sigmap MCP over HTTP (Podman)

An extremely lightweight Podman/OCI image that hosts the sigmap MCP server as a remote Streamable HTTP endpoint.

Why a bridge is needed

sigmap's MCP server speaks stdio only (sigmap --mcp) — its own docs note "the MCP server uses stdio, not a network port." To make it reachable over the network we wrap it with supergateway, which spawns the stdio server and re-exposes it over MCP Streamable HTTP:

MCP client ──HTTP──▶ supergateway ──stdio──▶ sigmap --mcp

Everything runs on a single Node.js runtime (Alpine base), so the image stays small and dependency-free beyond these two npm packages.

Related MCP server: MCP HTTP Proxy

Files

Build

Built as a single squashed layer (docker format is required for the baked-in HEALTHCHECK to be honored):

podman build --format docker --squash-all -t sigmap-mcp:latest .

Run

Bind-mount the repository you want sigmap to index at /workspace (read-write — sigmap stores its index/context files there):

podman run -d --name sigmap-mcp \
  --network=host \
  --userns=keep-id \
  -v /path/to/your/repo:/workspace \
  --restart unless-stopped \
  sigmap-mcp:latest

The MCP endpoint is then at http://localhost:8765/mcp, with a liveness probe at http://localhost:8765/healthz (returns ok). On startup the container builds an initial index of the mounted repo so tools return real data immediately (disable with -e AUTO_INDEX=false).

It also starts without a mount — tools just report "no context":

podman run --rm --network=host --name sigmap-mcp sigmap-mcp:latest

Port 8765 is the default because some Cursor team/enterprise MCP policies allowlist that local port. Override with -e PORT=... if you need a different one.

File access & permissions (rootless podman)

--userns=keep-id maps your host user into the container so bind-mounted files are readable and writable by sigmap. On this host (uid/gid 1000, matching the image's node user) files map cleanly and generated index files come back owned by you. If your host uid isn't 1000, force the mapping onto the node user with --userns=keep-id:uid=1000,gid=1000. Rootful podman doesn't need keep-id.

Networking notes

• Rootless without a network helper: if podman run -p ... fails with could not find slirp4netns (and pasta isn't installed either), run with the host network instead — the server binds directly to the host's port:

  podman run --rm --network=host --name sigmap-mcp sigmap-mcp:latest

• Behind an HTTP proxy: if http_proxy/https_proxy are set on the host, local curl tests may be hijacked by the proxy. Bypass it with --noproxy '*' (see the test below). The container's own healthcheck already avoids the proxy.

Configuration (env vars)

Example:

podman run -d --network=host -e LOG_LEVEL=debug -e AUTO_INDEX=false \
  -v "$PWD":/workspace --userns=keep-id --name sigmap-mcp sigmap-mcp:latest

Quick test

Initialize an MCP session (add --noproxy '*' if you are behind an HTTP proxy):

curl -sS --noproxy '*' http://127.0.0.1:8765/mcp \
  -H 'Content-Type: application/json' \
  -H 'Accept: application/json, text/event-stream' \
  -d '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"curl","version":"0"}}}'

Expected response (SSE frame) identifies the server and its capabilities:

event: message
data: {"jsonrpc":"2.0","id":1,"result":{"protocolVersion":"2025-06-18","serverInfo":{"name":"sigmap","version":"8.9.1",...},"capabilities":{"tools":{}}}}

The response also carries an mcp-session-id header; reuse it (plus a notifications/initialized POST) to call tools/list, which returns all 19 sigmap tools (read_context, search_signatures, get_lines, …).

Use from Cursor

Add to ~/.cursor/mcp.json (global) or .cursor/mcp.json (project), then enable it under Settings → Tools & MCP:

{
  "mcpServers": {
    "sigmap": {
      "url": "http://localhost:8765/mcp"
    }
  }
}

Verify from the CLI with cursor-agent mcp list (expect sigmap: ready).

How indexing works

sigmap runs inside the mounted /workspace and reads its generated context files from disk on every MCP call. The container builds an initial index on startup; to refresh it after changing files, either restart the container or re-run generation inside it:

podman exec -w /workspace sigmap-mcp sigmap

Generated artifacts (.github/copilot-instructions.md, .context/, PROJECT_MAP.md) are written into your mounted repo and, thanks to --userns=keep-id, are owned by your host user.