diff --git a/.codex/build_all_targets.sh b/.codex/build_all_targets.sh
new file mode 100644
index 0000000..de68986
--- /dev/null
+++ b/.codex/build_all_targets.sh
@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+
+CODEX_DIR=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)
+cd $CODEX_DIR
+
+pushd ..
+  just build-extension
+popd
diff --git a/.codex/deps_src/AGENTS.md b/.codex/deps_src/AGENTS.md
new file mode 100644
index 0000000..6e81be2
--- /dev/null
+++ b/.codex/deps_src/AGENTS.md
@@ -0,0 +1,2 @@
+This directory contains cloned repositories with source code for some
+of the development dependencies. This might be useful as a reference.
diff --git a/.codex/internet_resources/download.sh b/.codex/internet_resources/download.sh
new file mode 100755
index 0000000..a839cda
--- /dev/null
+++ b/.codex/internet_resources/download.sh
@@ -0,0 +1,9 @@
+#!/usr/bin/env bash
+
+DOWNLOADS_DIR=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)
+cd $DOWNLOADS_DIR
+
+# Download the specification of the CodeTracer trace json format.
+# Read the trace_json_spec.md file to understand what json records
+# should be produced by the tracers in this repo.
+wget https://raw.githubusercontent.com/metacraft-labs/runtime_tracing/refs/heads/master/docs/trace_json_spec.md
diff --git a/.codex/setup.sh b/.codex/setup.sh
new file mode 100755
index 0000000..9c917e1
--- /dev/null
+++ b/.codex/setup.sh
@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+
+CODEX_DIR=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)
+cd $CODEX_DIR
+
+apt-get update
+apt-get install -y --no-install-recommends just
+
+pushd deps_src
+  git clone https://github.com/metacraft-labs/runtime_tracing
+popd
+
+./build_all_targets.sh
+
diff --git a/.gitignore b/.gitignore
index 6b2dc2f..f10aa8e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,3 +4,4 @@
 !test/benchmarks/fixtures/*.json
 test/tmp/
 .direnv/
+pkg/
diff --git a/AGENTS.md b/AGENTS.md
index 484df08..bd72af2 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -1,9 +1,15 @@
 # Instructions for Codex
 
+To build the Rust native extension, execute:
+
+```
+just build-extension
+```
+
 To run the test suite, execute:
 
 ```
-ruby -Itest test/test_tracer.rb
+just test
 ```
 
 The tester executes a number of sample programs in `test/programs` and compares their outputs to the fixtures in `test/fixtures`.
@@ -11,9 +17,39 @@ The tester executes a number of sample programs in `test/programs` and compares
 To run the benchmark, execute:
 
 ```
-ruby test/benchmarks/run_benchmark.rb heavy_work
+just bench
 ```
 
+# You don't have access to the internet
+
+During development, certain commands will fail because you don't have
+access to the intenet.
+
+The script `.codex/internet_resources/download.sh` is executed before
+your development session stars while your computer is still connected
+to the internet.
+
+You can examine this script to see what kind of internet resources
+have been downloaded for offline use. If it's difficult for you to
+achieve a task without access to additional internet resources, you
+can always propose a PR that modifies the download.sh script instead
+of completing your main task.
+
+Downloading development dependencies may also fail due to the lack of
+internet connectivity. We are trying to maintain the script `.codex/build_all_targets.sh`
+that is also executed before your development session starts while
+your computer is still connected to the internet. It tries to run
+all build commands that need development dependencies in order to
+cache the dependencies for offline use. Please propose changes to
+this script when you introduce new build targets with dependencies.
+
+When you need to consult the documentation or source code modules
+for a particular dependency, always try to find where this dependency
+have been downloaded and try to access the necessary files through
+the file system (i.e. depending on the programming language, the
+operating system and the package manager being used, they should
+be in their standard location).
+
 # Code quality guidelines
 
 - Strive to achieve high code quality.
diff --git a/Justfile b/Justfile
index 7eb2d92..ab8a6a1 100644
--- a/Justfile
+++ b/Justfile
@@ -5,3 +5,6 @@ test:
 
 bench name="heavy_work":
     ruby test/benchmarks/run_benchmark.rb {{name}}
+
+build-extension:
+    cargo build --release --manifest-path ext/native_tracer/Cargo.toml
diff --git a/Rakefile b/Rakefile
new file mode 100644
index 0000000..4ebda76
--- /dev/null
+++ b/Rakefile
@@ -0,0 +1,7 @@
+require 'rb_sys/extensiontask'
+
+RbSys::ExtensionTask.new('codetracer_ruby_recorder') do |ext|
+  ext.ext_dir = 'ext/native_tracer'
+  ext.lib_dir = 'src'
+  ext.gem_spec = Gem::Specification.load('codetracer-ruby-recorder.gemspec')
+end
diff --git a/codetracer-ruby-recorder.gemspec b/codetracer-ruby-recorder.gemspec
new file mode 100644
index 0000000..4f01849
--- /dev/null
+++ b/codetracer-ruby-recorder.gemspec
@@ -0,0 +1,17 @@
+Gem::Specification.new do |spec|
+  spec.name          = 'codetracer-ruby-recorder'
+  spec.version       = '0.1.0'
+  spec.authors       = ['Metacraft Labs']
+  spec.email         = ['info@metacraft-labs.com']
+
+  spec.summary       = 'CodeTracer Ruby recorder with native extension'
+  spec.description   = 'Ruby tracer that records execution steps via a Rust native extension.'
+  spec.license       = 'MIT'
+  spec.homepage      = 'https://github.com/metacraft-labs/codetracer-ruby-recorder'
+
+  spec.files         = Dir['src/**/*', 'ext/native_tracer/**/{Cargo.toml,*.rs}', 'ext/native_tracer/extconf.rb', 'README.md', 'LICENSE']
+  spec.require_paths = ['src']
+  spec.extensions    = ['ext/native_tracer/extconf.rb']
+
+  spec.add_development_dependency 'rb_sys', '~> 0.9'
+end
diff --git a/ext/native_tracer/.gitignore b/ext/native_tracer/.gitignore
new file mode 100644
index 0000000..2f7896d
--- /dev/null
+++ b/ext/native_tracer/.gitignore
@@ -0,0 +1 @@
+target/
diff --git a/ext/native_tracer/Cargo.lock b/ext/native_tracer/Cargo.lock
new file mode 100644
index 0000000..a79211c
--- /dev/null
+++ b/ext/native_tracer/Cargo.lock
@@ -0,0 +1,414 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "aho-corasick"
+version = "1.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8e60d3430d3a69478ad0993f19238d2df97c507009a52b3c10addcd7f6bcb916"
+dependencies = [
+ "memchr",
+]
+
+[[package]]
+name = "autocfg"
+version = "1.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ace50bade8e6234aa140d9a2f552bbee1db4d353f69b8217bc503490fc1a9f26"
+
+[[package]]
+name = "bindgen"
+version = "0.69.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "271383c67ccabffb7381723dea0672a673f292304fcb45c01cc648c7a8d58088"
+dependencies = [
+ "bitflags",
+ "cexpr",
+ "clang-sys",
+ "itertools",
+ "lazy_static",
+ "lazycell",
+ "proc-macro2",
+ "quote",
+ "regex",
+ "rustc-hash",
+ "shlex",
+ "syn",
+]
+
+[[package]]
+name = "bitflags"
+version = "2.9.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1b8e56985ec62d17e9c1001dc89c88ecd7dc08e47eba5ec7c29c7b5eeecde967"
+
+[[package]]
+name = "cexpr"
+version = "0.6.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6fac387a98bb7c37292057cffc56d62ecb629900026402633ae9160df93a8766"
+dependencies = [
+ "nom",
+]
+
+[[package]]
+name = "cfg-if"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
+
+[[package]]
+name = "clang-sys"
+version = "1.8.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0b023947811758c97c59bf9d1c188fd619ad4718dcaa767947df1cadb14f39f4"
+dependencies = [
+ "glob",
+ "libc",
+ "libloading",
+]
+
+[[package]]
+name = "codetracer_ruby_recorder"
+version = "0.1.0"
+dependencies = [
+ "rb-sys",
+ "rb-sys-env",
+ "runtime_tracing",
+]
+
+[[package]]
+name = "either"
+version = "1.15.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "48c757948c5ede0e46177b7add2e67155f70e33c07fea8284df6576da70b3719"
+
+[[package]]
+name = "glob"
+version = "0.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a8d1add55171497b4705a648c6b583acafb01d58050a51727785f0b2c8e0a2b2"
+
+[[package]]
+name = "itertools"
+version = "0.12.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ba291022dbbd398a455acf126c1e341954079855bc60dfdda641363bd6922569"
+dependencies = [
+ "either",
+]
+
+[[package]]
+name = "itoa"
+version = "1.0.15"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4a5f13b858c8d314ee3e8f639011f7ccefe71f97f96e50151fb991f267928e2c"
+
+[[package]]
+name = "lazy_static"
+version = "1.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bbd2bcb4c963f2ddae06a2efc7e9f3591312473c50c6685e1f298068316e66fe"
+
+[[package]]
+name = "lazycell"
+version = "1.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "830d08ce1d1d941e6b30645f1a0eb5643013d835ce3779a5fc208261dbe10f55"
+
+[[package]]
+name = "libc"
+version = "0.2.172"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d750af042f7ef4f724306de029d18836c26c1765a54a6a3f094cbd23a7267ffa"
+
+[[package]]
+name = "libloading"
+version = "0.8.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6a793df0d7afeac54f95b471d3af7f0d4fb975699f972341a4b76988d49cdf0c"
+dependencies = [
+ "cfg-if",
+ "windows-targets",
+]
+
+[[package]]
+name = "memchr"
+version = "2.7.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "78ca9ab1a0babb1e7d5695e3530886289c18cf2f87ec19a575a0abdce112e3a3"
+
+[[package]]
+name = "minimal-lexical"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "68354c5c6bd36d73ff3feceb05efa59b6acb7626617f4962be322a825e61f79a"
+
+[[package]]
+name = "nom"
+version = "7.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d273983c5a657a70a3e8f2a01329822f3b8c8172b73826411a55751e404a0a4a"
+dependencies = [
+ "memchr",
+ "minimal-lexical",
+]
+
+[[package]]
+name = "num-derive"
+version = "0.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ed3955f1a9c7c0c15e092f9c887db08b1fc683305fdf6eb6684f22555355e202"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "num-traits"
+version = "0.2.19"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "071dfc062690e90b734c0b2273ce72ad0ffa95f0c74596bc250dcfd960262841"
+dependencies = [
+ "autocfg",
+]
+
+[[package]]
+name = "proc-macro2"
+version = "1.0.95"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "02b3e5e68a3a1a02aad3ec490a98007cbc13c37cbe84a3cd7b8e406d76e7f778"
+dependencies = [
+ "unicode-ident",
+]
+
+[[package]]
+name = "quote"
+version = "1.0.40"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1885c039570dc00dcb4ff087a89e185fd56bae234ddc7f056a945bf36467248d"
+dependencies = [
+ "proc-macro2",
+]
+
+[[package]]
+name = "rb-sys"
+version = "0.9.115"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "99ca6726be0eca74687047fed7dcbc2d509571f3962e190c343ac1eb40e482b3"
+dependencies = [
+ "rb-sys-build",
+]
+
+[[package]]
+name = "rb-sys-build"
+version = "0.9.115"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9f2390cfc87b7513656656faad6567291e581542d3ec41dd0a2bf381896e0880"
+dependencies = [
+ "bindgen",
+ "lazy_static",
+ "proc-macro2",
+ "quote",
+ "regex",
+ "shell-words",
+ "syn",
+]
+
+[[package]]
+name = "rb-sys-env"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "08f8d2924cf136a1315e2b4c7460a39f62ef11ee5d522df9b2750fab55b868b6"
+
+[[package]]
+name = "regex"
+version = "1.11.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b544ef1b4eac5dc2db33ea63606ae9ffcfac26c1416a2806ae0bf5f56b201191"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-automata",
+ "regex-syntax",
+]
+
+[[package]]
+name = "regex-automata"
+version = "0.4.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "809e8dc61f6de73b46c85f4c96486310fe304c434cfa43669d7b40f711150908"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-syntax",
+]
+
+[[package]]
+name = "regex-syntax"
+version = "0.8.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2b15c43186be67a4fd63bee50d0303afffcef381492ebe2c5d87f324e1b8815c"
+
+[[package]]
+name = "runtime_tracing"
+version = "0.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "eafd7c2c0304ff7196100ad4b6d33ff61e27d7bdcc10efe75784364b86292451"
+dependencies = [
+ "num-derive",
+ "num-traits",
+ "serde",
+ "serde_json",
+ "serde_repr",
+]
+
+[[package]]
+name = "rustc-hash"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "08d43f7aa6b08d49f382cde6a7982047c3426db949b1424bc4b7ec9ae12c6ce2"
+
+[[package]]
+name = "ryu"
+version = "1.0.20"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "28d3b2b1366ec20994f1fd18c3c594f05c5dd4bc44d8bb0c1c632c8d6829481f"
+
+[[package]]
+name = "serde"
+version = "1.0.219"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5f0e2c6ed6606019b4e29e69dbaba95b11854410e5347d525002456dbbb786b6"
+dependencies = [
+ "serde_derive",
+]
+
+[[package]]
+name = "serde_derive"
+version = "1.0.219"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5b0276cf7f2c73365f7157c8123c21cd9a50fbbd844757af28ca1f5925fc2a00"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "serde_json"
+version = "1.0.140"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "20068b6e96dc6c9bd23e01df8827e6c7e1f2fddd43c21810382803c136b99373"
+dependencies = [
+ "itoa",
+ "memchr",
+ "ryu",
+ "serde",
+]
+
+[[package]]
+name = "serde_repr"
+version = "0.1.20"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "175ee3e80ae9982737ca543e96133087cbd9a485eecc3bc4de9c1a37b47ea59c"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "shell-words"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "24188a676b6ae68c3b2cb3a01be17fbf7240ce009799bb56d5b1409051e78fde"
+
+[[package]]
+name = "shlex"
+version = "1.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0fda2ff0d084019ba4d7c6f371c95d8fd75ce3524c3cb8fb653a3023f6323e64"
+
+[[package]]
+name = "syn"
+version = "2.0.101"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8ce2b7fc941b3a24138a0a7cf8e858bfc6a992e7978a068a5c760deb0ed43caf"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-ident",
+]
+
+[[package]]
+name = "unicode-ident"
+version = "1.0.18"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5a5f39404a5da50712a4c1eecf25e90dd62b613502b7e925fd4e4d19b5c96512"
+
+[[package]]
+name = "windows-targets"
+version = "0.53.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b1e4c7e8ceaaf9cb7d7507c974735728ab453b67ef8f18febdd7c11fe59dca8b"
+dependencies = [
+ "windows_aarch64_gnullvm",
+ "windows_aarch64_msvc",
+ "windows_i686_gnu",
+ "windows_i686_gnullvm",
+ "windows_i686_msvc",
+ "windows_x86_64_gnu",
+ "windows_x86_64_gnullvm",
+ "windows_x86_64_msvc",
+]
+
+[[package]]
+name = "windows_aarch64_gnullvm"
+version = "0.53.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "86b8d5f90ddd19cb4a147a5fa63ca848db3df085e25fee3cc10b39b6eebae764"
+
+[[package]]
+name = "windows_aarch64_msvc"
+version = "0.53.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c7651a1f62a11b8cbd5e0d42526e55f2c99886c77e007179efff86c2b137e66c"
+
+[[package]]
+name = "windows_i686_gnu"
+version = "0.53.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c1dc67659d35f387f5f6c479dc4e28f1d4bb90ddd1a5d3da2e5d97b42d6272c3"
+
+[[package]]
+name = "windows_i686_gnullvm"
+version = "0.53.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9ce6ccbdedbf6d6354471319e781c0dfef054c81fbc7cf83f338a4296c0cae11"
+
+[[package]]
+name = "windows_i686_msvc"
+version = "0.53.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "581fee95406bb13382d2f65cd4a908ca7b1e4c2f1917f143ba16efe98a589b5d"
+
+[[package]]
+name = "windows_x86_64_gnu"
+version = "0.53.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2e55b5ac9ea33f2fc1716d1742db15574fd6fc8dadc51caab1c16a3d3b4190ba"
+
+[[package]]
+name = "windows_x86_64_gnullvm"
+version = "0.53.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0a6e035dd0599267ce1ee132e51c27dd29437f63325753051e71dd9e42406c57"
+
+[[package]]
+name = "windows_x86_64_msvc"
+version = "0.53.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "271414315aff87387382ec3d271b52d7ae78726f5d44ac98b4f4030c91880486"
diff --git a/ext/native_tracer/Cargo.toml b/ext/native_tracer/Cargo.toml
new file mode 100644
index 0000000..937f7c4
--- /dev/null
+++ b/ext/native_tracer/Cargo.toml
@@ -0,0 +1,15 @@
+# Cargo.toml
+[package]
+name = "codetracer_ruby_recorder"
+description = "Native Ruby module for generating CodeTracer trace files"
+version = "0.1.0"
+edition = "2021"
+crate-type = ["cdylib"]
+build = "build.rs"
+
+[dependencies]
+rb-sys = "0.9"
+runtime_tracing = "0.10.0"
+
+[build-dependencies]
+rb-sys-env = "0.2"
diff --git a/ext/native_tracer/README.md b/ext/native_tracer/README.md
new file mode 100644
index 0000000..f44a8c8
--- /dev/null
+++ b/ext/native_tracer/README.md
@@ -0,0 +1,55 @@
+# codetracer_ruby_recorder
+
+This crate provides a minimal Ruby tracer implemented in Rust.
+It registers a Ruby VM event hook using `rb_add_event_hook2` and
+records basic information for each executed line.
+
+Recorded events are written using the [`runtime_tracing`](https://github.com/metacraft-labs/runtime_tracing) crate.
+
+## Building
+
+```
+cargo build --release
+```
+
+If you have `just` installed, run `just build-extension` from the project root.
+
+The produced shared library can be required from Ruby:
+
+```ruby
+require_relative 'target/release/libcodetracer_ruby_recorder'
+```
+
+Once loaded, the tracer starts writing a trace to `trace.json` or the
+path specified via the `CODETRACER_DB_TRACE_PATH` environment variable.
+
+## Publishing platform-specific gems
+
+This extension can be packaged as a Ruby gem so the compiled library is
+distributed for each target platform. The gemspec at the project root uses
+[`rb_sys`](https://github.com/oxidize-rb/rb-sys) to build the library.
+
+To publish prebuilt binaries:
+
+1. Install the development dependencies:
+
+   ```bash
+   bundle install
+   ```
+
+2. For each target triple, set `RB_SYS_CARGO_TARGET` and run the packaging task:
+
+   ```bash
+   RB_SYS_CARGO_TARGET=x86_64-unknown-linux-gnu rake cross_native_gem
+   ```
+
+   Replace the target triple with the platform you want to build for, e.g.
+   `aarch64-apple-darwin` or `x86_64-pc-windows-msvc`.
+
+3. Push the generated gem from the `pkg/` directory to RubyGems:
+
+   ```bash
+   gem push pkg/codetracer-ruby-recorder-0.1.0-x86_64-linux.gem
+   ```
+
+Repeat these steps for each platform to provide platform-specific gems.
diff --git a/ext/native_tracer/build.rs b/ext/native_tracer/build.rs
new file mode 100644
index 0000000..1c710e6
--- /dev/null
+++ b/ext/native_tracer/build.rs
@@ -0,0 +1,4 @@
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    rb_sys_env::activate()?;
+    Ok(())
+}
diff --git a/ext/native_tracer/extconf.rb b/ext/native_tracer/extconf.rb
new file mode 100644
index 0000000..118d35e
--- /dev/null
+++ b/ext/native_tracer/extconf.rb
@@ -0,0 +1,4 @@
+require 'mkmf'
+require 'rb_sys/mkmf'
+
+create_rust_makefile('codetracer_ruby_recorder')
diff --git a/ext/native_tracer/src/lib.rs b/ext/native_tracer/src/lib.rs
new file mode 100644
index 0000000..3d26cb9
--- /dev/null
+++ b/ext/native_tracer/src/lib.rs
@@ -0,0 +1,64 @@
+#![allow(clippy::missing_safety_doc)]
+
+use std::{ffi::CStr, mem::transmute, os::raw::c_char};
+
+use rb_sys::{
+    // frequently used public items
+    rb_add_event_hook2, rb_event_flag_t,
+    rb_event_hook_flag_t::RUBY_EVENT_HOOK_FLAG_RAW_ARG,
+    ID, VALUE, RUBY_EVENT_LINE,
+
+    // the raw-trace-API symbols live in the generated `bindings` module
+    bindings::{
+        rb_trace_arg_t,             // struct rb_trace_arg
+        rb_tracearg_event_flag,     // event kind helpers
+        rb_tracearg_lineno,
+        rb_tracearg_path,
+    },
+};
+
+/// Raw-argument callback (Ruby will call it when we set
+/// `RUBY_EVENT_HOOK_FLAG_RAW_ARG`).
+///
+/// C prototype:
+/// ```c
+/// void (*)(VALUE data, rb_trace_arg_t *arg);
+/// ```
+unsafe extern "C" fn event_hook_raw(_data: VALUE, arg: *mut rb_trace_arg_t) {
+    if arg.is_null() {
+        return;
+    }
+
+    let ev: rb_event_flag_t = rb_tracearg_event_flag(arg);
+    if (ev & RUBY_EVENT_LINE) == 0 {
+        return;
+    }
+
+    let path_ptr = rb_tracearg_path(arg) as *const c_char;
+    let line = rb_tracearg_lineno(arg) as u32;
+
+    if !path_ptr.is_null() {
+        if let Ok(path) = CStr::from_ptr(path_ptr).to_str() {
+            println!("Path: {path}, Line: {line}");
+        }
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Init_codetracer_ruby_recorder() {
+    unsafe {
+        // rb_add_event_hook2’s first parameter is a function pointer with the
+        // classic five-argument signature.  We cast our raw callback to that
+        // type via an intermediate variable so the sizes match.
+        let raw_cb: unsafe extern "C" fn(VALUE, *mut rb_trace_arg_t) = event_hook_raw;
+        let cb: unsafe extern "C" fn(rb_event_flag_t, VALUE, VALUE, ID, VALUE) =
+            transmute(raw_cb);
+
+        rb_add_event_hook2(
+            Some(cb),                 // callback (now cast)
+            RUBY_EVENT_LINE,          // which events
+            0,                        // user data
+            RUBY_EVENT_HOOK_FLAG_RAW_ARG,
+        );
+    }
+}
diff --git a/flake.nix b/flake.nix
index f160c6f..6a1e556 100644
--- a/flake.nix
+++ b/flake.nix
@@ -12,7 +12,18 @@
         let pkgs = import nixpkgs { inherit system; };
         in {
           default = pkgs.mkShell {
-            packages = with pkgs; [ ruby just git-lfs ];
+            packages = with pkgs; [
+              ruby
+
+              # The native extension is implemented in Rust
+              rustc
+              cargo
+              libiconv # required as a dependency when building the rb-sys Rust crate
+
+              # For build automation
+              just
+              git-lfs
+            ];
           };
         });
     };