Sigil MCP Bridge

Connects Codex and other Model Context Protocol clients to the EPUB currently open in Sigil.

The recommended external-editor mode runs in the background, keeps Sigil usable and edits only existing textual resources. Reads return a SHA-256 hash; writes require that hash and are rejected if the file changed in the meantime.

Requirements

• Windows 10 or later for the background external-editor launcher

• Sigil 2.x

• Python 3.8 or later for the MCP server (Sigil already bundles Python)

• Node.js 18 or later only when installing the MCP server from npm

The modal BookContainer plugin is also included and supports the platforms supported by Sigil, but it blocks the editor while its window is open.

Related MCP server: mcp-fstools

Install the non-modal Sigil bridge

1. Download Sigil-MCP-Bridge_v0.2.0.zip from the GitHub release and extract it to a permanent directory.

2. In Sigil, open Preferences > General Settings > Preferred external XHTML editor and select SigilMCPExternal.exe.

3. Open an EPUB and press F2 once. The bridge starts invisibly on http://127.0.0.1:8765.

Opening the external editor in another EPUB replaces the previous bridge instance, so only the most recently activated book is exposed. If Sigil uses a portable installation and Python is not found automatically, set SIGIL_PYTHON to Sigil's python3.exe.

Configure an MCP client

npm

[mcp_servers.sigil]
command = "npx"
args = ["-y", "sigil-mcp-bridge"]

[mcp_servers.sigil.env]
SIGIL_BRIDGE_URL = "http://127.0.0.1:8765"

Python directly

[mcp_servers.sigil]
command = "python3"
args = ["/absolute/path/to/sigil-mcp-bridge/mcp_server/sigil_mcp.py"]

[mcp_servers.sigil.env]
SIGIL_BRIDGE_URL = "http://127.0.0.1:8765"

For a Codex process running in WSL, use Sigil's Windows python3.exe as the command if WSL cannot reach the Windows loopback address.

Tools

• sigil_health

• sigil_book_info

• sigil_list_files

• sigil_selected_files

• sigil_read_file

• sigil_search

• sigil_write_file

The external mode does not add or remove manifest entries. Use the modal SigilMCPBridge plugin for future structural operations. Avoid editing the same XHTML simultaneously in the agent and Sigil's Code View.

Optional local token

The service binds only to 127.0.0.1 and rejects browser-originated requests. To also require a bearer token, set the same SIGIL_BRIDGE_TOKEN value in the environment that launches Sigil and in the MCP server configuration.

Modal plugin

Install SigilMCPBridge_v0.2.0.zip through Plugins > Manage Plugins. This mode uses Sigil's BookContainer API and intentionally keeps a plugin window open while active.

Build and test

Compile the Windows launcher with Windows PowerShell:

.\build.ps1

Run the dependency-free integration tests:

python test_bridge.py
python test_external_bridge.py

Create and inspect the npm package:

npm pack
npm publish --dry-run

Validated with Sigil 2.6.2, Python 3.13.2, Node.js 20 and PySide6 6.8.2.1.

License

MIT © 2026 Studio Agartha.