mcpc — a universal MCP CLI client

mcpc is a command-line client for the Model Context Protocol (MCP) that maps MCP operations to intuitive commands for interactive shell use, scripting, and AI agents.

mcpc is your new Swiss Army knife for MCP. It's great for manual inspection and debugging of MCP servers, as well as for agents to leverage all modern MCP capabilities through the most universal coding interface: the UNIX shell.

Key features:

• 🔧 Full MCP support - HTTP/stdio transports, instructions, tools, async tasks, resources, prompts, ...
• 🔄 Persistent sessions - Keep multiple stateful connections alive simultaneously.
• 🗺️ Progressive tool discovery - Find relevant MCP tools on the fly to save tokens and increase accuracy.
• 🔌 Code mode - JSON output composes with jq, xargs, and shell pipelines for MCP workflows as shell scripts.
• 🔒 Secure - Full OAuth 2.1 support with CMID and DCR, uses OS keychain for credentials storage.
• 🤖 AI sandboxing - Proxy MCP server connections to protect credentials from AI-generated code.
• 🪶 Lightweight - Minimal dependencies, works on Mac/Win/Linux, doesn't use LLMs on its own.
• 💸 Agentic payments - Experimental support for the x402 protocol on Base.

Table of contents

• Install
• Quickstart
• Usage
• Sessions
• Authentication
• MCP proxy
• AI agents
• Agentic payments (x402)
• MCP support
• Configuration
• Security
• Errors
• Development
• Related work
• License

Install

npm install -g @apify/mcpc

# Or with Bun
bun install -g @apify/mcpc

Linux users: mcpc uses the OS keychain for secure credential storage via the Secret Service API. On desktop systems (GNOME, KDE) this works out of the box. On headless/server/CI environments without a keyring daemon, mcpc automatically falls back to a file-based credential store (~/.mcpc/credentials, mode 0600).

To use the OS keychain on a headless system, install libsecret and a secret service daemon:

# Debian/Ubuntu
sudo apt-get install libsecret-1-0 gnome-keyring

# Fedora/RHEL/CentOS
sudo dnf install libsecret gnome-keyring

# Arch Linux
sudo pacman -S libsecret gnome-keyring

And then run mcpc as follows:

dbus-run-session -- bash -c "echo -n 'password' | gnome-keyring-daemon --unlock && mcpc ..."

Quickstart

# List all active sessions and saved authentication profiles
mcpc

# Login to remote MCP server and save OAuth credentials for future use
mcpc login mcp.apify.com

# Create a persistent session and interact with it
mcpc connect mcp.apify.com @test
mcpc @test                                            # show server info
mcpc @test tools-list
mcpc @test tools-call search-actors keywords:="website crawler"
mcpc @test shell

# Use JSON mode for scripting
mcpc --json @test tools-list

# Use a local MCP server package (stdio) referenced from config file
mcpc connect ./.vscode/mcp.json:filesystem @fs
mcpc @fs tools-list

Usage

Usage: mcpc [<@session>] [<command>] [options]

Universal command-line client for the Model Context Protocol (MCP).

Commands:
  connect <server> [@session]  Connect to an MCP server and start a named @session
  close <@session>             Close a session
  restart <@session>           Restart a session (losing all state)
  shell <@session>             Open interactive shell for a session
  login <server>               Interactively login to a server using OAuth and save profile
  logout <server>              Delete an OAuth profile for a server
  clean [resources...]         Clean up mcpc data (sessions, profiles, logs, all)
  grep <pattern>               Search tools and instructions across all active sessions
  x402 [subcommand] [args...]  Configure an x402 payment wallet (EXPERIMENTAL)
  help [command] [subcommand]  Show help for a specific command

Options:
  --json                       Output in JSON format for scripting
  --verbose                    Enable debug logging
  --profile <name>             OAuth profile for the server ("default" if not provided)
  --timeout <seconds>          Request timeout in seconds (default: 300)
  --max-chars <n>              Truncate output to n characters (ignored in --json mode)
  --insecure                   Skip TLS certificate verification (for self-signed certs)
  -v, --version                Output the version number
  -h, --help                   Display help

MCP session commands (after connecting):
  <@session>                   Show MCP server info, capabilities, and tools overview
  <@session> grep <pattern>    Search tools and instructions
  <@session> tools-list        List all server tools
  <@session> tools-get <name>  Get tool details and schema
  <@session> tools-call <name> [arg:=val ... | <json> | <stdin]
  <@session> prompts-list
  <@session> prompts-get <name> [arg:=val ... | <json> | <stdin]
  <@session> resources-list
  <@session> resources-read <uri>
  <@session> resources-subscribe <uri>
  <@session> resources-unsubscribe <uri>
  <@session> resources-templates-list
  <@session> tasks-list
  <@session> tasks-get <taskId>
  <@session> tasks-result <taskId>
  <@session> tasks-cancel <taskId>
  <@session> logging-set-level <level>
  <@session> ping

Run "mcpc" without arguments to show active sessions and OAuth profiles.
Run "mcpc --json" to get the same data as `{ sessions: [...], profiles: [...] }`.

General actions

With no arguments, mcpc lists all active sessions and saved OAuth profiles:

# List all sessions and OAuth profiles (also in JSON mode)
mcpc
mcpc --json

# Show command help or version
mcpc --help
mcpc --version

# Clean stale sessions and old log files
mcpc clean

Server formats

The connect, login, and logout commands accept a <server> argument in these formats:

• Remote URL (e.g. mcp.apify.com or https://mcp.apify.com) — scheme defaults to https://
• Config file entry (e.g. ~/.vscode/mcp.json:filesystem) — file:entry-name syntax

MCP commands

All MCP commands go through a named session created with connect:

# Connect to a remote server and create a session
mcpc connect mcp.apify.com @apify
mcpc @apify tools-list
mcpc @apify tools-call search-apify-docs query:="What are Actors?"

# Connect to a local server via config file entry
mcpc connect ~/.vscode/mcp.json:filesystem @fs
mcpc @fs tools-list
mcpc @fs tools-call list_directory path:=/

See MCP feature support for details about all supported MCP features and commands.

Command arguments

The tools-call and prompts-get commands accept arguments as positional parameters after the tool/prompt name:

# Key:=value pairs (auto-parsed: tries JSON, falls back to string)
mcpc @session tools-call <tool-name> greeting:="hello world" count:=10 enabled:=true
mcpc @session tools-call <tool-name> config:='{"key":"value"}' items:='[1,2,3]'

# Force string type with JSON quotes
mcpc @session tools-call <tool-name> id:='"123"' flag:='"true"'

# Inline JSON object (if first arg starts with { or [)
mcpc @session tools-call <tool-name> '{"greeting":"hello world","count":10}'

# Read from stdin (automatic when no positional args and input is piped)
echo '{"greeting":"hello","count":10}' | mcpc @session tools-call <tool-name>
cat args.json | mcpc @session tools-call <tool-name>

Rules:

• All arguments use := syntax: key:=value
• Values are auto-parsed: valid JSON becomes that type, otherwise treated as string
  • count:=10 → number 10
  • enabled:=true → boolean true
  • greeting:=hello → string "hello" (not valid JSON, so string)
  • id:='"123"' → string "123" (JSON string literal)
• Inline JSON: If first argument starts with { or [, it's parsed as a JSON object/array
• Stdin: When no positional args are provided and input is piped, reads JSON from stdin

Using shell variables:

When using shell variables that may contain spaces, use double quotes around the entire argument:

# Variable with spaces - use double quotes
QUERY="hello world"
mcpc @server tools-call search "query:=${QUERY}"

# Multiple variables
CITY="New York"
TYPE="restaurants"
mcpc @server tools-call search "query:=${CITY} ${TYPE}"

# For complex inputs, consider using JSON via stdin
echo "{\"query\": \"${QUERY}\", \"limit\": 10}" | mcpc @server tools-call search

Common pitfall: Don't put spaces around := - it won't work:

# Wrong - spaces around :=
mcpc @server tools-call search query := "hello world"

# Correct - no spaces around :=
mcpc @server tools-call search "query:=hello world"

Interactive shell

mcpc provides an interactive shell for discovery and testing of MCP servers.

mcpc @apify shell

Shell commands: help, exit/quit/Ctrl+D, Ctrl+C to cancel. Arrow keys navigate history (saved to ~/.mcpc/history).

Grep (search across sessions)

mcpc grep searches tools, resources, and prompts across all active sessions or within a single session:

# Search tools and server instructions in all active sessions
mcpc grep "search"

# Search within a single session
mcpc @apify grep "actor"

# Search resources and prompts instead of the default tools and instructions
mcpc grep "config" --resources --prompts

# Regex search
mcpc grep "search|find" -E

# Case-sensitive search (default is case-insensitive)
mcpc grep "Search" --case-sensitive

# Limit results
mcpc grep "e" -m 5

# JSON output for scripting
mcpc grep "actor" --json

By default, grep searches only tools. Use --resources or --prompts to search those types (combine with --tools to include tools too). Sessions that are crashed or unavailable are shown with their status rather than silently skipped.

The grep command is useful for dynamic tool discovery, also called Tool search tool by Anthropic or Dynamic context discovery by Cursor. Rather than loading all tools into AI agent's context, the agent can use grep to discover the right tool for the job, and only load the relevant tools into the context when needed to reduce token usage and improve accuracy.

JSON mode

By default, mcpc prints output in Markdown-ish text format with colors, making it easy to read by both humans and AIs.

With --json option, mcpc always emits only a single JSON object (or array), to enable scripting. For all MCP commands, the returned objects are always consistent with the MCP specification. On success, the JSON object is printed to stdout, on error to stderr.

Note that --json is not available for shell, login, and mcpc --help commands.

Sessions

MCP is a stateful protocol: clients and servers negotiate protocol version and capabilities, and then communicate within a persistent session. To support these sessions, mcpc can start a lightweight bridge process that maintains the connection and state. This is more efficient than forcing every MCP command to reconnect and reinitialize, and enables long-term stateful sessions.

The sessions are given names prefixed with @ (e.g. @apify), which then serve as unique reference in commands.

# Create a persistent session
mcpc connect mcp.apify.com @apify

# List all sessions and OAuth profiles
mcpc

# Run MCP commands in the session
mcpc @apify tools-list
mcpc @apify shell

# Restart the session (kills and restarts the bridge process)
mcpc @apify restart    # or: mcpc restart @apify

# Close the session, terminates bridge process
mcpc @apify close      # or: mcpc close @apify

# ...now session name "@apify" is forgotten and available for future use

Session lifecycle

The sessions are persistent: metadata is saved in ~/.mcpc/sessions.json file, authentication tokens in OS keychain. The mcpc bridge process keeps the session alive by sending periodic ping messages to the MCP server. Still, sessions can fail due to network disconnects, bridge process crash, or server dropping it.

Session states:

State	Meaning
🟢**live**	Bridge process running and server responding
🟡**connecting**	Initial bridge startup in progress (mcpc connect)
🟡**reconnecting**	Bridge crashed or lost auth; auto-reconnecting in the background
🟡**disconnected**	Bridge process running but server unreachable; auto-recovers when server responds
🟡**crashed**	Bridge process crashed or was killed; auto-reconnects in the background
🔴**unauthorized**	Server rejected authentication (401/403) or token refresh failed; auto-reconnects or needs login
🔴**expired**	Server rejected session ID (404); requires restart

Here's how mcpc handles various bridge process and server connection states:

• While the bridge process is running:
  • If server positively responds to pings, the session is marked 🟢 live, and everything is fine.
  • If server stops responding, the session is marked 🟡 disconnected. The bridge will keep trying to reconnect in the background and will return to 🟢 live once the server responds again.
  • If server rejects authentication (HTTP 401 or 403) or token refresh fails, the session is marked 🔴 unauthorized. mcpc will auto-reconnect in the background if another session sharing the same OAuth profile has refreshed the tokens. Otherwise, re-authenticate with mcpc login <server> and then mcpc @my-session restart.
  • If server rejects the session ID (HTTP 404), indicating the MCP session is no longer valid, the session is marked 🔴 expired. You need to restart the session with mcpc @my-session restart to establish a new connection.
• If the bridge process crashes, mcpc will mark the session as 🟡 crashed and auto-reconnect the bridge in the background. You can also trigger reconnection manually by running any mcpc @my-session ... command.
  • If reconnection succeeds and the server resumes the MCP session, the session returns to 🟢 live.
  • If the server issues a new session ID instead of resuming, the session is marked 🔴 expired.
  • If reconnection fails, the session remains 🟡 crashed and retries after a 10-second cooldown.

Note that mcpc never automatically removes sessions from the list. Instead, it keeps them flagged as 🟡 crashed, 🔴 unauthorized, or 🔴 expired, and any future attempts to use them will show the appropriate error with recovery instructions.

To remove the session from the list, you need to explicitly close it:

mcpc @apify close    # or: mcpc close @apify

You can restart a session anytime, which kills the bridge process and opens new connection with new MCP-Session-Id, by running:

mcpc @apify restart  # or: mcpc restart @apify

Authentication

mcpc supports all standard MCP authorization methods.

Anonymous access

For local servers (stdio) or remote servers (Streamable HTTP) which do not require credentials, mcpc can be used without authentication:

mcpc connect mcp.apify.com @test
mcpc @test tools-list

Bearer token authentication

For remote servers that require a Bearer token (but not OAuth), use the --header flag to pass the token. All headers are stored securely in the OS keychain for the session, but they are not saved as reusable OAuth profiles. This means --header needs to be provided whenever running a one-shot command or connecting new session.

# Create session with Bearer token (token saved to keychain for this session only)
mcpc connect https://mcp.apify.com @apify --header "Authorization: Bearer ${APIFY_TOKEN}"

# Use the session (Bearer token is loaded from keychain automatically)
mcpc @apify tools-list

OAuth profiles

For OAuth-enabled remote MCP servers, mcpc implements the full OAuth 2.1 flow with PKCE as mandated by the MCP authorization spec: WWW-Authenticate 401 challenges, Protected Resource Metadata and authorization server metadata discovery, all three client registration approaches, resource indicators (RFC 8707), and automatic refresh-token rotation.

The OAuth authentication always needs to be initiated by the user calling the login command, which opens a web browser with login screen. mcpc never opens the web browser on its own.

The OAuth credentials to specific servers are securely stored as authentication profiles - reusable credentials that allow you to:

• Authenticate once, use credentials across multiple commands or sessions
• Use different accounts (profiles) with the same server
• Manage credentials independently from sessions

Key concepts:

• Authentication profile: Named set of OAuth credentials for a specific server (stored in ~/.mcpc/profiles.json + OS keychain)
• Session: Active connection to a server that may reference an authentication profile (stored in ~/.mcpc/sessions.json)
• Default profile: When --profile is not specified, mcpc uses the authentication profile named default

Example:

# Login to server and save 'default' authentication profile for future use
mcpc login mcp.apify.com

# Use named authentication profile instead of 'default'
mcpc login mcp.apify.com --profile work

# Create two sessions using the two different credentials
mcpc connect mcp.apify.com @apify-personal
mcpc connect mcp.apify.com @apify-work --profile work

# Both sessions now work independently
mcpc @apify-personal tools-list  # Uses personal account
mcpc @apify-work tools-list      # Uses work account

# Re-authenticate existing profile (e.g., to refresh or change scopes)
mcpc login mcp.apify.com --profile work

# Delete "default" and "work" authentication profiles
mcpc logout mcp.apify.com
mcpc logout mcp.apify.com --profile work

Client registration approaches

When logging in, mcpc supports all three OAuth client registration approaches defined in the MCP authorization spec, picking the one the authorization server advertises in its OAuth metadata:

Approach	mcpc login flags
Pre-registration	--client-id (and optional --client-secret)
Client ID Metadata Documents (CIMD)	default (or --client-metadata-url <url>)
Dynamic Client Registration (DCR)	fallback (or force with --no-client-metadata-url)

mcpc ships with a hosted Client ID Metadata Document so every installation presents the same client identity to CIMD-capable authorization servers. When the authorization server advertises client_id_metadata_document_supported: true, the CIMD URL is used as the client_id; otherwise mcpc falls back to Dynamic Client Registration.

# Default: mcpc's hosted CIMD is used automatically (no flags needed).
mcpc login mcp.apify.com

# Pre-registered OAuth client (public or confidential) — skips CIMD.
mcpc login mcp.example.com --client-id <id> [--client-secret <secret>]

# Custom CIMD: override the default with your own hosted document.
mcpc login mcp.example.com --client-metadata-url https://example.com/my-client.json

# Disable CIMD: force Dynamic Client Registration even if the server supports CIMD.
mcpc login mcp.example.com --no-client-metadata-url

See the MCP authorization spec for details on each approach and the format of Client ID Metadata Documents.

Authentication precedence

When multiple authentication methods are available, mcpc uses this precedence order:

1. Command-line --header flag (highest priority) - Always used if provided
2. Saved authentication profiles - OAuth tokens from saved profile
3. Config file headers - Headers from --config file for the server
4. No authentication - Attempts unauthenticated connection

Note: --profile and --header "Authorization: ..." cannot be combined — they are mutually exclusive. Providing both will result in a clear error. Use one or the other.

mcpc automatically handles authentication based on what you specify:

When --header "Authorization: ..." is provided:

• The explicit header is always used, and OAuth profile auto-detection is skipped entirely
• This works even if a default profile exists for the server
• Cannot be combined with --profile (returns an error)

When --profile <name> is specified:

1. Profile exists for the server: Use its stored credentials
   • If authentication succeeds → Continue with command/session
   • If authentication fails (expired/invalid) → Fail with an error
2. Profile doesn't exist: Fail with an error

When --x402 is specified (without --profile):

• OAuth profile auto-detection is skipped, since x402 serves as the payment/auth mechanism
• If you also pass --profile, the specified profile is still used alongside x402

When --no-profile is specified:

• Skip all OAuth profile detection and connect anonymously
• Useful when a default profile exists but you want an unauthenticated session
• Can be combined with --header "Authorization: ..." for explicit bearer token without profile

When no flags are specified (default):

1. default profile exists for the server: Use its stored credentials
   • If authentication succeeds → Continue with command/session
   • If authentication fails (expired/invalid) → Fail with an error
2. default profile doesn't exist: Attempt unauthenticated connection
   • If server accepts (no auth required) → Continue without creating profile
   • If server rejects with 401 + WWW-Authenticate → Fail with an error

On failure, the error message includes instructions on how to login and save the profile, so you know what to do.

This flow ensures:

• Explicit CLI flags always take precedence over stored profiles
• Credentials are never silently mixed up (personal → work) or downgraded (authenticated → unauthenticated)
• You can mix authenticated sessions (with named profiles) and public access on the same server

Examples:

# With specific profile - always authenticated:
# - Uses 'work' if it exists
# - Fails if it doesn't exist
mcpc connect mcp.apify.com @apify-work --profile work

# Without profile - opportunistic authentication:
# - Uses 'default' if it exists
# - Tries unauthenticated if 'default' doesn't exist
# - Fails if the server requires authentication
mcpc connect mcp.apify.com @apify-personal

# Explicit bearer token - skips profile auto-detection:
mcpc connect mcp.apify.com @apify --header "Authorization: Bearer ${APIFY_TOKEN}"

# x402 payment - skips default profile auto-detection:
mcpc connect mcp.apify.com @apify --x402

# Anonymous - skips default profile even if it exists:
mcpc connect mcp.apify.com @apify-anon --no-profile

MCP proxy

For stronger isolation, mcpc can expose an MCP session under a new local proxy MCP server using the --proxy option. The proxy forwards all MCP requests to the upstream server but never exposes the original authentication tokens to the client. This is useful when you want to give someone or something MCP access without revealing your credentials. See also AI sandboxes.

# Human authenticates to a remote server
mcpc login mcp.apify.com

# Create authenticated session with proxy server on localhost:8080
mcpc connect mcp.apify.com @open-relay --proxy 8080

# Now any MCP client can connect to proxy like to a regular MCP server
# The client has NO access to the original OAuth tokens or HTTP headers
# Note: localhost/127.0.0.1 URLs default to http:// (no scheme needed)
mcpc connect localhost:8080 @sandboxed
mcpc @sandboxed tools-call search-actors keywords:="web scraper"

# Optionally protect proxy with bearer token for better security (stored in OS keychain)
mcpc connect mcp.apify.com @secure-relay --proxy 8081 --proxy-bearer-token secret123
# To use the proxy, caller needs to pass the bearer token in HTTP header
mcpc connect localhost:8081 @sandboxed2 --header "Authorization: Bearer secret123"

Proxy options for connect command:

Option	Description
--proxy [host:]port	Start proxy MCP server. Default host: 127.0.0.1 (localhost only)
--proxy-bearer-token <token>	Requires Authorization: Bearer <token> header to access the proxy MCP server

Security model:

• Localhost by default: --proxy 8080 binds to 127.0.0.1 only, preventing network access
• Tokens hidden: Original OAuth tokens and/or HTTP headers are never exposed to proxy clients
• Optional auth: Use --proxy-bearer-token to add another layer of security
• Explicit opt-in: Proxy only starts when --proxy flag is provided

Binding to network interfaces:

# Localhost only (default, most secure)
mcpc connect mcp.apify.com @relay --proxy 8080

# Bind to all interfaces (allows network access - use with caution!)
mcpc connect mcp.apify.com @relay --proxy 0.0.0.0:8080

# Bind to specific interface
mcpc connect mcp.apify.com @relay --proxy 192.168.1.100:8080

When listing sessions, proxy info is displayed prominently:

mcpc
# @relay → https://mcp.apify.com (HTTP, OAuth: default) [proxy: 127.0.0.1:8080]

AI agents

mcpc is designed for CLI-enabled AI agents like Claude Code or Codex CLI, supporting both interactive tool calling and code mode.

Tool calling mode - Agents call mcpc commands to dynamically explore and interact with MCP servers, using the default text output. This is similar to how MCP connectors in ChatGPT or Claude work, but CLI gives you more flexibility and longer operation timeouts.

# Discover available tools
mcpc @server tools-list

# Get tool schema
mcpc @server tools-get search

# Call a tool
mcpc @server tools-call search query:="hello world"

Code mode - Once agents understand the server's capabilities, they can write shell scripts that compose multiple mcpc commands with --json output. This can be more accurate and use fewer tokens than tool calling for complex workflows.

# AI-generated script using --json for structured data
mcpc --json @apify tools-call search-actors keywords:="scraper" \
  | jq '.content[0].text | fromjson | .items[0].id' \
  | xargs -I {} mcpc @apify tools-call get-actor actorId:="{}"

With schema validation, agents can ensure stability of integrations and faster failure recovery. Agents, make no harm!

See an example of an AI-generated shell script.

Scripting

Use --json for machine-readable output (stdout on success, stderr on error). JSON output of all MCP commands follows the MCP specification strictly.

# Chain tools across sessions
mcpc --json @apify tools-call search-actors keywords:="scraper" \
  | jq '.content[0].text | fromjson | .items[0].id' \
  | xargs -I {} mcpc @apify tools-call get-actor actorId:="{}"

# Batch operations
for tool in $(mcpc --json @server tools-list | jq -r '.[].name'); do
  mcpc --json @server tools-get "$tool" > "schemas/$tool.json"
done

For a complete example script, see docs/examples/company-lookup.sh.

Schema validation

The tools-get and tools-call commands support --schema to validate a tool's schema against an expected snapshot. This helps detect breaking changes early in scripts and CI:

# Save expected schema
mcpc --json @apify tools-get search-actors > expected.json

# Validate without calling (read-only check)
mcpc @apify tools-get search-actors --schema expected.json

# Validate before calling (fails if schema changed incompatibly)
mcpc @apify tools-call search-actors --schema expected.json keywords:="test"

Available schema validation modes (--schema-mode):

• compatible (default)
  • Input schema: new optional fields OK, required fields must have the same type.
  • Output schema: new fields OK, removed required fields cause error.
• strict - Both input and output schemas must match exactly, including all fields, types, and descriptions
• ignore - Skip validation completely (YOLO)

AI sandboxes

To ensure AI coding agents don't perform destructive actions or leak credentials, it's always a good idea to run them in a code sandbox with limited access to your resources.

The proxy MCP server feature provides a security boundary for AI agents:

1. Human creates authentication profile: mcpc login mcp.apify.com --profile ai-access
2. Human creates session: mcpc connect mcp.apify.com @ai-sandbox --profile ai-access --proxy 8080
3. AI runs inside a sandbox: If sandbox has access limited to localhost:8080, it can only interact with the MCP server through the @ai-sandbox session, without access to the original OAuth credentials, HTTP headers, or mcpc configuration.

This ensures AI agents operate only with pre-authorized credentials, preventing unauthorized access to MCP servers. The human controls which servers the AI can access and with what permissions (OAuth scopes).

IMPORTANT: Beware that MCP proxy will not make an insecure MCP server secure. Local stdio servers will still have access to your local system, and HTTP servers to provided auth credentials, and both can easily perform destructive actions or leak credentials on their own, or let MCP clients do such actions. Always use only trusted local and remote MCP servers and limit their access to the necessary minimum.

Agent skills

To help Claude Code use mcpc, you can install this Claude skill:

Agentic payments (x402)

⚠️ Experimental. This feature is under active development and may change.

mcpc has experimental support for the x402 payment protocol, which enables AI agents to autonomously pay for MCP tool calls using cryptocurrency. When an MCP server charges for a tool call (HTTP 402), mcpc automatically signs a USDC payment on the Base blockchain and retries the request — no human intervention needed.

This is entirely opt-in: existing functionality is unaffected unless you explicitly pass the --x402 flag.

How it works

1. Server returns HTTP 402 with a PAYMENT-REQUIRED header describing the price and payment details.
2. mcpc parses the header, signs an EIP-3009 TransferWithAuthorization using your local wallet.
3. mcpc retries the request with a PAYMENT-SIGNATURE header containing the signed payment.
4. The server verifies the signature and fulfills the request.

For tools that advertise pricing in their _meta.x402 metadata, mcpc can proactively sign payments on the first request, avoiding the 402 round-trip entirely.

Wallet setup

mcpc stores a single wallet in ~/.mcpc/wallets.json (file permissions 0600). You need to create or import a wallet before using x402 payments.

# Create a new wallet (generates a random private key)
mcpc x402 init

# Or import an existing wallet from a private key
mcpc x402 import <private-key>

# Show wallet address and creation date
mcpc x402 info

# Remove the wallet
mcpc x402 remove

After creating a wallet, fund it with USDC on Base (mainnet or Sepolia testnet) to enable payments.

Manual payment signing

You can manually sign a payment from a server's PAYMENT-REQUIRED header using x402 sign. This is useful for pre-signing payments or integrating with tools outside of mcpc.

# Sign a payment using the base64-encoded PAYMENT-REQUIRED header
mcpc x402 sign <base64-payment-required>

# Override the amount (in USD, e.g. 2.50 = $2.50)
mcpc x402 sign <base64-payment-required> --amount 2.50

# Override the expiry (in seconds from now)
mcpc x402 sign <base64-payment-required> --expiry 7200

# Combine overrides and use JSON output
mcpc x402 sign <base64-payment-required> --amount 1.00 --expiry 3600 --json

Options:

Option	Description
--amount <usd>	Override the payment amount in USD (e.g. 0.50 for $0.50)
--expiry <seconds>	Override the payment expiry in seconds from now (e.g. 3600)

The command outputs the signed PAYMENT-SIGNATURE header value and an MCP config snippet that can be used directly with other MCP clients.

Using x402 with MCP servers

Pass the --x402 flag when connecting to a session or running direct commands:

# Create a session with x402 payment support
mcpc connect mcp.apify.com @apify --x402

# The session now automatically handles 402 responses
mcpc @apify tools-call expensive-tool query:="hello"

# Restart a session with x402 enabled
mcpc @apify restart --x402

When --x402 is active, a fetch middleware wraps all HTTP requests to the MCP server. If any request returns HTTP 402, the middleware transparently signs and retries.

Supported networks

Network	Status
Base Mainnet	✅ Supported
Base Sepolia testnet	✅ Supported

MCP support

mcpc is built on the official MCP SDK for TypeScript and supports most MCP protocol features.

Transport

• stdio: Direct bidirectional JSON-RPC communication over stdio server from the config file.
• Streamable HTTP: Fully supported.
• HTTP with SSE (deprecated): Legacy mode, not supported.

Authorization

• Anonymous access
• HTTP header authorization
• OAuth 2.1

MCP session

The bridge process manages the full MCP session lifecycle:

• Performs initialization handshake (initialize → initialized)
• Negotiates protocol version and capabilities
• Fetches server-provided instructions
• Maintains persistent HTTP connections with bidirectional streaming, or stdio bidirectional pipe to subprocess
• Handles MCP-Protocol-Version and MCP-Session-Id headers automatically
• Handles multiple concurrent requests
• Recovers transparently from network disconnections and bridge process crashes

MCP feature support

Feature	Status
📖 Instructions	✅ Supported
🔧 Tools	✅ Supported
💬 Prompts	✅ Supported
📦 Resources	✅ Supported
📝 Logging	✅ Supported
🔔 Notifications	✅ Supported
📄 Pagination	✅ Supported
🏓 Ping	✅ Supported
⏳ Async tasks	✅ Supported
📁 Roots	🚧 Planned
❓ Elicitation	🚧 Planned
🔤 Completion	🚧 Planned
🤖 Sampling	❌ Not applicable (no LLM access)

Server instructions

MCP servers can provide instructions describing their capabilities and usage. These are displayed when you connect to a server or run the help command:

# Show server info, capabilities, and instructions (both commands behave the same)
mcpc @apify
mcpc @apify help

# JSON mode
mcpc @apify --json

In JSON mode, the resulting object adheres to InitializeResult object schema, and includes the _mcpc field with relevant server/session metadata.

{
  "_mcpc": {
    "sessionName": "@apify",
    "profileName": "default",
    "server": {
      "url": "https://mcp.apify.com"
    },
    "notifications": {
      "tools": { "listChangedAt": "2026-01-01T00:42:58.049Z" }
    }
  },
  "protocolVersion": "2025-06-18",
  "capabilities": {
    "logging": {},
    "prompts": {},
    "resources": {},
    "tools": { "listChanged": true }
  },
  "serverInfo": {
    "name": "apify-mcp-server",
    "version": "1.0.0"
  },
  "instructions": "Apify is the largest marketplace of tools for web scraping..."
}

Tools

List, inspect, and call server-provided tools:

# List available tools (only names and attributes - useful for dynamic discovery)
mcpc @apify tools-list

# List available tools (full details including input/output args and description)
mcpc @apify tools-list --full

# Get tool schema with full details
mcpc @apify tools-get search-actors

# Call a tool with arguments
mcpc @apify tools-call search-actors keywords:="web scraper"

# Pass complex JSON arguments
mcpc @apify tools-call create-task '{"name": "my-task", "options": {"memory": 1024}}'

# Load arguments from stdin
cat data.json | mcpc @apify tools-call bulk-import

Prompts

List and retrieve server-defined prompt templates:

# List available prompts
mcpc @apify prompts-list

# Get a prompt with arguments
mcpc @apify prompts-get analyze-website url:=https://example.com

Resources

Access server-provided data sources by URI:

# List available resources
mcpc @apify resources-list

# Read a resource
mcpc @apify resources-read "file:///config.json"

# Subscribe to resource changes (in shell mode)
mcpc @apify resources-subscribe "https://api.example.com/data"

# List resource templates
mcpc @apify resources-templates-list

List change notifications

When connected via a session, mcpc automatically handles list_changed notifications for tools, resources, and prompts. The bridge process tracks when each notification type was last received. In shell mode, notifications are displayed in real-time. The timestamps are available in JSON output of mcpc @session --json under the _mcpc.notifications field - see Server instructions.

Server logs

mcpc supports server logging settings (logging/setLevel) and log messages (notifications/message). Log messages are printed to bridge log or stderr, subject to verbosity level.

You can instruct MCP servers to adjust their logging level using the logging-set-level command:

# Set server log level to debug for detailed output
mcpc @apify logging-set-level debug

# Reduce server logging to only errors
mcpc @apify logging-set-level error

Note that this sets the logging level on the server side. The actual log output depends on the server's implementation.

Pagination

MCP servers may return paginated results for list operations (tools-list, resources-list, prompts-list, resources-templates-list). mcpc handles this automatically and always fetches all available pages using the nextCursor token - you always get the complete list without manual iteration. Keep it simple.

Ping

Sessions automatically send periodic pings to keep the connection alive and detect failures early. Send a ping to check if a server connection is alive:

# Ping a session and measure round-trip time
mcpc @apify ping
mcpc @apify ping --json

Async tasks

MCP servers can execute tools as async tasks that run in the background and report progress. mcpc supports the full task lifecycle:

# Call a tool as a task (waits for completion, shows progress spinner)
mcpc @apify tools-call long-running-job input:="data" --task

# Start a task and return immediately with the task ID
mcpc @apify tools-call long-running-job input:="data" --detach

# List active tasks
mcpc @apify tasks-list

# Check task status
mcpc @apify tasks-get <taskId>

# Get the task result (blocks until the task reaches a terminal state)
mcpc @apify tasks-result <taskId>

# Cancel a running task
mcpc @apify tasks-cancel <taskId>

With --task, the CLI shows a progress spinner with elapsed time, server status messages, and progress notifications. Press ESC during execution to detach and get the task ID for later retrieval. With --detach, the task starts and returns the task ID immediately. Use tasks-result <taskId> to fetch the final CallToolResult payload once the task completes.

tools-list and tools-get show task support annotations per tool: [task:optional], [task:required], or [task:forbidden].

Configuration

You can configure mcpc using a config file, environment variables, or command-line flags.

Precedence (highest to lowest):

1. Command-line flags (including --config option)
2. Environment variables
3. Built-in defaults

MCP server config file

mcpc supports the "standard" MCP server JSON config file, compatible with Claude Desktop, VS Code, and other MCP clients. Use the file:entry syntax to reference a server from a config file:

# Open a session to a server specified in the Visual Studio Code config
mcpc connect .vscode/mcp.json:apify @my-apify
mcpc @my-apify tools-list

Example MCP config JSON file:

{
  "mcpServers": {
    "apify": {
      "url": "https://mcp.apify.com",
      "headers": {
        "Authorization": "Bearer ${APIFY_TOKEN}"
      }
    },
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-filesystem", "/tmp"],
      "env": {
        "DEBUG": "mcp:*"
      }
    },
    "local-package": {
      "command": "node",
      "args": ["/path/to/server.js"]
    }
  }
}

Server configuration properties:

For Streamable HTTP servers:

• url (required) - MCP server endpoint URL
• headers (optional) - HTTP headers to include with requests
• timeout (optional) - Request timeout in seconds

For stdio servers:

• command (required) - Command to execute (e.g., node, npx, python)
• args (optional) - Array of command arguments
• env (optional) - Environment variables for the process

Note: Stdio servers inherit only a minimal env whitelist from the shell (PATH, HOME, SHELL, …). Other vars — NODE_EXTRA_CA_CERTS, HTTPS_PROXY, SSL_CERT_FILE, etc. — must be forwarded explicitly via the env block using ${VAR_NAME}. Anything the server writes to stderr is captured to ~/.mcpc/logs/bridge-<session>.log with a [server stderr] prefix, and the tail is appended to the error message if mcpc connect fails, so you can see why a stdio server failed to start.

Using servers from config file:

Reference servers by their name using the file:entry syntax:

# Create a named session from a server in the config
mcpc connect .vscode/mcp.json:filesystem @fs
mcpc @fs tools-list
mcpc @fs tools-call search

Environment variable substitution:

Config files support environment variable substitution using ${VAR_NAME} syntax:

{
  "mcpServers": {
    "secure-server": {
      "url": "https://mcp.apify.com",
      "headers": {
        "Authorization": "Bearer ${APIFY_TOKEN}",
        "X-User-ID": "${USER_ID}"
      }
    }
  }
}

Saved state

mcpc saves its state to ~/.mcpc/ directory (unless overridden by MCPC_HOME_DIR), in the following files:

• ~/.mcpc/sessions.json - Active sessions with references to authentication profiles (file-locked for concurrent access)
• ~/.mcpc/profiles.json - Authentication profiles (OAuth metadata, scopes, expiry)
• ~/.mcpc/wallets.json - x402 wallet data (file permissions 0600)
• ~/.mcpc/bridges/ - Unix domain socket files for each bridge process
• ~/.mcpc/logs/bridge-*.log - Log files for each bridge process
• OS keychain - Sensitive credentials (OAuth tokens, bearer tokens, client secrets)

Environment variables

• MCPC_HOME_DIR - Directory for session and authentication profiles data (default is ~/.mcpc)
• MCPC_VERBOSE - Enable verbose logging (set to 1, true, or yes, case-insensitive)
• MCPC_JSON - Enable JSON output (set to 1, true, or yes, case-insensitive)
• HTTPS_PROXY / https_proxy / HTTP_PROXY / http_proxy - Proxy URL for outbound connections (e.g. http://proxy.example.com:8080); HTTPS_PROXY takes precedence
• NO_PROXY / no_proxy - Comma-separated list of hostnames/IPs to bypass the proxy (e.g. localhost,127.0.0.1)

Cleanup

You can clean up the mcpc state and data using the clean command:

# Safe non-destructive cleanup: remove expired sessions, delete old orphaned logs
mcpc clean

# Clean specific resources
mcpc clean sessions    # Kill bridges, delete all sessions
mcpc clean profiles    # Delete all authentication profiles
mcpc clean logs        # Delete all log files

# Nuclear option: remove everything
mcpc clean all         # Delete all sessions, profiles, logs, and sockets

Security

mcpc follows MCP security best practices. MCP enables arbitrary tool execution and data access - treat servers like you treat shells:

• Use least-privilege tokens/headers
• Only use trusted servers!
• Audit tools before running them

Credential protection

What	How
OAuth tokens	Stored in OS keychain, never on disk
HTTP headers	Stored in OS keychain per-session
Bridge credentials	Passed via Unix socket IPC, kept in memory only
Process arguments	No secrets visible in ps aux
x402 private key	Stored in wallets.json (0600 permissions)
Config files	Contain only metadata, never tokens
File permissions	0600 (user-only) for all config files

Network security

• HTTPS enforced for remote servers (auto-upgraded from HTTP)
• OAuth callback binds to 127.0.0.1 only
• Credentials never logged, even in verbose mode

AI security

See AI sandboxes for details.

Errors

mcpc provides clear error messages for common issues:

• Connection failures: Displays transport-level errors with retry suggestions
• Session timeouts: Automatically attempts to reconnect or prompts for session recreation
• Invalid commands: Shows available commands and correct syntax
• Tool execution errors: Returns server error messages with context
• Bridge crashes: Detects and cleans up orphaned processes, offers restart

Exit codes

• 0 - Success
• 1 - Client error (invalid arguments, command not found, etc.)
• 2 - Server error (tool execution failed, resource not found, etc.)
• 3 - Network error (connection failed, timeout, etc.)
• 4 - Authentication error (invalid credentials, forbidden, etc.)

Verbose mode

To see what's happening, enable detailed logging with --verbose.

mcpc --verbose @apify tools-list

This causes mcpc to print detailed debug messages to stderr.

Logs

The background bridge processes log to ~/.mcpc/logs/bridge-@<session>.log. The main mcpc process doesn't save log files, but supports verbose mode. mcpc automatically rotates log files: keep last 10MB per session, max 5 files.

Troubleshooting

"Cannot connect to bridge"

• Bridge may have crashed. Try: mcpc @<session-name> tools-list to restart the bridge
• Check bridge is running: ps aux | grep -e 'mcpc-bridge' -e '[m]cpc/dist/bridge'
• Check socket exists: ls ~/.mcpc/bridges/

"Session not found"

• List existing sessions: mcpc
• Create new session if expired: mcpc @<session-name> close and mcpc connect <server> @<session-name>

"Authentication failed"

• List saved OAuth profiles: mcpc
• Re-authenticate: mcpc login <server> [--profile <name>]
• For bearer tokens: provide --header "Authorization: Bearer ${TOKEN}" again

Development

The initial version of mcpc was developed and launched by Jan Curn of Apify with the help of Claude Code, during late nights over Christmas 2025 in North Beach, San Francisco.

See CONTRIBUTING for development setup, architecture overview, and contribution guidelines.

Related work

MCP CLI clients

Tool	Lang	Stars	Contrib / Commits	Active	Tools	Resources	Prompts	Tasks	Code mode	Sessions	OAuth	Stdio	HTTP	Tool search	x402	LLM
apify/mcpc	TS	~420	7 / ~510	✅	✅	✅	✅	✅	✅	✅	✅	✅	✅	✅	✅	—
steipete/mcporter	TS	~3.5k	24 / ~570	✅	✅	—	—	—	✅	✅	✅	✅	✅	—	—	—
IBM/mcp-cli	Python	~1.9k	22 / ~790	✅	✅	✅	✅	—	✅	✅	✅	✅	✅	—	—	✅
knowsuchagency/mcp2cli	Python	~1.8k	5 / ~76	✅	✅	✅	✅	—	✅	✅	✅	✅	✅	✅	—	—
f/mcptools	Go	~1.5k	15 / ~170	⚠️	✅	✅	✅	—	✅	—	—	✅	✅	—	—	—
philschmid/mcp-cli	TS	~1.1k	2 / ~30	✅	✅	—	—	—	✅	✅	—	✅	✅	✅	—	—
adhikasp/mcp-client-cli	Python	~670	6 / ~110	⚠️	✅	✅	✅	—	—	—	—	✅	—	—	—	✅
thellimist/clihub	Go	~640	1 / ~60	✅	✅	—	—	—	—	—	✅	✅	✅	✅	—	—
wong2/mcp-cli	JS	~430	4 / ~63	⚠️	✅	✅	✅	—	—	—	✅	—	✅	—	—	—
mcpshim/mcpshim	Go	~54	1 / ~13	✅	✅	—	—	—	✅	✅	✅	—	✅	✅	—	—
evantahler/mcpx	TS	~28	1 / ~64	✅	✅	✅	✅	✅	✅	—	✅	✅	✅	✅	—	—
EstebanForge/mcp-cli-ent	Go	~15	~2 / ~46	✅	✅	—	—	—	✅	✅	—	✅	✅	✅	—	—

Legend: ✅ = supported, ⚠️ = stale (no commits in 3+ months), Contrib / Commits = contributors / total commits, Tasks = async tasks, x402 = x402 payment protocol support, LLM = requires/uses an LLM.

Notes:

• thellimist/clihub is a code generator that compiles MCP tools into standalone CLI binaries, rather than a runtime client (HN discussion).
• knowsuchagency/mcp2cli also supports OpenAPI specs directly and uses a custom TOON encoding for token-efficient tool schemas.
• IBM/mcp-cli and mcp-client-cli integrate an LLM (Ollama, OpenAI, etc.) for chat-style interaction, while the other tools are pure CLI clients.

Code mode and dynamic tool discovery

These resources describe the "code mode" pattern (replacing many tool definitions with search + execute) and dynamic tool discovery:

• Code mode - Anthropic's blog post on code execution with MCP
• Code mode at Cloudflare - Cloudflare's implementation of the code mode pattern
• Advanced tool use - Anthropic's engineering post on tool search
  • Claude tool search - Claude platform docs
• Dynamic context discovery - Cursor's approach to dynamic tool discovery
• cmcp (~27 stars, Rust) - MCP proxy aggregating servers behind search() + execute()
• cloudflare-mcp (~124 stars, TS) - MCP server for the Cloudflare API using code mode
• infinite-mcp (Python) - Meta-MCP server that exposes 1000+ pre-indexed MCP servers via semantic search and dynamic tool discovery

Other

• mcpGraph - MCP server that orchestrates directed graphs of MCP tool calls

License

Apache-2.0 - see LICENSE for details.