inspector/clients/cli/README.md

MCP Inspector CLI Client

The CLI mode enables programmatic interaction with MCP servers from the command line. It is ideal for scripting, automation, continuous integration, and establishing an efficient feedback loop with AI coding assistants.

Running the CLI

You can run the CLI client directly via npx:

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

The CLI mode supports operations across tools, resources, and prompts, returning structured JSON output.

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, and OAuth) 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.

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 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 (e.g. tools/list, tools/call, resources/list, prompts/list).
--tool-name <name>	Tool name (for tools/call).
--tool-arg <key=value>	Tool argument; repeat for multiple. Use key='{"json":true}' for JSON.
--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.

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). 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 the console (ConsoleNavigation)
3. Waits for the browser redirect, exchanges the code, and retries connect or the failed RPC

Step-up (standard OAuth): when an RPC needs extra scopes, the CLI prompts on stderr: Proceed with step-up authorization? [y/N]. y continues; N exits with an error. 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).

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).

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 && test:coverage
npm test               # build test-servers + binary, then run all tests
npm run test:coverage  # build + tests under the per-file coverage gate

The CLI's test:coverage builds the binary first (its out-of-process e2e.test.ts spawns it, so it must run against a fresh build). validate therefore folds the build into test:coverage rather than repeating it — it is format:check && lint && test:coverage, with no separate build step (the other clients, whose tests don't spawn their bundle, keep an explicit build). The repo-root validate:cli just delegates here.

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.