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Merge pull request #1974 from modelcontextprotocol/v2/docs/1964-docker-loopback

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fix(docker): publish on loopback by default; make a mounted state dir writable
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Cliff Hall 2026-08-11 10:54:14 -04:00 • committed by GitHub
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clients/web/README.md
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@ -172,7 +172,7 @@ The guard blocks only the **wildcard** all-interfaces addresses. Binding a **spe
- **Bind a specific address.** `HOST=192.168.1.50` (a LAN IP) or a public IP works directly: the default origin allow-list follows the bind host, so `allowedOrigins` becomes `http://<that-host>:PORT` and a browser hitting that address is accepted with no extra config. (The host is canonicalized the way a browser is — so `HOST=127.1` advertises `http://127.0.0.1:PORT`, an IPv6 bind host is bracketed as `http://[2001:db8::1]:PORT`, and the port is dropped when it's the http default `:80` — matching what the browser sends.)
- **Behind TLS or a reverse proxy**, the browser's `Origin` becomes the public origin (e.g. `https://inspector.example.com`, often without a port), which won't match the auto-derived `http://<bind-host>:PORT`. Set `ALLOWED_ORIGINS` to the real public origin(s): `ALLOWED_ORIGINS=https://inspector.example.com`.
- **Using the `0.0.0.0` wildcard** (opt-in via `DANGEROUSLY_BIND_ALL_INTERFACES=true`, as the Docker image does): a wildcard bind also serves loopback, so the default allow-list is the loopback trio plus the canonical wildcard origins (`http://0.0.0.0:PORT`, `http://[::]:PORT`), and **local access works out of the box** — `docker run -p 6274:6274` browsed at `http://localhost:6274` connects with no extra config. Reaching it at a **non-loopback** address (a LAN IP, a public hostname) still needs `ALLOWED_ORIGINS` — but since that **replaces** the default, keep the loopback forms in the list if you also browse locally: `ALLOWED_ORIGINS=http://localhost:PORT,http://127.0.0.1:PORT,http://192.168.1.50:PORT,https://inspector.example.com`.
- **Using the `0.0.0.0` wildcard** (opt-in via `DANGEROUSLY_BIND_ALL_INTERFACES=true`, as the Docker image does): a wildcard bind also serves loopback, so the default allow-list is the loopback trio plus the canonical wildcard origins (`http://0.0.0.0:PORT`, `http://[::]:PORT`), and **local access works out of the box** — `docker run -p 127.0.0.1:6274:6274` browsed at `http://localhost:6274` connects with no extra config. Reaching it at a **non-loopback** address (a LAN IP, a public hostname) still needs `ALLOWED_ORIGINS` — but since that **replaces** the default, keep the loopback forms in the list if you also browse locally: `ALLOWED_ORIGINS=http://localhost:PORT,http://127.0.0.1:PORT,http://192.168.1.50:PORT,https://inspector.example.com`.
The bind-host guard and the `ALLOWED_ORIGINS` allow-list apply to both the prod server and `--dev`. Note that in **`--dev`** the Vite dev server _additionally_ enforces its own `server.allowedHosts` Host-header check, whose default accepts loopback and IP-literal hosts. The host you **bind** is auto-allowed (Vite adds the resolved `server.host` — which this config sets from `HOST` — to the allow-list), so `HOST=<hostname>` works out of the box under `--dev` too. What needs an explicit `server.allowedHosts` entry is reaching the dev server at a **different** name than the one bound — e.g. a wildcard bind reached by hostname, or a reverse-proxy domain. For those, prefer the prod server (`mcp-inspector --web`) or add the host to `server.allowedHosts`.