diff --git a/Cargo.lock b/Cargo.lock
index b6141435cc..9112dc4c10 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -3514,6 +3514,24 @@ dependencies = [
  "wit-component 0.20.3",
 ]
 
+[[package]]
+name = "extension_cli"
+version = "0.1.0"
+dependencies = [
+ "anyhow",
+ "clap 4.4.4",
+ "env_logger",
+ "extension",
+ "fs",
+ "language",
+ "log",
+ "theme",
+ "tokio",
+ "toml 0.8.10",
+ "tree-sitter",
+ "wasmtime",
+]
+
 [[package]]
 name = "extensions_ui"
 version = "0.1.0"
diff --git a/Cargo.toml b/Cargo.toml
index 1dc3c6cbfd..ff1fe93e4f 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -24,6 +24,7 @@ members = [
     "crates/editor",
     "crates/extension",
     "crates/extension_api",
+    "crates/extension_cli",
     "crates/extensions_ui",
     "crates/feature_flags",
     "crates/feedback",
@@ -273,6 +274,7 @@ time = { version = "0.3", features = [
     "formatting",
 ] }
 toml = "0.8"
+tokio = { version = "1", features = ["full"] }
 tower-http = "0.4.4"
 tree-sitter = { version = "0.20", features = ["wasm"] }
 tree-sitter-astro = { git = "https://github.com/virchau13/tree-sitter-astro.git", rev = "e924787e12e8a03194f36a113290ac11d6dc10f3" }
diff --git a/crates/collab/Cargo.toml b/crates/collab/Cargo.toml
index 0f4b706b5a..49cdcebbff 100644
--- a/crates/collab/Cargo.toml
+++ b/crates/collab/Cargo.toml
@@ -54,7 +54,7 @@ rustc-demangle.workspace = true
 telemetry_events.workspace = true
 text.workspace = true
 time.workspace = true
-tokio = { version = "1", features = ["full"] }
+tokio.workspace = true
 toml.workspace = true
 tower = "0.4"
 tower-http = { workspace = true, features = ["trace"] }
diff --git a/crates/extension/src/build_extension.rs b/crates/extension/src/extension_builder.rs
similarity index 95%
rename from crates/extension/src/build_extension.rs
rename to crates/extension/src/extension_builder.rs
index 0e1408d886..2de6c1057c 100644
--- a/crates/extension/src/build_extension.rs
+++ b/crates/extension/src/extension_builder.rs
@@ -6,9 +6,8 @@ use async_tar::Archive;
 use futures::io::BufReader;
 use futures::AsyncReadExt;
 use serde::Deserialize;
-use std::mem;
 use std::{
-    env, fs,
+    env, fs, mem,
     path::{Path, PathBuf},
     process::{Command, Stdio},
     sync::Arc,
@@ -72,22 +71,27 @@ impl ExtensionBuilder {
     pub async fn compile_extension(
         &self,
         extension_dir: &Path,
+        extension_manifest: &ExtensionManifest,
         options: CompileExtensionOptions,
     ) -> Result<()> {
+        if extension_dir.is_relative() {
+            bail!(
+                "extension dir {} is not an absolute path",
+                extension_dir.display()
+            );
+        }
+
         fs::create_dir_all(&self.cache_dir)?;
-        let extension_toml_path = extension_dir.join("extension.toml");
-        let extension_toml_content = fs::read_to_string(&extension_toml_path)?;
-        let extension_toml: ExtensionManifest = toml::from_str(&extension_toml_content)?;
 
         let cargo_toml_path = extension_dir.join("Cargo.toml");
-        if extension_toml.lib.kind == Some(ExtensionLibraryKind::Rust)
+        if extension_manifest.lib.kind == Some(ExtensionLibraryKind::Rust)
             || fs::metadata(&cargo_toml_path)?.is_file()
         {
             self.compile_rust_extension(extension_dir, options).await?;
         }
 
-        for (grammar_name, grammar_metadata) in extension_toml.grammars {
-            self.compile_grammar(extension_dir, grammar_name, grammar_metadata)
+        for (grammar_name, grammar_metadata) in &extension_manifest.grammars {
+            self.compile_grammar(extension_dir, grammar_name.as_ref(), grammar_metadata)
                 .await?;
         }
 
@@ -157,13 +161,13 @@ impl ExtensionBuilder {
     async fn compile_grammar(
         &self,
         extension_dir: &Path,
-        grammar_name: Arc<str>,
-        grammar_metadata: GrammarManifestEntry,
+        grammar_name: &str,
+        grammar_metadata: &GrammarManifestEntry,
     ) -> Result<()> {
         let clang_path = self.install_wasi_sdk_if_needed().await?;
 
         let mut grammar_repo_dir = extension_dir.to_path_buf();
-        grammar_repo_dir.extend(["grammars", grammar_name.as_ref()]);
+        grammar_repo_dir.extend(["grammars", grammar_name]);
 
         let mut grammar_wasm_path = grammar_repo_dir.clone();
         grammar_wasm_path.set_extension("wasm");
@@ -277,9 +281,10 @@ impl ExtensionBuilder {
                 );
             }
             bail!(
-                "failed to checkout revision {} in directory '{}'",
+                "failed to checkout revision {} in directory '{}': {}",
                 rev,
-                directory.display()
+                directory.display(),
+                String::from_utf8_lossy(&checkout_output.stderr)
             );
         }
 
diff --git a/crates/extension/src/extension_store.rs b/crates/extension/src/extension_store.rs
index 5b53b509a7..cb7190eb4d 100644
--- a/crates/extension/src/extension_store.rs
+++ b/crates/extension/src/extension_store.rs
@@ -1,4 +1,4 @@
-mod build_extension;
+pub mod extension_builder;
 mod extension_lsp_adapter;
 mod extension_manifest;
 mod wasm_host;
@@ -10,8 +10,8 @@ use crate::{extension_lsp_adapter::ExtensionLspAdapter, wasm_host::wit};
 use anyhow::{anyhow, bail, Context as _, Result};
 use async_compression::futures::bufread::GzipDecoder;
 use async_tar::Archive;
-use build_extension::{CompileExtensionOptions, ExtensionBuilder};
 use collections::{hash_map, BTreeMap, HashMap, HashSet};
+use extension_builder::{CompileExtensionOptions, ExtensionBuilder};
 use extension_manifest::ExtensionLibraryKind;
 use fs::{Fs, RemoveOptions};
 use futures::{
@@ -545,6 +545,7 @@ impl ExtensionStore {
                         builder
                             .compile_extension(
                                 &extension_source_path,
+                                &extension_manifest,
                                 CompileExtensionOptions { release: false },
                             )
                             .await
@@ -580,6 +581,7 @@ impl ExtensionStore {
     pub fn rebuild_dev_extension(&mut self, extension_id: Arc<str>, cx: &mut ModelContext<Self>) {
         let path = self.installed_dir.join(extension_id.as_ref());
         let builder = self.builder.clone();
+        let fs = self.fs.clone();
 
         match self.outstanding_operations.entry(extension_id.clone()) {
             hash_map::Entry::Occupied(_) => return,
@@ -588,8 +590,9 @@ impl ExtensionStore {
 
         cx.notify();
         let compile = cx.background_executor().spawn(async move {
+            let manifest = Self::load_extension_manifest(fs, &path).await?;
             builder
-                .compile_extension(&path, CompileExtensionOptions { release: true })
+                .compile_extension(&path, &manifest, CompileExtensionOptions { release: true })
                 .await
         });
 
@@ -1000,7 +1003,7 @@ impl ExtensionStore {
         Ok(())
     }
 
-    async fn load_extension_manifest(
+    pub async fn load_extension_manifest(
         fs: Arc<dyn Fs>,
         extension_dir: &Path,
     ) -> Result<ExtensionManifest> {
diff --git a/crates/extension_cli/Cargo.toml b/crates/extension_cli/Cargo.toml
new file mode 100644
index 0000000000..74e4d115f3
--- /dev/null
+++ b/crates/extension_cli/Cargo.toml
@@ -0,0 +1,23 @@
+[package]
+name = "extension_cli"
+version = "0.1.0"
+edition = "2021"
+publish = false
+license = "GPL-3.0-or-later"
+
+[lints]
+workspace = true
+
+[dependencies]
+anyhow.workspace = true
+clap = { workspace = true, features = ["derive"] }
+env_logger.workspace = true
+fs.workspace = true
+extension.workspace = true
+language.workspace = true
+log.workspace = true
+theme.workspace = true
+tokio.workspace = true
+toml.workspace = true
+tree-sitter.workspace = true
+wasmtime.workspace = true
diff --git a/crates/extension_cli/LICENSE-GPL b/crates/extension_cli/LICENSE-GPL
new file mode 120000
index 0000000000..89e542f750
--- /dev/null
+++ b/crates/extension_cli/LICENSE-GPL
@@ -0,0 +1 @@
+../../LICENSE-GPL
\ No newline at end of file
diff --git a/crates/extension_cli/src/main.rs b/crates/extension_cli/src/main.rs
new file mode 100644
index 0000000000..608aeaffd0
--- /dev/null
+++ b/crates/extension_cli/src/main.rs
@@ -0,0 +1,159 @@
+use std::{
+    collections::HashMap,
+    fs,
+    path::{Path, PathBuf},
+    sync::Arc,
+};
+
+use ::fs::{Fs, RealFs};
+use anyhow::{anyhow, Context, Result};
+use clap::Parser;
+use extension::{
+    extension_builder::{CompileExtensionOptions, ExtensionBuilder},
+    ExtensionStore,
+};
+use language::LanguageConfig;
+use theme::ThemeRegistry;
+use tree_sitter::{Language, Query, WasmStore};
+
+#[derive(Parser, Debug)]
+#[command(name = "zed-extension")]
+struct Args {
+    /// The path to the extension directory
+    extension_path: PathBuf,
+    /// Whether to compile with optimizations
+    #[arg(long)]
+    release: bool,
+    /// The path to a directory where build dependencies are downloaded
+    #[arg(long)]
+    scratch_dir: PathBuf,
+}
+
+#[tokio::main]
+async fn main() -> Result<()> {
+    env_logger::init();
+
+    let args = Args::parse();
+    let fs = Arc::new(RealFs);
+    let engine = wasmtime::Engine::default();
+    let mut wasm_store = WasmStore::new(engine)?;
+
+    let extension_path = args
+        .extension_path
+        .canonicalize()
+        .context("can't canonicalize extension_path")?;
+    let scratch_dir = args
+        .scratch_dir
+        .canonicalize()
+        .context("can't canonicalize scratch_dir")?;
+
+    let manifest = ExtensionStore::load_extension_manifest(fs.clone(), &extension_path).await?;
+    let builder = ExtensionBuilder::new(scratch_dir);
+    builder
+        .compile_extension(
+            &extension_path,
+            &manifest,
+            CompileExtensionOptions {
+                release: args.release,
+            },
+        )
+        .await?;
+
+    let grammars = test_grammars(&extension_path, &mut wasm_store)?;
+    test_languages(&extension_path, &grammars)?;
+    test_themes(&extension_path, fs.clone()).await?;
+
+    Ok(())
+}
+
+fn test_grammars(
+    extension_path: &Path,
+    wasm_store: &mut WasmStore,
+) -> Result<HashMap<String, Language>> {
+    let mut grammars = HashMap::default();
+    let grammars_dir = extension_path.join("grammars");
+    if !grammars_dir.exists() {
+        return Ok(grammars);
+    }
+
+    let entries = fs::read_dir(&grammars_dir)?;
+    for entry in entries {
+        let entry = entry?;
+        let grammar_path = entry.path();
+        let grammar_name = grammar_path.file_stem().unwrap().to_str().unwrap();
+        if grammar_path.extension() == Some("wasm".as_ref()) {
+            let wasm = fs::read(&grammar_path)?;
+            let language = wasm_store.load_language(grammar_name, &wasm)?;
+            log::info!("loaded grammar {grammar_name}");
+            grammars.insert(grammar_name.into(), language);
+        }
+    }
+
+    Ok(grammars)
+}
+
+fn test_languages(extension_path: &Path, grammars: &HashMap<String, Language>) -> Result<()> {
+    let languages_dir = extension_path.join("languages");
+    if !languages_dir.exists() {
+        return Ok(());
+    }
+
+    let entries = fs::read_dir(&languages_dir)?;
+    for entry in entries {
+        let entry = entry?;
+        let language_dir = entry.path();
+        let config_path = language_dir.join("config.toml");
+        let config_content = fs::read_to_string(&config_path)?;
+        let config: LanguageConfig = toml::from_str(&config_content)?;
+        let grammar = if let Some(name) = &config.grammar {
+            Some(
+                grammars
+                    .get(name.as_ref())
+                    .ok_or_else(|| anyhow!("language"))?,
+            )
+        } else {
+            None
+        };
+
+        let query_entries = fs::read_dir(&language_dir)?;
+        for entry in query_entries {
+            let entry = entry?;
+            let query_path = entry.path();
+            if query_path.extension() == Some("scm".as_ref()) {
+                let grammar = grammar.ok_or_else(|| {
+                    anyhow!(
+                        "language {} provides query {} but no grammar",
+                        config.name,
+                        query_path.display()
+                    )
+                })?;
+
+                let query_source = fs::read_to_string(&query_path)?;
+                let _query = Query::new(grammar, &query_source)?;
+            }
+        }
+
+        log::info!("loaded language {}", config.name);
+    }
+
+    Ok(())
+}
+
+async fn test_themes(extension_path: &Path, fs: Arc<dyn Fs>) -> Result<()> {
+    let themes_dir = extension_path.join("themes");
+    if !themes_dir.exists() {
+        return Ok(());
+    }
+
+    let entries = fs::read_dir(&themes_dir)?;
+    for entry in entries {
+        let entry = entry?;
+        let theme_path = entry.path();
+        if theme_path.extension() == Some("json".as_ref()) {
+            let theme_family = ThemeRegistry::read_user_theme(&entry.path(), fs.clone()).await?;
+            log::info!("loaded theme family {}", theme_family.name);
+        }
+    }
+
+    Ok(())
+}