MCP Inspector CLI Client

CLI for the Inspector: connect, run a --method, disconnect. Invoked as mcp-inspector --cli.

Running the CLI

You can run the CLI via npx:

npx @modelcontextprotocol/inspector --cli node build/index.js

Supports tools, resources, and prompts (plus --method servers/list / servers/show for catalog entries without connecting).

Examples

Basic usage

npx @modelcontextprotocol/inspector --cli node build/index.js

With a configuration file

npx @modelcontextprotocol/inspector --cli --config path/to/config.json --server myserver

List available tools

npx @modelcontextprotocol/inspector --cli node build/index.js --method tools/list

Call a specific tool

npx @modelcontextprotocol/inspector --cli node build/index.js --method tools/call --tool-name mytool --tool-arg key=value --tool-arg another=value2

Call a tool with JSON arguments

npx @modelcontextprotocol/inspector --cli node build/index.js --method tools/call --tool-name mytool --tool-arg 'options={"format": "json", "max_tokens": 100}'

List available resources

npx @modelcontextprotocol/inspector --cli node build/index.js --method resources/list

List available prompts

npx @modelcontextprotocol/inspector --cli node build/index.js --method prompts/list

Remote Servers

You can also connect to remote MCP servers using HTTP or SSE transports.

Connect to a remote MCP server (default is SSE)

npx @modelcontextprotocol/inspector --cli https://my-mcp-server.example.com

Connect with Streamable HTTP transport

npx @modelcontextprotocol/inspector --cli https://my-mcp-server.example.com --transport http --method tools/list

Pass custom headers

npx @modelcontextprotocol/inspector --cli https://my-mcp-server.example.com --transport http --method tools/list --header "X-API-Key: your-api-key"

When a server is loaded from a --catalog/--config file, its per-server settings (headers, connection/request timeouts, OAuth, and roots) are applied to the connection — the same resolution the TUI uses. A --header flag overrides the file's headers for that run while leaving the file's timeouts and OAuth in place.

The file is the only durable way to give a run its roots: there is no roots flag, and --method roots/set applies only to that one short-lived connection. Roots configured for a server (the same field the web UI's Server Settings writes) are advertised at connect, so a server that asks for roots/list — @modelcontextprotocol/server-filesystem does, to learn its allowed directories — gets them.

Environment-variable semantics. MCP_CATALOG_PATH is honored only when no ad-hoc target is given (positional command, --server-url, or --transport) — so a shell that exports it can still run one-off ad-hoc invocations without hitting the catalog/ad-hoc conflict. MCP_STORAGE_DIR sets the storage directory used by the OAuth persist backend (<MCP_STORAGE_DIR>/oauth.json); the per-file MCP_INSPECTOR_OAUTH_STATE_PATH override still takes precedence over it.

HTTP proxy support

Connections to remote HTTP/SSE servers honor the conventional proxy environment variables: HTTPS_PROXY / HTTP_PROXY (and their lowercase forms) select the proxy, and NO_PROXY exempts hosts. This applies to the Node transport shared by the CLI and the web backend — no inspector-specific flag is needed. When a proxy variable is set, outbound requests are routed through undici's EnvHttpProxyAgent.

Proxy routing is powered by the undici package (^8.5.0, which requires Node >= 22.19.0 — the inspector's supported floor). It is imported lazily only when a proxy variable is set, so runs without a proxy configured pay no cost.

Options

MCP server (which server to connect to)

Options that specify the MCP server (catalog/config file, ad-hoc command/URL, env vars, headers) are shared by the Web, CLI, and TUI and are documented in MCP server configuration: --catalog (writable catalog, seeded empty if missing; default ~/.mcp-inspector/mcp.json or MCP_CATALOG_PATH), --config (read-only session, errors if absent), --server, -e, --cwd, --header, --transport, --server-url, and the positional [target...]. --catalog and --config are mutually exclusive, and neither combines with an ad-hoc target.

CLI-specific (what to invoke)

Option	Description
--method <method>	MCP method to invoke. Supports initialize (connect-only probe → {serverInfo, protocolVersion, capabilities, instructions}), tools/list, tools/call, resources/list, resources/read, resources/templates/list, prompts/list, prompts/get, logging/setLevel, plus catalog-only servers/list / servers/show (no MCP connect). Stream / session-only methods (e.g. logging/tail) are rejected.
--tool-name <name>	Tool name (for tools/call).
--tool-arg <key=value>	Tool argument; repeat for multiple. Use key='{"json":true}' for JSON. Values are coerced (JSON-parsed, so count=1 becomes a number).
--tool-args-json <json>	Tool arguments as a single JSON object (e.g. '{"zip":"10001"}'). Passed verbatim — no key=value coercion, so "012" stays a string. Mutually exclusive with --tool-arg.
--uri <uri>	Resource URI (for resources/read).
--prompt-name <name>	Prompt name (for prompts/get).
--prompt-args <key=value>	Prompt arguments; repeat for multiple.
--log-level <level>	Logging level for logging/setLevel (e.g. debug, info).
--metadata <key=value>	General metadata (key=value); applied to all methods.
--tool-metadata <key=value>	Tool-specific metadata for tools/call.
--connect-timeout <ms>	Connection timeout in ms. Defaults to 15000 for ad-hoc --server-url/target runs (so a black-holed host fails fast) and to the file-level timeout for --catalog/--config runs. 0 disables the timeout.
--app-info	Probe a tool's MCP App UI metadata without invoking it. With --method tools/call --tool-name <name>: prints one JSON line (hasApp, resourceUri, csp, permissions, domain, …) and exits 0 if the tool has an app or 2 (no_app) if not. With --method tools/list: emits NDJSON — one app-info line per tool over a single connection.
--format <text|json>	Output format. text (default) pretty-prints the result. json emits a single JSON object on stdout ({ "result": … }, plus { "appInfo": … } as a sibling key for App tools) with no banners, so the whole output pipes cleanly into jq.
--relogin	Delete stored OAuth for this server URL from the shared store before connect; interactive login still only runs if the server requires auth. Requires an HTTP/SSE URL (rejected for stdio). Conflicts with --stored-auth-only / --use-stored-auth / --wait-for-auth / catalog short-circuits.
--stored-auth-only	CI / non-interactive safe: never start interactive OAuth / step-up (and never auto-open a browser); use the shared store if present, otherwise fail immediately with auth_required. Prefer this over a bare pipe/CI run that would otherwise attempt interactive login.

servers/show redacts secret-bearing fields (env values, sensitive headers / settings.metadata keys, requestInit / eventSourceInit headers, oauthClientSecret). It does not scrub credentials embedded in a server url (userinfo or query tokens) or in stdio args — treat detail / raw URL fields as potentially sensitive before pasting into issues.

App probing (--app-info) and machine-readable output (--format json)

--app-info inspects a tool's MCP App UI posture without calling the tool, so a pipeline can decide whether to open a browser before touching one:

# Probe one tool. Exits 0 (has app) or 2 (no_app). One JSON line on stdout.
mcp-inspector --cli <server> --method tools/call --tool-name my_tool --app-info
# → {"hasApp":true,"toolName":"my_tool","resourceUri":"ui://…","csp":{…},"permissions":{…},"prefersBorder":true,"resourceMimeType":"text/html"}

# Probe every tool at once — NDJSON, one line per tool, single connection.
mcp-inspector --cli <server> --method tools/list --app-info | jq -c 'select(.hasApp)'

Exit semantics: a tool that has an app exits 0; one with no app exits 2 (no_app); a missing tool exits 5 (tool_not_found) — distinct so a typo isn't mistaken for "no app". A probe failure (an unreadable UI resource, or a malformed _meta.ui.resourceUri) is tolerated and reported in a resourceError field rather than aborting — so in tools/list --app-info one bad tool never kills the rest of the listing.

--format json wraps any method's output in a single stdout envelope with no banners, so App tools and plain tools both pipe cleanly into jq:

mcp-inspector --cli <server> --method tools/call --tool-name my_app_tool --format json
# → {"result":{…tool result…},"appInfo":{"hasApp":true,"resourceUri":"ui://…",…}}

tools/list --app-info always emits NDJSON (one raw app-info object per line) regardless of --format — the per-tool list shape is fixed. --format json only reshapes the single-result paths (tools/call, tools/list without --app-info, etc.) into the {result[, appInfo]} envelope.

A tools/call that returns isError:true still prints its payload but exits 5 (tool_is_error) so && chains don't proceed on a failed call.

CLI-specific (OAuth for HTTP servers)

The CLI runs the same loopback callback server as the TUI (http://127.0.0.1:6276/oauth/callback by default).

CLI (mcp-inspector --cli): on connect 401 or mid-session interactive auth (re-login / step-up), it:

1. Starts the callback listener on --callback-url (or MCP_OAUTH_CALLBACK_URL)
2. Prints the authorization URL to stderr (OSC 8 hyperlink when stderr is a TTY) and opens the default browser when allowed. Default: open on a stderr TTY (so 2>&1 | tee prints a plain URL into the log but does not auto-open); plain URL only when stderr is non-TTY. MCP_AUTO_OPEN_ENABLED=false never opens; =true forces open even on a non-TTY (same as the web launcher).
3. Waits for the browser redirect, exchanges the code, and retries connect or the failed RPC

Interactive OAuth (connect-time or mid-RPC) requires a TTY on stdin or stderr (so 2>&1 | tee still works — stdin stays a TTY), or MCP_AUTO_OPEN_ENABLED=true. When neither stdin nor stderr is a TTY and that env is unset (typical CI), the CLI fails fast with auth_required instead of waiting up to 15 minutes on the loopback callback. Use --stored-auth-only for non-interactive runs that should only consume the shared store.

Step-up (standard OAuth): when an RPC needs extra scopes, the CLI prompts on stderr: Proceed with step-up authorization? [y/N]. y continues (including piped stdin — echo y | … or printf y | …); N or EOF with no answer (< /dev/null / Ctrl-D) declines. Piped answers must be newline-terminated, or stdin must close — a bare y held open without \n or EOF is not flushed as a line and times out. A non-TTY stdin that never sends a line within 5 seconds fails with auth_required (timed out, not the same as an explicit N). Answering y only confirms step-up — the following browser/loopback OAuth can still wait up to 15 minutes; for headless CI prefer --stored-auth-only with tokens already in the store. EMA step-up re-mints silently (no prompt).

Shared OAuth storage: the CLI reuses tokens from ~/.mcp-inspector/storage/oauth.json when they already exist (same file as other Inspector clients). That is passive file sharing, not launching another app.

Shared with TUI (config only, not interactive login):

• Per-server OAuth fields from mcp.json (static client, EMA resource credentials, scopes)
• Install-level settings from ~/.mcp-inspector/storage/client.json (or --client-config / MCP_CLIENT_CONFIG_PATH) — EMA IdP, CIMD
• CLI flags --client-id, --client-secret, --client-metadata-url override client.json when set
• Keychain-backed secrets in mcp.json are rehydrated on catalog load (same as TUI)

OAuth callback URL

Surface	Default callback
Web	http://localhost:6274/oauth/callback
TUI	http://127.0.0.1:6276/oauth/callback (interactive — callback server)
CLI	http://127.0.0.1:6276/oauth/callback (interactive — same callback server as TUI)

Register http://127.0.0.1:6276/oauth/callback on static or enterprise IdPs that require pre-registered redirect URIs before using the TUI or CLI. Override with --callback-url or MCP_OAUTH_CALLBACK_URL. Only one process should bind the default port at a time.

Flags

Option	Env	Description
--client-config <path>	MCP_CLIENT_CONFIG_PATH	Install-level client config (default: ~/.mcp-inspector/storage/client.json).
--client-id <id>	—	OAuth client ID (static client); overrides client.json.
--client-secret <secret>	—	OAuth client secret; overrides client.json.
--client-metadata-url <url>	—	CIMD metadata URL; overrides client.json.
--callback-url <url>	MCP_OAUTH_CALLBACK_URL	Redirect URI sent to the authorization server (default: http://127.0.0.1:6276/oauth/callback). Must bind a loopback host (localhost / 127.0.0.0/8 / [::1]) — the listener receives the authorization code over plaintext http, so a non-loopback host hard-errors (no opt-in; use a port-forward if the browser is elsewhere).
—	MCP_AUTO_OPEN_ENABLED	Browser auto-open and non-TTY interactive-OAuth admit: true (allow interactive OAuth without a TTY and force-open the browser — same as the web launcher), false (never open), unset (open on a TTY unless VITEST is set). For CI that must not hang, prefer --stored-auth-only.

Example — list tools on an OAuth-protected server using stored tokens and CIMD from the command line:

npx @modelcontextprotocol/inspector --cli --catalog mcp.json --server my-http-server \
  --client-metadata-url https://example.com/.well-known/oauth/client-metadata.json \
  --method tools/list

See EMA / enterprise-managed auth and OAuth smoke testing (§3 Stytch/CIMD; §5 mid-session manual validation — CLI C1–C2).

Stored-auth (web → CLI handoff)

For the common case where OAuth was already completed in the web inspector on the same machine, the CLI can reuse the resulting token instead of running its own interactive flow. It reads the shared OAuth state file (the oauth.json the web backend writes) directly from disk and injects Authorization: Bearer <token> for --server-url.

Option	Description
--use-stored-auth	Read the stored auth for --server-url and inject Authorization: Bearer. When a refresh_token is stored, the CLI runs the OAuth refresh grant first and injects the fresh access token (persisting the rotation); otherwise it injects the stored access token. Exits 3 (no_stored_token) — listing the stored keys — when nothing matches. Requires --server-url.
--wait-for-auth <sec>	Poll the OAuth state file (500 ms interval) until an access token for --server-url appears, then inject it. Times out at <sec> with exit 3 (auth_wait_timeout). Use after handing off to a human to complete OAuth in a browser. Unlike --use-stored-auth, this injects the freshly-landed access token directly (a token that just completed the browser flow is not expired), so it does not run the refresh grant.
--list-stored-auth	Print { oauthStatePath, storedServerUrls } (the server keys that currently have a token) and exit. No server connection is made.
--print-handoff	Print a JSON handoff block (deepLink, portForwardCmd, oauthStatePath, apiToken) for --server-url and exit — everything a script/remote VM needs to drive the browser-side OAuth dance. Requires --server-url.

State-file resolution follows MCP_INSPECTOR_OAUTH_STATE_PATH → <MCP_STORAGE_DIR>/oauth.json → ~/.mcp-inspector/storage/oauth.json — the same precedence the rest of the Inspector uses, so the CLI and web backend agree on the file. Server keys are canonicalised with new URL().href (the scheme the web store writes), so a trailing-slash or case mismatch between the URL a human opened and the one the agent passed still resolves.

Token refresh (#1665). When the stored server state carries a refresh_token (plus the clientInformation the web inspector persists after a completed flow), --use-stored-auth runs the SDK's OAuth refresh_token grant to mint a fresh access token before connecting, then writes the rotated tokens back to the state file (owner-only 0o600, via the shared store writer) so web and CLI stay consistent. The auth-server metadata is reused from the stored state, or discovered from --server-url when absent. This covers both an absent and an expired stored access token — the persisted blob carries no expiry, so the refresh token is treated as the durable credential. If the refresh fails (revoked token, transient auth-server error) and a stored access token is also present, the CLI falls back to injecting that token rather than hard-failing; only when there is nothing to fall back on does it exit 3 (auth_required, envelope refresh_failed). Without a stored refresh_token the access token is injected as-is, and a stale one surfaces as an HTTP 401 → exit 3.

Because there is no stored expiry, a refresh_token is refreshed on every --use-stored-auth run. Two consequences with rotating refresh tokens: two concurrent invocations against the same state file race the single-use token (one wins), and a crash between a successful grant and the write-back leaves the rotated token unsaved. Both are narrow; re-authorize in the web inspector to recover.

Short-circuit modes. --list-stored-auth and --print-handoff each print their output and exit without connecting to a server; they ignore the method/target flags. They are mutually exclusive — if both are passed, --list-stored-auth takes precedence.

The deepLink is the canonical web deep-link (#1576) — http://<host>:<port>/?serverUrl=<url>&transport=<http|sse>&autoConnect=<token> — so navigating it in a browser reaches a connected inspector in one shot. transport is derived from the resolved server (--transport, else auto-detected from the URL path: /sse → sse, else http), not hardcoded. autoConnect is set to MCP_INSPECTOR_API_TOKEN; when that env var is unset the link is still emitted but a note field flags that the web app's autoConnect gate will reject it until the inspector is launched with a known token.

# On a remote VM: print what a human needs to complete OAuth in their browser.
mcp-inspector --cli --server-url https://api.example/mcp --print-handoff

# Then block until the token lands and run the call with it.
mcp-inspector --cli --transport http --server-url https://api.example/mcp \
  --wait-for-auth 120 --method tools/list

Exit codes & error envelopes

Every non-zero exit maps to a stable failure class, so a programmatic caller (CI, a script, an agent) can branch on why the CLI failed without scraping prose from stderr:

Code	Meaning
0	Success.
1	Usage / unexpected error (the catch-all).
2	No MCP App found on the tool (--app-info probe).
3	Server requires authentication (401/403, WWW-Authenticate, OAuth).
4	Server unreachable (DNS, connection refused, timeout, fetch failed).
5	Tool error (tools/call returned isError:true, or the tool was not found).

On any non-zero exit the CLI also writes a single JSON line to stderr — the ErrorEnvelope:

{
  "error": {
    "code": "auth_required",
    "message": "Unauthorized",
    "status": 401,
    "url": "https://api.example/mcp"
  }
}

The code is a stable identifier for the failure class; message is the human-readable error; cause, status, and url are included when known. Because it is one line, a caller can parse it with 2>&1 | tail -1 | jq .error.

Why use the CLI?

While the Web Client provides a rich visual interface, the CLI is designed for:

• Automation: Ideal for CI/CD pipelines and batch processing.
• AI Coding Assistants: Provides a direct, machine-readable interface (JSON) for tools like Cursor or Claude to verify changes immediately.
• Log Analysis: Easier integration with command-line utilities (like jq) to process and analyze MCP server output.

Development

Like the other clients, the CLI self-validates from its own folder:

npm run validate       # format:check && lint && typecheck && test  (fast; no coverage gate)
npm test               # build test-servers + binary, then run all tests
npm run test:coverage  # build + tests under the per-file ≥90 coverage gate

The CLI's test / test:coverage build the binary first (out-of-process e2e.test.ts spawns it). validate is format:check && lint && typecheck && test with no separate build step (pretest builds). Repo-root validate:cli delegates here; the coverage gate is npm run coverage / coverage:cli (also in npm run ci), matching AGENTS.md.

Tests run the CLI in-process (importing runCli()) so src/ is measured under coverage, with a thin out-of-process spawn layer for the real binary. See __tests__/README.md for details.