marker-watch-mcp

marker-watch-mcp is an MCP server for one long-running command. It watches that command's output for a start and end marker, then saves the enclosed output as a numbered build result.

Use it when another tool already reruns your build or check command. This server does not watch files or restart processes.

Install

Node.js 20+ and pnpm are required.

pnpm install
pnpm build
pnpm link -g

Ensure pnpm's global bin directory is on your PATH, then configure your MCP client to run the linked command:

{
  "mcpServers": {
    "marker-watch": {
      "command": "marker-watch-mcp",
      "args": [
        "--cwd", "/absolute/path/to/project",
        "--start-marker", "@@build:start@@",
        "--end-marker", "@@build:end@@",
        "--",
        "your-watcher", "--", "your-check-command"
      ]
    }
  }
}

Everything after -- is the command to run, with its arguments unchanged. You can instead use --command and --args, or the corresponding MARKER_WATCH_MCP_* environment variables. --log-file /tmp/marker-watch.log keeps a raw output log.

How it works

The command must stay running and write a start marker followed by an end marker for each run. Markers match literal text in complete output lines after terminal color codes are removed. The saved result keeps the original output.

The server keeps the latest 20 completed results. It exposes these MCP tools:

• get_build_status — current process and build state.
• get_build — a saved result; omit version for the latest.
• await_build — wait for the next result after a version.
• start_build_wait and get_build_wait — start and poll a non-blocking wait.
• debug_get_live_output — recent raw output for diagnosing a stuck run.

Typical use

get_build_status()                -> latestCompletedVersion: 41
edit files                        -> your watcher runs the check
await_build({ afterVersion: 41 }) -> version 42 and its output

For a long check, call start_build_wait({ afterVersion: 41 }) and poll the returned ID with get_build_wait.