OpenReaper

OpenReaper is an open-source MCP bridge and agent kernel for REAPER, developed by Streetlight Studio. The internal code name is still Streetlight in many package names, logs, and paths; the public project name is OpenReaper. OpenReaper is independent and unofficial; it is not affiliated with Cockos or the REAPER project.

The first goal is deliberately small: let any MCP-capable agent control REAPER through safe, typed, testable, undoable operations. Game audio is the first official workflow pack, not the limit of the system.

What It Does

OpenReaper exposes a compact tool surface for agents:

• inspect the current REAPER project state
• import and arrange audio
• create variations for selected items
• apply common game-audio edits such as pitch, rate, reverse, trim, fades, regions, and renders
• run tested Lua templates instead of asking an LLM to invent ReaScript from scratch
• expose capabilities with schemas, risk levels, logs, and verification

The intended first workflow:

Select or provide a source sound, ask an agent for impact/weapon/UI/foley variations, then let OpenReaper create edited items, regions, and rendered WAV files in REAPER.

Why This Shape

LLMs are useful at planning sound design work, but unreliable when they freely write REAPER Lua. OpenReaper keeps the creative planning in the agent and moves DAW manipulation into tested templates with explicit schemas.

That gives the project three useful properties:

• agent-neutral: works with Codex, Claude Code, Cursor, or any MCP client
• REAPER-native: uses ReaScript and the user's local REAPER installation
• extensible: new workflows can be added as templates and recipes without rebuilding the whole app

How To Run The Impact-Variations Demo

This is the v0.1 acceptance demo: from one selected media item, OpenReaper produces 8 named variations on a new track, wraps each in a region, and renders them to 8 WAV files.

Prerequisites

Before the first run, confirm each of these — a miss here is the usual cause of a demo that fails partway through with a typed error.

First-time install on this Mac: double-click install.command, or run npm install && npm run build && npm run setup from the repo root. Then register the generated launcher in REAPER (Actions → Show action list → ReaScript: Load... → ~/Library/Application Support/REAPER/Scripts/Streetlight/start_bridge.lua) and copy the snippet from setup-out/<your-client>.* into your MCP client config. The launcher path still says Streetlight because that is the v0.1 internal kernel name and compatibility path. Windows has install.cmd / install.ps1 as an experimental convenience path, but v0.1 live verification is macOS. Full details in docs/INSTALL.md; cross-Mac reproducer in docs/CROSS_MAC_SMOKE.md.

1. REAPER 7.x is running with the OpenReaper / Streetlight bridge loaded. The console (View → Show console) shows bridge ready (generation N) — templates: …. See docs/INSTALL.md.
2. "Render in background" is ON. REAPER → Preferences → Audio → Rendering → "Render in background (does not apply to queued renders)" checked. Required for render_region — see INSTALL.md § Requirements.
3. Pick a FRESH or empty output directory (e.g. ~/Desktop/streetlight-demo/). Must be absolute (Lua's io.open does not expand ~ — use the resolved path, e.g. /Users/you/Desktop/streetlight-demo/). The directory must exist and be writable; the demo refuses to overwrite existing files (OUTPUT_FILE_EXISTS).
4. Pick a FRESH project, or at minimum confirm no existing regions are named var_01 .. var_08. The demo creates regions with those names; a collision surfaces REGION_NAME_TAKEN and stops the run.
5. Select exactly one media item in REAPER — this is the source the variations are derived from. The recipe binds that item's GUID up front and reuses it for every duplicate; the agent is instructed to abort before any mutating call if the initial selection count is not exactly 1.
6. MCP server is registered with your agent client (Codex / Claude Code). ping should round-trip in under a second.

The Prompt

In your MCP-capable agent, send:

Use OpenReaper to make 8 impact variations from the selected item.
First call list_recipes and follow impact_variations step by step,
rendering all 8 WAVs to /absolute/path/to/your/output_dir.

Substitute the absolute path you confirmed in prerequisite #3.

What Should Happen

• one new track named Streetlight - Impact Variations appears
• 8 items duplicated from the source land on that track (var_01..var_08), each with the recipe's pitch/rate/fade applied
• 8 regions wrap those items
• 8 WAV files appear in your output directory, named var_01.wav .. var_08.wav (24-bit PCM, project sample rate, stereo)
• the output directory contains exactly those 8 WAVs and nothing else — in particular, no <region>.wav.RPP / <region>.wav.RPP-bak project-copy sidecars. v0.1 enforces this WAV-only artifact contract through guarded cleanup, not REAPER-config suppression: before each render render_region refuses to start if a .wav, .wav.RPP, or .wav.RPP-bak already exists at the target (typed OUTPUT_FILE_EXISTS), and after a successful render it deletes any sidecar REAPER auto-wrote alongside the WAV. (Config-var suppression was ruled out in Step 7 — reaper.set_config_var_string is absent on stock REAPER 7.71/macOS-arm64; see PROGRESS.md for the post-mortem.) A .RPP or .RPP-bak sidecar showing up in the output dir means the guarded-cleanup contract regressed; report it.
• the agent reports back the 8 file paths and the per-variation parameters

Total wall-clock on typical hardware: under 3 minutes.

Cmd+Z walks back the project changes one template at a time (about 30 steps to fully revert items, tracks, and regions). The rendered WAV files on disk are not part of the project state and are not removed by undo.

If It Stops Partway

Recoverable errors the agent will see and can usually retry past:

• OUTPUT_DIR_MISSING / OUTPUT_DIR_NOT_WRITABLE — fix prerequisite #3
• OUTPUT_FILE_EXISTS — choose a fresh output dir or delete old var_*.wav
• REGION_NAME_TAKEN — fresh project, or delete old var_01..var_08 regions
• BRIDGE_NOT_RUNNING on render_region — usually means "Render in background" is OFF; see prerequisite #2

list_recipes is a doc — OpenReaper does NOT execute the recipe for you. The agent reads the YAML and issues one call_template per step. If you'd prefer to drive the loop yourself, the templates and parameters are all listed in recipes/impact_variations.yaml.

Architecture

MCP-capable agent
  Codex / Claude Code / Cursor / future desktop UI
        |
        v
streetlight-mcp
  typed tools and schemas
        |
        v
streetlight-core
  operation validation, templates, recipes
        |
        v
streetlight-bridge.lua
  runs inside REAPER

See docs/ARCHITECTURE.md for the full v0.1 specification.

See docs/KERNEL_DESIGN.md for the longer foundation design and analogies behind the kernel model.

MVP

The MVP is one polished loop, not a feature catalog:

1. connect an MCP agent to a running REAPER session
2. read selected items and project context
3. create 6-10 usable variations from one source sound
4. place variations on tracks with clear names
5. create regions
6. render WAV files to an output folder
7. return a structured report of what changed

See docs/MVP.md.

For the concrete file-by-file build plan, see docs/IMPLEMENTATION_PLAN.md.

For the render mechanics that the MVP demo lives or dies on, see docs/RENDER_NOTES.md.

Roadmap

See docs/ROADMAP.md for what should wait until after the first reliable workflow.

Internal planning, rough strategy, and private notes should live outside this public repository.

Non-Goals For v0.1

• standalone desktop UI
• semantic sound library search
• Wwise integration
• ElevenLabs or other generation services
• automatic SWS/ReaPack installation
• universal DAW support
• unrestricted remote code execution

License

TBD before first public release.