4 files changed, 26 insertions, 1 deletions
diff --git a/tvix/Cargo.lock b/tvix/Cargo.lock
index 430d369a1bee..7d3b52a3051c 100644
--- a/tvix/Cargo.lock
+++ b/tvix/Cargo.lock
@@ -3317,6 +3317,7 @@ dependencies = [
  "thiserror",
  "tokio",
  "tracing",
+ "tracing-subscriber",
  "tvix-build",
  "tvix-castore",
  "tvix-eval",
diff --git a/tvix/Cargo.nix b/tvix/Cargo.nix
index 4e6c037d0f52..3e74c4776e4d 100644
--- a/tvix/Cargo.nix
+++ b/tvix/Cargo.nix
@@ -10381,6 +10381,11 @@ rec {
             packageId = "tracing";
           }
           {
+            name = "tracing-subscriber";
+            packageId = "tracing-subscriber";
+            features = [ "json" ];
+          }
+          {
             name = "tvix-build";
             packageId = "tvix-build";
           }
diff --git a/tvix/cli/Cargo.toml b/tvix/cli/Cargo.toml
index f8101300b194..81e28c4c7cf0 100644
--- a/tvix/cli/Cargo.toml
+++ b/tvix/cli/Cargo.toml
@@ -19,8 +19,9 @@ clap = { version = "4.0", features = ["derive", "env"] }
 dirs = "4.0.0"
 rustyline = "10.0.0"
 thiserror = "1.0.38"
-tracing = "0.1.37"
 tokio = "1.28.0"
+tracing = "0.1.37"
+tracing-subscriber = { version = "0.3.16", features = ["json"] }
 
 [dependencies.wu-manber]
 git = "https://github.com/tvlfyi/wu-manber.git"
diff --git a/tvix/cli/src/main.rs b/tvix/cli/src/main.rs
index da09ab878954..24b180c1f289 100644
--- a/tvix/cli/src/main.rs
+++ b/tvix/cli/src/main.rs
@@ -2,6 +2,9 @@ use clap::Parser;
 use rustyline::{error::ReadlineError, Editor};
 use std::rc::Rc;
 use std::{fs, path::PathBuf};
+use tracing::Level;
+use tracing_subscriber::fmt::writer::MakeWriterExt;
+use tracing_subscriber::{layer::SubscriberExt, util::SubscriberInitExt};
 use tvix_build::buildservice;
 use tvix_eval::builtins::impure_builtins;
 use tvix_eval::observer::{DisassemblingObserver, TracingObserver};
@@ -12,6 +15,9 @@ use tvix_glue::{builtins::add_derivation_builtins, configure_nix_path};
 
 #[derive(Parser)]
 struct Args {
+    #[arg(long)]
+    log_level: Option<Level>,
+
     /// Path to a script to evaluate
     script: Option<PathBuf>,
 
@@ -213,6 +219,18 @@ fn lint(code: &str, path: Option<PathBuf>, args: &Args) -> bool {
 fn main() {
     let args = Args::parse();
 
+    // configure log settings
+    let level = args.log_level.unwrap_or(Level::INFO);
+
+    let subscriber = tracing_subscriber::registry().with(
+        tracing_subscriber::fmt::Layer::new()
+            .with_writer(std::io::stderr.with_max_level(level))
+            .pretty(),
+    );
+    subscriber
+        .try_init()
+        .expect("unable to set up tracing subscriber");
+
     if let Some(file) = &args.script {
         run_file(file.clone(), &args)
     } else if let Some(expr) = &args.expr {