# Environment variables Every environment variable that changes how the Inspector behaves at runtime, in one place: the Inspector's own variables, plus the standard system and Node variables it reads (`HOME`, the proxy variables, the Node TLS variables). Set them in the shell that launches `mcp-inspector` (or with `-e` for the [Docker image](./docker.md)). The **Read by** column names the client whose process reads the variable: **web** is the Node backend that `--web` starts (the browser itself reads no environment), **CLI** and **TUI** are those clients, and **launcher** is the `mcp-inspector` bin that picks one of them. A variable read in shared `core/` code is marked with every client that reaches it. ⚠️ **Unset a variable rather than setting it to an empty string.** The two are not interchangeable: `HOST=""` is read as an all-interfaces bind and refused, and an empty path variable such as `MCP_STORAGE_DIR=` or `MCP_INSPECTOR_LOG_DIR=` can resolve relative to the working directory instead of falling back to the default. A row says so explicitly where an empty value is treated as unset. A `~` in a default below means the home directory as described under [Home directory](#home-directory). ## Authentication and network exposure These guard the web backend, which spawns processes on request. Read [Host binding and the origin allow-list](../clients/web/README.md#host-binding--the-origin-allow-list) before widening any of them. | Variable | Read by | Default | Effect | | --------------------------------- | -------- | ------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `MCP_INSPECTOR_API_TOKEN` | web, CLI | a random token per launch | Bearer token guarding every `/api/*` route (`x-mcp-remote-auth: Bearer `). Set it to use a known token instead of the generated one printed in the launch banner. The CLI reads it only to fill the `autoConnect` parameter of the deep link it emits. | | `MCP_PROXY_AUTH_TOKEN` | web | — | **Deprecated** v1 name for `MCP_INSPECTOR_API_TOKEN`, used only when the new name is unset. | | `DANGEROUSLY_OMIT_AUTH` | web | unset | Disables the API token entirely. ⚠️ **Any non-empty value turns auth off, including `false` and `0`** — unset the variable to keep auth on. | | `HOST` | web, CLI | `127.0.0.1` | Address the web server binds. An all-interfaces host (`0.0.0.0`, `::`, an empty string, and equivalent spellings) is **refused** unless `DANGEROUSLY_BIND_ALL_INTERFACES` is enabled. The CLI reads it only to build its deep link. | | `DANGEROUSLY_BIND_ALL_INTERFACES` | web | off | Opts in to an all-interfaces `HOST`. Only `true` or `1` (case-insensitive) enable it, so `false` reads as off. The Docker image sets it. | | `ALLOWED_ORIGINS` | web | derived from `HOST` | Comma-separated origins allowed to call the API. Unset, the list follows `HOST` at `CLIENT_PORT`: the loopback origins for a loopback host, the loopback origins plus `http://0.0.0.0` and `http://[::]` for an all-interfaces bind, and otherwise only the configured host's own origin (so binding a LAN address does **not** also allow `localhost`). **Replaces** the default list rather than adding to it, so list every form you browse from. Each entry must include the scheme (`http://localhost:6274`). | ## Ports | Variable | Read by | Default | Effect | | --------------------- | -------- | ------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `CLIENT_PORT` | web, CLI | `6274` | Web UI port. Must be a **fixed** integer in 1–65535: `0` (an OS-assigned port) is rejected at startup, because the origin allow-list and the MCP Apps sandbox CSP are derived from it. | | `MCP_SANDBOX_PORT` | web, CLI | `6275` | Port of the MCP Apps sandbox server, 0–65535. `0` asks the OS for a free port. An invalid value is ignored with a warning. | | `SERVER_PORT` | web | — | v1's proxy port, now only a fallback for the sandbox port: used whenever `MCP_SANDBOX_PORT` does not yield a valid port — unset, empty, **or invalid**. | | `MCP_APP_ORIGIN_PORT` | web, CLI | `6278` | Port of the dedicated app-origin server, used only by an MCP App whose UI resource declares `_meta.ui.domain`; 0–65535, where `0` asks the OS for a free port. An invalid value is ignored with a warning. Pin it if your app's backend allowlists that origin. | The sandbox port resolves as: a valid `MCP_SANDBOX_PORT`, else a valid `SERVER_PORT`, else `6275`. The CLI reads `CLIENT_PORT`, `MCP_SANDBOX_PORT`, `MCP_APP_ORIGIN_PORT` and `HOST` only to build the deep link and port list it hands to a web session; it binds none of them. It normalizes `HOST` (an all-interfaces host becomes `localhost`, any other host is canonicalized), but it validates none of the three **port** variables: any non-empty port value is copied into the URLs and port-forwarding command as-is, with no range check, no warning, and no `SERVER_PORT` fallback, so a malformed value produces a broken hand-off rather than an error. ## Behavior | Variable | Read by | Default | Effect | | ------------------------ | ------------- | -------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `MCP_AUTO_OPEN_ENABLED` | web, CLI | see effect | Whether a browser is opened for you. `false` never opens one; `true` always does. Unset (or any other value), the web client opens the UI at launch, and the CLI opens the OAuth authorization page only when stderr is a TTY. In the CLI, `true` also lets interactive OAuth **start** when neither stdin nor stderr is a TTY; otherwise that case fails with an auth-required error pointing at `--stored-auth-only`. **The TUI does not read it** and always opens the OAuth page. | | `MCP_CATALOG_PATH` | web, CLI, TUI | `~/.mcp-inspector/mcp.json` | Default writable catalog, used when no `--catalog` is given. The CLI honors it only when no ad-hoc target (positional command, `--server-url`, or `--transport`) is given. See [MCP server configuration](./mcp-server-configuration.md). | | `MCP_OAUTH_CALLBACK_URL` | CLI, TUI | `http://127.0.0.1:6276/oauth/callback` | Loopback redirect URL for the CLI/TUI OAuth flow. `--callback-url` takes precedence. | | `NO_COLOR` | CLI | unset | Any non-empty value disables ANSI styling in the CLI's human-readable output. An empty `NO_COLOR=` counts as unset. | ## Storage and state | Variable | Read by | Default | Effect | | -------------------------------- | ------------- | -------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `MCP_STORAGE_DIR` | web, CLI, TUI | `~/.mcp-inspector/storage` | Storage directory. Relocates the OAuth state file (`oauth.json`) and the secrets file (`secrets.json`) for every client. For the **web** backend it also relocates `client.json`; the CLI and TUI find `client.json` through `MCP_CLIENT_CONFIG_PATH` instead. | | `MCP_INSPECTOR_OAUTH_STATE_PATH` | CLI, TUI | `~/.mcp-inspector/storage/oauth.json` | Names the OAuth state file outright. Lookup order: this variable, then `/oauth.json`, then `~/.mcp-inspector/storage/oauth.json`. ⚠️ Setting `MCP_STORAGE_DIR` alone does not isolate a CLI or TUI run if this variable is also exported. **The web backend does not read it** — it always uses `/oauth.json`. | | `MCP_CLIENT_CONFIG_PATH` | CLI, TUI | `~/.mcp-inspector/storage/client.json` | Install-level client config (CIMD, enterprise IdP). `--client-config` takes precedence. | ### Home directory Every default above that starts with `~` is built from the home directory the process sees, not from the OS account database: | Variable | Read by | Effect | | ------------- | ------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | | `HOME` | web, CLI, TUI | Base of `~/.mcp-inspector`: the default catalog, storage directory (`oauth.json`, `client.json`), secrets file, and TUI log directory. | | `USERPROFILE` | web, CLI, TUI | Used in place of `HOME` when `HOME` is unset or empty — the normal case on Windows. ⚠️ If **neither** is set, as under some service managers, those defaults resolve against the **current working directory** instead. Set `HOME` or the specific path variables above. | ## Secret store Where server secrets (headers, client secrets) are kept. The details — the keychain probe, the file format, encryption and locking — are in the [Docker guide](./docker.md); these variables apply to every install, not only containers. | Variable | Read by | Default | Effect | | ---------------------------- | ------------- | --------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `MCP_INSPECTOR_SECRET_STORE` | web, CLI, TUI | probe the OS keychain | `keyring`, `file`, or `memory` (case-insensitive) picks the store outright and skips the probe. An empty or whitespace-only value counts as unset and silently runs automatic selection; any other value is ignored with a warning and also falls back to automatic selection. | | `MCP_INSPECTOR_SECRET_FILE` | web, CLI, TUI | `~/.mcp-inspector/secrets.json` | Path of the file store. Lookup order: this variable, then `secrets.json` in `MCP_STORAGE_DIR` when that is set, then `~/.mcp-inspector/secrets.json`. ⚠️ The default sits **beside** the storage directory, not inside it. | | `MCP_INSPECTOR_SECRET_KEY` | web, CLI, TUI | unset (file is plaintext, `0600`) | Passphrase that encrypts the file store; an empty or whitespace-only value counts as unset. Use a generated, high-entropy value. ⚠️ Changing or losing it makes the existing file unreadable; see the Docker guide before rotating it. | When no store is configured, the choice also depends on whether the Inspector is running in a container, which it detects from `KUBERNETES_SERVICE_HOST` (or Docker's and Podman's marker files). That variable is set by the orchestrator, not by you. ## Logging and debugging | Variable | Read by | Default | Effect | | ----------------------- | ------------- | ------------------ | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `MCP_DEBUG` / `DEBUG` | launcher, TUI | off | Prints the full stack trace when the process exits on an error — the launcher for any `--web`/`--tui` failure, and the standalone TUI entry point for a startup failure. Any value other than empty, `0` or `false` (case-insensitive) turns it on. | | `MCP_LOG_FILE` | web | unset (no log) | Appends the web backend's structured (pino, JSON lines) log to this file, creating its directory if needed. An empty value counts as unset. | | `MCP_INSPECTOR_LOG_DIR` | TUI | `~/.mcp-inspector` | Directory of the TUI's `auth.log`. The TUI logs to a file so its output does not corrupt the terminal UI. | | `LOG_LEVEL` | TUI | `info` | Level of the TUI's `auth.log`: one of `trace`, `debug`, `info`, `warn`, `error`, `fatal`, `silent`. An empty value is not replaced by `info`. | ## Outbound proxy | Variable | Read by | Default | Effect | | ---------------------------- | ------------- | ------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `HTTPS_PROXY` / `HTTP_PROXY` | web, CLI, TUI | unset | Route connections to remote HTTP/SSE servers, including OAuth discovery and token requests, through a proxy. Lowercase forms are honored too. See [HTTP proxy support](../clients/cli/README.md#http-proxy-support). | | `NO_PROXY` | web, CLI, TUI | unset | Hosts exempted from the proxy. | ## Node.js variables These belong to Node, not the Inspector, but they are the answer to some common connection problems. Because the web client connects to MCP servers **from its Node backend**, not from the browser, they apply to all three clients. ### Connecting to a server with a self-signed certificate A server at `https://localhost`, or anywhere else with a self-signed or privately issued certificate, fails to connect with a generic fetch error, because Node does not trust the certificate. Trusting the browser's exception does not help — the browser is not the one connecting ([#1936](https://github.com/modelcontextprotocol/inspector/issues/1936)). **Prefer trusting the certificate's CA.** `NODE_EXTRA_CA_CERTS` adds certificates to the ones Node trusts, and leaves verification on for every other connection: ```sh NODE_EXTRA_CA_CERTS=/path/to/your-ca.pem npx @modelcontextprotocol/inspector ``` For a self-signed certificate with no separate CA, point it at the certificate itself. Node reads the variable once at startup, so it must be set before launching. **Or turn verification off, for local development only:** ```sh NODE_TLS_REJECT_UNAUTHORIZED=0 npx @modelcontextprotocol/inspector ``` ⚠️ This disables certificate verification for **every** TLS connection the Inspector process makes — every MCP server, every OAuth authorization server and token endpoint — not just the one you are testing, and Node prints a warning saying so. A connection that would have been refused for impersonation is then accepted. Never set it in a shell profile, a shared environment, or a deployment. | Variable | Default | Effect | | ------------------------------ | ------- | ----------------------------------------------------------------------------------------------------- | | `NODE_EXTRA_CA_CERTS` | unset | PEM file of extra CA certificates to trust, in addition to Node's bundled ones. Read once at startup. | | `NODE_TLS_REJECT_UNAUTHORIZED` | `1` | `0` disables TLS certificate verification for the whole process. Development only. |