chatgpt-mcp-bridge

A small self-hosted MCP server that gives ChatGPT (Developer Mode / custom connectors) read-only access to a few free public data sources:

WHOIS domain lookups (whois_domain)
UK Companies House company search and profile lookup (companies_house_search, companies_house_company)
SEC EDGAR US public filings, proxied through this same server from sec-edgar-mcp

Wikidata is not hosted here — it's already public at https://wd-mcp.wmcloud.org/mcp/, so just add that URL directly as a fourth ChatGPT connector.

Architecture

ChatGPT ──HTTPS (ngrok tunnel)──> bridge (Express, port 3939)
                                    ├── /mcp           whois + Companies House tools
                                    └── /sec-edgar/mcp ──proxy──> sec-edgar container (port 9870)

One public hostname serves both tool sets — a free ngrok account only grants one static domain, so SEC EDGAR is reverse-proxied under a sub-path instead of getting its own tunnel.

Built on the current official MCP TypeScript SDK pattern: @modelcontextprotocol/server + @modelcontextprotocol/express + @modelcontextprotocol/node.

Setup

1. Environment

cp .env.example .env

Fill in:

COMPANIES_HOUSE_API_KEY — free key from developer.company-information.service.gov.uk
SEC_EDGAR_USER_AGENT — your real name + email, e.g. Jane Doe ([email protected]) (SEC requires a genuine identifying user-agent)
NGROK_AUTHTOKEN — from your ngrok dashboard
PUBLIC_HOSTNAME — your ngrok static domain (free accounts get exactly one, claimed once via the dashboard)

2. Run everything

docker compose up -d

Starts three containers: the bridge, the SEC EDGAR MCP server, and an ngrok tunnel pointing at the bridge.

3. Verify

docker compose logs -f
curl -s -X POST https://<your-domain>.ngrok-free.dev/mcp \
  -H 'Content-Type: application/json' -H 'Accept: application/json, text/event-stream' \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/list"}'

4. Register in ChatGPT

Settings → Apps → Advanced settings → enable Developer mode → add connectors (Streamable HTTP, no auth):

https://<your-domain>.ngrok-free.dev/mcp
https://<your-domain>.ngrok-free.dev/sec-edgar/mcp
https://wd-mcp.wmcloud.org/mcp/

Security notes

No-auth public endpoint: anyone holding the tunnel URL can call these tools while it's up. All tools here are read-only, but keep the URL private — don't post it anywhere public.
createMcpExpressApp's built-in DNS-rebinding protection is configured via PUBLIC_HOSTNAME in allowedHosts/allowedOrigins — requests with an unrecognized Host header get 403.
Keep COMPANIES_HOUSE_API_KEY and NGROK_AUTHTOKEN in .env only; never commit it (already gitignored).

Local dev (without Docker)

npm install
npm start          # bridge on :3939

SEC EDGAR needs to be running separately on :9870 for the /sec-edgar/mcp proxy to work — see docker-compose.yml for the exact command, or run the container manually:

docker run -i --rm -p 9870:9870 \
  -e SEC_EDGAR_USER_AGENT="Your Name ([email protected])" \
  stefanoamorelli/sec-edgar-mcp:latest \
  python -m sec_edgar_mcp.server --transport streamable-http --port 9870

chatgpt-mcp-bridge