FolderBridge MCP

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A safer, local-first bridge between AI clients and a small set of folders you explicitly choose.

FolderBridge MCP is a zero-dependency Python MCP server plus a desktop launcher. It lets ChatGPT on the web—or any client that supports local stdio MCP—inspect and carefully edit a bounded local workspace. It deliberately avoids a public HTTP server, arbitrary shell access, telemetry, and silent background services.

0.5.1 highlights

• Browser-authorized GitHub publishing: the new bundled git-publisher extension can open GitHub authorization through Git Credential Manager, keep OAuth credentials in Windows Credential Manager, commit only an explicit file allowlist, and push only the current branch to the existing GitHub HTTPS origin. No token/PAT/password field is exposed to the model.

• Git publication remains constrained: Publisher rejects pre-existing staged changes, credential/key-like files, content-transforming Git attributes and unsafe repository-local Git settings; it never runs git add ., never accepts an arbitrary remote/ref, disables hooks/signing for its bounded commit, and never force-pushes.

• Native Microsoft Office visual pipeline: the bundled office extension can render .pptx, .docx, and .xlsx with locally installed Microsoft Office. PowerPoint exports slides directly to PNG; Word/Excel use their native fixed-format layout engines and the Windows PDF renderer to produce page PNGs.

• Word structure reading without launching Word: inspect_docx exposes paragraphs, styles/numbering, tables, sections/page setup, headers/footers, media, hyperlinks, footnotes/endnotes and comments from OOXML.

• Excel structure/formula reading without launching Excel: inspect_xlsx exposes sheets, bounded cell ranges, formulas plus cached values, merged ranges, hidden rows/columns, defined names, calculation settings and external-link parts.

• Audit-ready output: native rendering can write a deterministic PNG directory plus sibling ZIP and returns SHA-256/size metadata for both the Office source and generated outputs; the existing image_open tool can then inspect each page or ZIP member visually.

• Office automation is constrained: only workspace-relative non-link paths are accepted; macro-enabled formats are excluded; Office automation macros are force-disabled; files open read-only; Excel link updates are disabled; the bundled PowerShell script is fixed and never accepts arbitrary commands.

• Existing 0.4.x safety/UI improvements remain: high-DPI scrolling, ComfyUI managed-service diagnostics, stable extension gateway, bounded global capabilities, and single-file Windows delivery are unchanged.

See CHANGELOG.md for the full release history and Extension ABI v1 for managed-service and plugin boundaries.

Related MCP server: mcp-readonly-code-server

Why FolderBridge?

• Independent folder boundaries: one connection can contain up to eight canonical workspaces; every multi-workspace tool call selects a workspace_id instead of merging roots.

• Read-only by default: switch to read/write explicitly in the launcher.

• Conflict-safe edits: existing files require the SHA-256 returned by the last read; stale edits fail instead of overwriting newer work.

• No arbitrary shell: optional tasks are named, locally reviewed, and approved by exact config hash.

• No public listener: the MCP server uses stdio only.

• No telemetry: FolderBridge itself makes no network requests.

• Secret-aware launcher: the OpenAI Runtime API key stays in memory and is removed before the local MCP process can use it.

• Beginner-friendly desktop UI: an add/remove folder list, global access mode, Tunnel setup, diagnostics, start/stop, process monitoring, and redacted logs live in one window.

• Windows scaling support: fonts and window sizing follow the current display DPI and refresh when moving between monitors with different scale factors.

Quick start

Requirements depend on how you use FolderBridge:

• Standalone Windows EXE: no separate Python or Node.js installation is required; Windows is the tested double-click launcher environment.

• Run/develop from source: Python 3.11 or newer is required; Python 3.11 x64 is the recommended Windows build baseline.

• Project capabilities: install only the toolchain required by the workspace itself (for example Node.js LTS for a Node/npm project's test/build scripts). Enabling a capability does not install that toolchain.

• Git is optional. Bounded status/diff views use Git when available; the Git Publisher extension additionally requires Git for Windows with Git Credential Manager for browser-authorized GitHub commits/pushes.

Windows executable — recommended

Download the single FolderBridge.exe from the latest GitHub release Assets, or download the EXE directly. The binary does not appear in the repository's source-file list. FolderBridge.exe is the complete FolderBridge application and already contains its Python runtime, so normal EXE users do not install Python or Node.js. The adjacent FolderBridge.exe.sha256 file is optional and exists only for integrity verification.

The one-file executable deliberately does not rebundle OpenAI's independently released tunnel-client; download the official client separately from OpenAI's release and select tunnel-client.exe in the launcher only when using ChatGPT on the web.

Run from source

Clone the repository and start the GUI:

git clone https://github.com/MoonTzai/folderbridge-mcp.git
cd folderbridge-mcp
python .\folderbridge_launcher.py gui

Add the workspaces you need, keep Read only selected for the first run, and use the status panel to finish setup. Launcher preferences are stored outside the repository; the Runtime API key is never saved. A legacy single-workspace setting is migrated into the first list entry automatically.

folderbridge_gui.pyw is kept as a source-only convenience for Python installations whose .pyw association points to an interpreter with Tkinter. The standalone FolderBridge.exe is the supported double-click entry point.

Optional development and project toolchains

These are not prerequisites for normal FolderBridge.exe use:

• For source development or rebuilding the Windows EXE, install Python 3.11 x64 from the official Python Windows downloads and verify python --version. The packaging flow uses an isolated .build-venv and requirements-build.txt.

• Install Node.js LTS from the official Node.js downloads only when a target Node/npm workspace needs node/npm for its own test or build commands; verify with node --version and npm --version.

• Other projects may require their own runtimes or compilers. FolderBridge capabilities provide authorization and bounded discovery/execution, not dependency installation.

Connect ChatGPT on the web

ChatGPT cannot connect directly to a local stdio process. FolderBridge uses OpenAI's official Secure MCP Tunnel for this path. You need:

• a tunnel_id from OpenAI Platform Tunnel settings;

• a key for tunnel-client from the same organization's Runtime API Keys;

• the official tunnel-client;

• ChatGPT developer-mode access appropriate for your account or workspace.

Click 连接设置向导 (Connection setup guide) in the launcher's upper-right corner for the same steps and shortcuts below, including the optional Python/Node appendix.

1. Download the official Windows x64 client

1. Open the latest openai/tunnel-client release and expand Assets.

2. Download the complete archive named tunnel-client-v<version>-windows-amd64.zip. In release filenames, amd64 means Windows x64 and is correct for most Intel/AMD PCs.

3. Optionally download SHA256SUMS.txt for verification. Do not choose tunnel-client-runtime-*, windows-arm64, all.zip, source-code archives, or license files; a Runtime archive cannot replace the complete client.

4. Extract the entire ZIP to a stable folder; there is no installer, and you should not run it from inside the archive. The guide can create and open %LOCALAPPDATA%\FolderBridge\bin as a recommended location.

5. Return to FolderBridge, click 选择已解压的 EXE, and select only the file named exactly tunnel-client.exe.

2. Create the Platform Tunnel

Open OpenAI Platform Tunnel settings, click Create tunnel, and use these current choices:

After creation, copy the Tunnel ID beginning with tunnel_. Running and selecting it requires Tunnels Read + Use; creating or editing it also requires Manage. Associate only the organizations and ChatGPT workspaces that need access to this local workspace.

Create the key for tunnel-client under the same Platform organization's Runtime API Keys; its creator needs Tunnels Read + Use. Paste it only into FolderBridge, where it remains in process memory. Do not use an Admin API key, and do not put the Runtime key into the ChatGPT app's Authentication field.

3. Start FolderBridge

1. Add one or more explicit workspace folders (up to eight) and keep Read only (recommended) for the first run. The global access mode applies to every listed folder.

2. Select tunnel-client.exe from the complete archive, never a tunnel-client-runtime-* component; the default folderbridge profile is suitable.

3. Enter the same Tunnel ID and Runtime API key. Optionally enable the global capabilities you want once; leave per-workspace advanced named tasks disabled unless you need a custom command.

4. Click Start connection. The launcher runs the official init, doctor, and run flow. Continue only after the top status reads 运行中 (Running). When changing the folder or access mode later, click 应用配置 (Apply configuration) again; the launcher updates the same profile that it manages.

4. Create the ChatGPT developer-mode app

Open ChatGPT Plugins, click +, and use these critical choices:

Invoke the app in a ChatGPT conversation

1. Keep the FolderBridge status at 运行中 (Running), then start a new ChatGPT conversation.

2. Select the + beside the composer, open More, and choose the FolderBridge app that you just created.

3. Send a task such as: “First use FolderBridge server_info to list the available workspaces, then read the root of the workspace I name.” Review the workspace_id and target file in any tool confirmation before approving it.

This entry point follows OpenAI's official connect and test guidance. The launcher's connection guide includes the same steps and a one-click copyable example prompt.

Keep the launcher running while ChatGPT uses the workspace. Closing it stops the Tunnel process. Account-level developer-mode and app installation confirmations remain in ChatGPT; FolderBridge does not automate your browser session or security settings.

No browser extension is required. FolderBridge intentionally does not silently download or execute network-delivered binaries.

Connect another local MCP client

Yes. FolderBridge's compatibility seam is its standard MCP stdio server. The ChatGPT Tunnel is only a bridge for a web client that cannot launch a local process. The MCP stdio transport likewise specifies that the client launches the server subprocess and exchanges JSON-RPC over standard input/output. MCP stdio specification

Client requirements

• It can configure a local command + args pair and keep the subprocess running.

• It supports MCP over stdio, keeping stdout reserved for protocol messages.

• It can discover and call MCP tools (initialize, tools/list, and tools/call, or the modern 2026-07-28 discovery flow).

• It closes stdin or terminates the subprocess when the session ends.

• Prefer a client with tool approval UX, but do not treat its confirmation dialog as the only security boundary.

FolderBridge currently handles the 2024-11-05, 2025-03-26, 2025-06-18, 2025-11-25, and 2026-07-28 protocol paths. It returns standard tool schemas, text content, and structuredContent; whether a confirmation prompt appears is client-specific. MCP Tools specification

Shortest local setup

1. Add one or more workspaces in FolderBridge and keep Read only (recommended).

2. Open page 5 of 连接设置向导 and copy JSON, TOML, or the complete stdio command.

3. Paste it into the client's MCP Servers settings; follow that client's documentation for its exact field names.

4. Restart or refresh the client and verify that server_info and workspace appear.

A direct stdio connection needs no tunnel-client, Tunnel ID, Runtime API key, or running FolderBridge GUI. The client starts this command when needed:

FolderBridge.exe serve --workspace C:\path\to\repo --read-only

Repeat --workspace to add folders while keeping each root independent:

FolderBridge.exe serve --workspace C:\work\frontend --workspace C:\work\backend --read-only

Generate ready-to-paste configurations from source:

python .\folderbridge_launcher.py client-config --workspace C:\path\to\repo --format json --read-only
python .\folderbridge_launcher.py client-config --workspace C:\path\to\repo --format toml --read-only
python .\folderbridge_launcher.py client-config --workspace C:\path\to\repo --format tunnel --read-only

The JSON output follows the common mcpServers convention used by many desktop clients:

{
  "mcpServers": {
    "folderbridge": {
      "command": "C:\\Tools\\FolderBridge.exe",
      "args": ["serve", "--workspace", "C:\\work\\frontend", "--workspace", "C:\\work\\backend", "--read-only"]
    }
  }
}

See the client compatibility research for protocol versions, process lifecycle, cwd/env, approval boundaries, and remote bridging details.

Tools and editing workflow

The built-in server tools do not depend on per-workspace task configuration:

• server_info: reports each available workspace name, stable workspace_id, built-in/global capabilities, and safety boundary;

• workspace: lists, reads, searches, and shows bounded Git status/diff output inside the selected workspace_id;

• file_info: returns bounded metadata and SHA-256 for binary files;

• pptx_inspect: inspects PPTX text, OOXML diagram relationships, and SmartArt data without executing Office content;

• image_open: returns bounded PNG/JPEG/GIF/WebP image content to the MCP client, including exact image members inside ZIP files;

• extension: the stable list / info / run gateway for hot-loaded extensions; installing more plugins does not add MCP tool names;

• edit_file: in read/write mode, creates or exactly edits a UTF-8 file inside the selected workspace.

With one workspace, existing clients may continue omitting workspace_id. With multiple workspaces, workspace-scoped tools require a workspace_id returned by server_info; missing or unknown IDs are rejected. Duplicate roots, parent/child overlaps, and lists beyond eight entries are rejected before startup.

A safe edit loop is:

1. list or search for a file;

2. read it and retain the returned SHA-256;

3. submit an exact replacement with that hash;

4. inspect the Git diff.

The server cannot delete or move files. Absolute paths, .., symlinks, junctions/reparse points, VCS internals, common dependency/build folders, and credential-like names are denied.

Global pre-authorized capabilities

The launcher can authorize common capabilities once for all current and future workspaces: test, build, package-windows, package-android, and git-push. These permissions live in the launcher settings rather than .folderbridge.json, so a workspace can gain a supported build script months after it was added and FolderBridge will detect it at call time. The launcher also provides Select all and Clear controls for this group.

git-push remains a low-level push-only capability constrained to a GitHub HTTPS origin, the current branch, no force push, and no repository-local credential helper / push-target rewrite configuration. For browser authorization plus explicit-file commit + push, use the bundled Git Publisher extension instead. Build/package capabilities may execute local project code, so enable only the global capabilities you want.

For direct stdio clients, repeat --capability <name> on the serve or client-config command. The Windows launcher exposes the same choices as persistent checkboxes.

Extensions

FolderBridge Extension ABI v1 is the preferred way to add future global integrations such as ComfyUI, FFmpeg, Blender, Ollama, ADB, or other local tools without changing the MCP tool catalog. The Windows launcher has a default-collapsed Extensions sidebar that hot-scans the user extension directory, shows installed/approved/loaded state, and lets you approve or disable plugins while the Tunnel remains connected.

Each extension is a directory containing at least folderbridge-extension.json and plugin.py. External plugins are approved against the exact SHA-256 of the complete plugin directory plus the declared permission list; changing any file or permission makes the approval stale. Extensions execute in a separate subprocess with a cleaned environment, bounded protocol I/O, and a declared timeout. This isolates crashes and protocol pollution, but it is not an OS security sandbox: use a VM/container for untrusted plugin code.

Workspace-specific adaptation should use workspace_adapter.mode=dynamic with detect.any_of / detect.all_of. FolderBridge re-evaluates those patterns at call time, so extensions do not need to inject .folderbridge.json tasks when installed and can become applicable after a project changes later. Persistent plugin state should use the provided profile state directory rather than polluting repositories.

ComfyUI is the first bundled extension. Its status action checks the fixed loopback endpoint 127.0.0.1:8188; workflow execution requires one-time approval in the Extensions sidebar. In FolderBridge 0.4.1 the Windows launcher can also manage the local ComfyUI process itself: choose a supported Portable root (python_embeded\\python.exe + ComfyUI\\main.py) or source root (main.py + .venv\\Scripts\\python.exe / venv\\Scripts\\python.exe) once, and the launcher can auto-start it with explicit Python/main.py arguments, shell=False, and fixed 127.0.0.1:8188 binding. If that endpoint is already online before FolderBridge starts it, the service is marked external and reused rather than duplicated.

Managed-service ownership is intentionally stricter than Extension permissions. FolderBridge stores only install_root and auto_start, never a PID or arbitrary command. Only the in-memory Popen handle created by the current launcher run is considered owned and stoppable. FolderBridge never runs a user-selected BAT/CMD for ComfyUI and never looks up or kills an unknown process merely because it occupies port 8188. On exit it stops owned managed services before Tunnel/MCP; external ComfyUI remains running.

On Windows, the launcher requests Per-Monitor DPI V2 awareness and also polls the current window DPI as a lightweight fallback. Fixed GUI metrics are recalculated from their original logical sizes (dpi / 96) only when DPI actually changes, so moving 96 → 144 → 96 DPI does not accumulate scale drift.

ABI v1 plugins should use FolderBridge-packaged modules and the Python standard library rather than assuming arbitrary pip dependencies inside the one-file EXE. Extra software should normally be reached through a precise loopback API or a declared process.execute:<basename> dependency. Run FolderBridge.exe extensions --json to inspect what the packaged executable can discover. The connection guide appendix contains the complete format plus a one-click LLM plugin-development prompt that tells the model to request/upload missing API docs, scripts, workflows, sample files, or project structure instead of guessing. See Extension ABI v1.

Optional per-workspace named tasks

Arbitrary command text is never accepted through MCP. For unusual repository-specific commands that are not covered by global capabilities, create and review a local task policy:

python .\folderbridge_launcher.py init --workspace C:\path\to\repo
# Review C:\path\to\repo\.folderbridge.json
python .\folderbridge_launcher.py approve --workspace C:\path\to\repo

Then enable approved tasks in the launcher or add --allow-tasks to the generated server command. Enabling this switch does not require every configured workspace to contain .folderbridge.json: no-config workspaces, approved-task workspaces, extension-only workspaces, and workspaces whose config has not yet been approved can coexist in one connection. Approval is checked when that workspace's named task is actually invoked. The model can select only a task name; it cannot provide a command, arguments, environment variables, or working directory.

Security model

FolderBridge treats MCP requests, repository text, and tool output as untrusted data. Enforcement lives in the tool implementation rather than MCP annotations alone. The main controls are:

• canonical path confinement and link rejection per workspace, with overlapping roots denied;

• bounded UTF-8 reads, searches, Git output, subprocess output, and protocol messages;

• atomic writes with a current-content hash precondition;

• protected local policy files;

• shell=False, fixed argument arrays, clean task environments, and timeouts;

• extension manifests reject unknown/overbroad permission names, extension approvals bind exact code hashes and permissions, and plugin execution is moved out of the MCP process;

• no inbound network listener and no FolderBridge telemetry.

Read the complete security model and the upstream design research. To report a vulnerability, follow SECURITY.md.

Development

There are no third-party runtime dependencies.

python -m unittest discover -s tests -v

See CONTRIBUTING.md before opening a pull request.

Build the Windows executable

Builds use a pinned, build-time-only PyInstaller dependency. The released EXE uses the console bootloader with hide-console=hide-early: double-clicking opens only the GUI, while the same executable retains stdio when Tunnel starts its serve subcommand.

python -m venv .build-venv
.\.build-venv\Scripts\python.exe -m pip install -r requirements-build.txt
.\scripts\build_windows.ps1 -Python .\.build-venv\Scripts\python.exe

Artifacts and a SHA-256 file are written to release\windows-x64.

License

Licensed under the Apache License 2.0.

FolderBridge MCP is an independent open-source project. It is not affiliated with, endorsed by, or sponsored by OpenAI. ChatGPT, OpenAI, MCP, and other product names belong to their respective owners.