,
-
-    /// This prints the compiler arguments. It expects the path to a rescript.json file.
-    /// This also requires --bsc-path and --rescript-version to be present
-    #[arg(long)]
-    compiler_args: Option<String>,
-
-    /// This is the flag to also compile development dependencies
-    /// It's important to know that we currently do not discern between project src, and
-    /// dependencies. So enabling this flag will enable building _all_ development dependencies of
-    /// _all_ packages
-    #[arg(long, default_value_t = false, num_args = 0..=1)]
-    dev: bool,
-
-    /// To be used in conjunction with compiler_args
-    #[arg(long)]
-    rescript_version: Option<String>,
-
-    /// A custom path to bsc
-    #[arg(long)]
-    bsc_path: Option<String>,
-}
+use rewatch::{build, cli, cmd, lock, watcher};
 
 fn main() -> Result<()> {
-    let args = Args::parse();
+    let args = cli::Cli::parse();
+
     let log_level_filter = args.verbose.log_level_filter();
 
     env_logger::Builder::new()
@@ -91,69 +17,100 @@ fn main() -> Result<()> {
         .target(env_logger::fmt::Target::Stdout)
         .init();
 
-    let command = args.command.unwrap_or(Command::Build);
-    let folder = args.folder.unwrap_or(".".to_string());
-    let filter = args
-        .filter
-        .map(|filter| Regex::new(filter.as_ref()).expect("Could not parse regex"));
+    let command = args.command.unwrap_or(cli::Command::Build(args.build_args));
 
-    match args.compiler_args {
-        None => (),
-        Some(path) => {
+    // handle those commands early, because we don't need a lock for them
+    match &command {
+        cli::Command::Legacy { legacy_args } => {
+            let code = build::pass_through_legacy(legacy_args);
+            std::process::exit(code);
+        }
+        cli::Command::Format { format_args } => {
+            let mut args: Vec<OsString> = vec!["format".into()];
+            args.append(&mut format_args.clone());
+            let code = build::pass_through_legacy(args.as_slice());
+            std::process::exit(code);
+        }
+        cli::Command::Dump { dump_args } => {
+            let mut args: Vec<OsString> = vec!["dump".into()];
+            args.append(&mut dump_args.clone());
+            let code = build::pass_through_legacy(args.as_slice());
+            std::process::exit(code);
+        }
+        cli::Command::CompilerArgs {
+            path,
+            dev,
+            rescript_version,
+            bsc_path,
+        } => {
             println!(
                 "{}",
-                build::get_compiler_args(&path, args.rescript_version, args.bsc_path, args.dev)?
+                build::get_compiler_args(&path, rescript_version.clone(), bsc_path.clone(), *dev)?
             );
             std::process::exit(0);
         }
+        _ => (),
     }
 
     // The 'normal run' mode will show the 'pretty' formatted progress. But if we turn off the log
     // level, we should never show that.
     let show_progress = log_level_filter == LevelFilter::Info;
 
-    match lock::get(&folder) {
+    match lock::get(&args.folder) {
         lock::Lock::Error(ref e) => {
             println!("Could not start Rewatch: {e}");
             std::process::exit(1)
         }
         lock::Lock::Aquired(_) => match command {
-            Command::Clean => build::clean::clean(&folder, show_progress, args.bsc_path, args.dev),
-            Command::Build => {
+            cli::Command::Clean { bsc_path } => build::clean::clean(&args.folder, show_progress, bsc_path),
+            cli::Command::Build(build_args) => {
+                let filter = build_args
+                    .filter
+                    .map(|filter| Regex::new(filter.as_ref()).expect("Could not parse regex"));
+
                 match build::build(
                     &filter,
-                    &folder,
+                    &args.folder,
                     show_progress,
-                    args.no_timing,
-                    args.create_sourcedirs,
-                    args.bsc_path,
-                    args.dev,
+                    build_args.no_timing,
+                    build_args.create_sourcedirs,
+                    build_args.bsc_path,
+                    build_args.dev,
                 ) {
                     Err(e) => {
                         println!("{e}");
                         std::process::exit(1)
                     }
                     Ok(_) => {
-                        if let Some(args_after_build) = args.after_build {
+                        if let Some(args_after_build) = build_args.after_build {
                             cmd::run(args_after_build)
                         }
                         std::process::exit(0)
                     }
                 };
             }
-            Command::Watch => {
+            cli::Command::Watch(watch_args) => {
+                let filter = watch_args
+                    .filter
+                    .map(|filter| Regex::new(filter.as_ref()).expect("Could not parse regex"));
                 watcher::start(
                     &filter,
                     show_progress,
-                    &folder,
-                    args.after_build,
-                    args.create_sourcedirs,
-                    args.dev,
-                    args.bsc_path,
+                    &args.folder,
+                    watch_args.after_build,
+                    watch_args.create_sourcedirs,
+                    watch_args.dev,
+                    watch_args.bsc_path,
                 );
 
                 Ok(())
             }
+            cli::Command::CompilerArgs { .. }
+            | cli::Command::Legacy { .. }
+            | cli::Command::Format { .. }
+            | cli::Command::Dump { .. } => {
+                unreachable!("command already handled")
+            }
         },
     }
 }
diff --git a/tests/compile.sh b/tests/compile.sh
index dd39bf5..447bc9c 100755
--- a/tests/compile.sh
+++ b/tests/compile.sh
@@ -33,36 +33,36 @@ fi
 node ./packages/main/src/Main.mjs > ./packages/main/src/output.txt
 
 mv ./packages/main/src/Main.res ./packages/main/src/Main2.res
-rewatch build &> ../tests/snapshots/rename-file.txt
+rewatch build --no-timing &> ../tests/snapshots/rename-file.txt
 mv ./packages/main/src/Main2.res ./packages/main/src/Main.res
 
 # Rename a file with a dependent - this should trigger an error
 mv ./packages/main/src/InternalDep.res ./packages/main/src/InternalDep2.res
-rewatch build &> ../tests/snapshots/rename-file-internal-dep.txt
+rewatch build --no-timing &> ../tests/snapshots/rename-file-internal-dep.txt
 # replace the absolute path so the snapshot is the same on all machines
 replace "s/$(pwd | sed "s/\//\\\\\//g")//g" ../tests/snapshots/rename-file-internal-dep.txt
 mv ./packages/main/src/InternalDep2.res ./packages/main/src/InternalDep.res
 
 # Rename a file with a dependent in a namespaced package - this should trigger an error (regression)
 mv ./packages/new-namespace/src/Other_module.res ./packages/new-namespace/src/Other_module2.res
-rewatch build &> ../tests/snapshots/rename-file-internal-dep-namespace.txt
+rewatch build --no-timing &> ../tests/snapshots/rename-file-internal-dep-namespace.txt
 # replace the absolute path so the snapshot is the same on all machines
 replace "s/$(pwd | sed "s/\//\\\\\//g")//g" ../tests/snapshots/rename-file-internal-dep-namespace.txt
 mv ./packages/new-namespace/src/Other_module2.res ./packages/new-namespace/src/Other_module.res
 
 rewatch build &>  /dev/null
 mv ./packages/main/src/ModuleWithInterface.resi ./packages/main/src/ModuleWithInterface2.resi
-rewatch build &> ../tests/snapshots/rename-interface-file.txt
+rewatch build --no-timing &> ../tests/snapshots/rename-interface-file.txt
 mv ./packages/main/src/ModuleWithInterface2.resi ./packages/main/src/ModuleWithInterface.resi
 rewatch build &> /dev/null
 mv ./packages/main/src/ModuleWithInterface.res ./packages/main/src/ModuleWithInterface2.res
-rewatch build &> ../tests/snapshots/rename-file-with-interface.txt
+rewatch build --no-timing &> ../tests/snapshots/rename-file-with-interface.txt
 mv ./packages/main/src/ModuleWithInterface2.res ./packages/main/src/ModuleWithInterface.res
 rewatch build &> /dev/null
 
 # when deleting a file that other files depend on, the compile should fail
 rm packages/dep02/src/Dep02.res
-rewatch build &> ../tests/snapshots/remove-file.txt
+rewatch build --no-timing &> ../tests/snapshots/remove-file.txt
 # replace the absolute path so the snapshot is the same on all machines
 replace "s/$(pwd | sed "s/\//\\\\\//g")//g" ../tests/snapshots/remove-file.txt
 git checkout -- packages/dep02/src/Dep02.res
@@ -70,7 +70,7 @@ rewatch build &> /dev/null
 
 # it should show an error when we have a dependency cycle
 echo 'Dep01.log()' >> packages/new-namespace/src/NS_alias.res
-rewatch build &> ../tests/snapshots/dependency-cycle.txt
+rewatch build --no-timing &> ../tests/snapshots/dependency-cycle.txt
 git checkout -- packages/new-namespace/src/NS_alias.res
 
 # it should compile dev dependencies with the --dev flag
@@ -91,7 +91,7 @@ else
   exit 1
 fi
 
-rewatch clean --dev &> /dev/null
+rewatch clean &> /dev/null
 file_count=$(find ./packages/with-dev-deps -name *.mjs | wc -l)
 if [ "$file_count" -eq 0 ];
 then
diff --git a/tests/utils.sh b/tests/utils.sh
index f2ee211..8ddca1b 100644
--- a/tests/utils.sh
+++ b/tests/utils.sh
@@ -3,8 +3,8 @@ overwrite() { echo -e "\r\033[1A\033[0K$@"; }
 success() { echo -e "- ✅ \033[32m$1\033[0m"; }
 error() { echo -e "- 🛑 \033[31m$1\033[0m"; }
 bold() { echo -e "\033[1m$1\033[0m"; }
-rewatch() { RUST_BACKTRACE=1 $REWATCH_EXECUTABLE --no-timing=true $@; }
-rewatch_bg() { RUST_BACKTRACE=1 nohup $REWATCH_EXECUTABLE --no-timing=true $@; }
+rewatch() { RUST_BACKTRACE=1 $REWATCH_EXECUTABLE $@; }
+rewatch_bg() { RUST_BACKTRACE=1 nohup $REWATCH_EXECUTABLE $@; }
 
 replace() {
   if [[ $OSTYPE == 'darwin'* ]];