diff --git a/justfile b/justfile
index 5eea5100f..5cc138e16 100644
--- a/justfile
+++ b/justfile
@@ -71,14 +71,34 @@ test-dotnet:
     @echo "=== Testing .NET code ==="
     @cd dotnet && dotnet test test/GitHub.Copilot.SDK.Test.csproj
 
-# Install all dependencies
-install:
-    @echo "=== Installing dependencies ==="
-    @cd nodejs && npm ci
-    @cd python && uv pip install -e ".[dev]"
+# Install all dependencies across all languages
+install: install-go install-python install-nodejs install-dotnet
+    @echo "✅ All dependencies installed"
+
+# Install Go dependencies and prerequisites for tests
+install-go: install-nodejs install-test-harness
+    @echo "=== Installing Go dependencies ==="
     @cd go && go mod download
+
+# Install Python dependencies and prerequisites for tests
+install-python: install-nodejs install-test-harness
+    @echo "=== Installing Python dependencies ==="
+    @cd python && uv venv && uv pip install -e ".[dev]"
+
+# Install .NET dependencies and prerequisites for tests
+install-dotnet: install-nodejs install-test-harness
+    @echo "=== Installing .NET dependencies ==="
     @cd dotnet && dotnet restore
-    @echo "✅ All dependencies installed"
+
+# Install Node.js dependencies
+install-nodejs:
+    @echo "=== Installing Node.js dependencies ==="
+    @cd nodejs && npm ci
+
+# Install test harness dependencies (used by E2E tests in all languages)
+install-test-harness:
+    @echo "=== Installing test harness dependencies ==="
+    @cd test/harness && npm ci
 
 # Run interactive SDK playground
 playground: