What is StringTheory? The Open-Source Rocksmith-Style Guitar Game, Explained

July 3, 2026by OpenFret Team

StringTheory is a free, open-source guitar and bass game that listens to your real instrument and scores what you play in real time. You load a song, pick a part, plug in, and a note highway scrolls while the game detects your single notes and chords and grades them live. It's built in Unity, licensed GPL-3.0, and lives on GitHub, where you can grab a prebuilt release instead of compiling it yourself. If Rocksmith walked away from its own idea, this is the community walking it back.

What it plays

The format support is the headline. StringTheory loads Rocksmith .psarc files, which means the enormous library of CDLC (custom downloadable content) built for Rocksmith 2014 works here: drop the files in the songs folder, refresh, and they import. It also reads Guitar Pro files (.gp, .gp3, .gp4, .gp5, .gpx), MusicXML, and Clone Hero-style charts, so you're not locked to the Rocksmith ecosystem. Songs with multiple arrangements let you switch between lead, rhythm, and bass, and CDLC with difficulty levels lets you change difficulty mid-game.

The practice modes

This is where it beats the game it's modeled on. Loop Mode repeats any section until it's clean, with savable bookmarks. Note By Note pauses on each note or chord and waits until you play it correctly before moving on, which is genuinely useful for hard passages. Hero Mode adds hearts and failure states when you want pressure instead of practice. There's speed control for slowing parts down and building back up, and scores save per song and per arrangement so you can chase your own runs.

Beyond the highway, there's a built-in Tone Lab, a pedalboard editor where you chain pedals, tweak parameters, manage presets, and set input latency without leaving the game. A separate arcade mode does Clone Hero-style play with keyboard, gamepad, guitar controller, or MIDI input, including local two-player. The developer posts updates on r/StringTheoryGame.

The CDLC gray zone

Now the uncomfortable part. The .psarc format belongs to Rocksmith, and most CDLC is charted from copyrighted songs without a license. Ubisoft has already shown it will act against projects in this space: in 2026 it DMCA'd Slopsmith and GitHub pulled the project and its forks overnight. StringTheory is arguably in a better position because psarc is one of four formats it reads rather than its foundation, and Guitar Pro and MusicXML are open. But if your entire library is CDLC, you're building on files that can vanish, and the project's history could repeat Slopsmith's. Worth knowing before you invest hours.

StringTheory vs fee[dB]ack vs Guitar Quest

The three open-ish options divide cleanly. StringTheory is the closest thing to actual Rocksmith: same file format, same play-a-song loop, plus better practice tools. fee[dB]ack, the renamed Slopsmith, dropped CDLC after the takedown and moved to its own open .feedpak format, and it covers bass, drums, and keys as well. Both are free desktop installs, and both assume you already know what to practice.

Guitar Quest is ours, and it's a different animal: not a song player but a guided RPG that teaches the fretboard, scales, and theory through play, in the browser, with all-original music. It costs $30 once rather than a subscription. Song players make you better at songs you already chose; a curriculum decides what you should work on next. Plenty of players end up wanting one of each.

Should you try it?

If you liked Rocksmith, own a desktop, and don't mind a little setup, yes. It's free, it's improving fast, and the note-by-note and loop modes are better practice tools than Ubisoft ever shipped. Go in knowing the CDLC risk, keep backups of your library, and if you also want something that tells you what to learn next, the Guitar Quest demo runs free in the browser alongside it.