mcp-cli

A lightweight, Bun-based CLI for interacting with MCP (Model Context Protocol) servers.

Features

🪶 Lightweight - Minimal dependencies, fast startup
📦 Single Binary - Compile to standalone executable via bun build --compile
🔧 Shell-Friendly - JSON output for call, pipes with jq, chaining support
🤖 Agent-Optimized - Designed for AI coding agents (Gemini CLI, Claude Code, etc.)
🔌 Universal - Supports both stdio and HTTP MCP servers
⚡ Connection Pooling - Lazy-spawn daemon keeps connections warm (60s idle timeout)
� Tool Filtering - Allow/disable specific tools per server via config
📋 Server Instructions - Display MCP server instructions in output
�💡 Actionable Errors - Structured error messages with available servers and recovery suggestions

Quick Start

1. Installation

curl -fsSL https://raw.githubusercontent.com/philschmid/mcp-cli/main/install.sh | bash

or

# requires bun install
bun install -g https://github.com/philschmid/mcp-cli

2. Create a config file

Create mcp_servers.json in your current directory or ~/.config/mcp/:

{
"mcpServers": {
"filesystem": {
"command": "npx",
"args": [
"-y",
"@modelcontextprotocol/server-filesystem",
"."
]
},
"deepwiki": {
"url": "https://mcp.deepwiki.com/mcp"
}
}
}

3. Discover available tools

# List all servers and tools
mcp-cli
# With descriptions
mcp-cli -d

4. Call a tool

# View tool schema first
mcp-cli info filesystem read_file
# Call the tool
mcp-cli call filesystem read_file '{"path": "./README.md"}'

Usage

mcp-cli [options] List all servers and tools
mcp-cli [options] info <server> Show server tools and parameters
mcp-cli [options] info <server> <tool> Show tool schema
mcp-cli [options] grep <pattern> Search tools by glob pattern
mcp-cli [options] call <server> <tool> Call tool (reads JSON from stdin if no args)
mcp-cli [options] call <server> <tool> <json> Call tool with JSON arguments

Both formats work:info <server> <tool> or info <server>/<tool>

Tip

Add -d to any command to include descriptions.

Options

Option	Description
`-h, --help`	Show help message
`-v, --version`	Show version number
`-d, --with-descriptions`	Include tool descriptions
`-c, --config <path>`	Path to config file

Output

Stream	Content
stdout	Tool results and human-readable info
stderr	Errors and diagnostics

Commands

List Servers

# Basic listing
$ mcp-cli
github
• search_repositories
• get_file_contents
• create_or_update_file
filesystem
• read_file
• write_file
• list_directory
# With descriptions
$ mcp-cli --with-descriptions
github
• search_repositories - Search for GitHub repositories
• get_file_contents - Get contents of a file or directory
filesystem
• read_file - Read the contents of a file
• write_file - Write content to a file

Search Tools

# Find file-related tools across all servers
$ mcp-cli grep "*file*"
github/get_file_contents
github/create_or_update_file
filesystem/read_file
filesystem/write_file
# Search with descriptions
$ mcp-cli grep "*search*" -d
github/search_repositories - Search for GitHub repositories

View Server Details

$ mcp-cli info github
Server: github
Transport: stdio
Command: npx -y @modelcontextprotocol/server-github
Tools (12):
search_repositories
Search for GitHub repositories
Parameters:
• query (string, required) - Search query
• page (number, optional) - Page number
...

View Tool Schema

# Both formats work:
$ mcp-cli info github search_repositories
$ mcp-cli info github/search_repositories
Tool: search_repositories
Server: github
Description:
Search for GitHub repositories
Input Schema:
{
"type": "object",
"properties": {
"query": { "type": "string", "description": "Search query" },
"page": { "type": "number" }
},
"required": ["query"]
}

Call a Tool

# With inline JSON
$ mcp-cli call github search_repositories '{"query": "mcp server", "per_page": 5}'# JSON output is default for call command
$ mcp-cli call github search_repositories '{"query": "mcp"}'| jq '.content[0].text'# Read JSON from stdin (no '-' needed!)
$ echo'{"path": "./README.md"}'| mcp-cli call filesystem read_file

Complex Commands

For JSON arguments containing single quotes, special characters, or long text, use stdin to avoid shell escaping issues:

# Using a heredoc (no '-' needed with call subcommand)
mcp-cli call server tool <<EOF{"content": "Text with 'single quotes' and \"double quotes\""}EOF# From a file
cat args.json | mcp-cli call server tool
# Using jq to build complex JSON
jq -n '{query: "mcp", filters: ["active", "starred"]}'| mcp-cli call github search

Why stdin? Shell interpretation of {}, quotes, and special characters requires careful escaping. Stdin bypasses shell parsing entirely.

Advanced Chaining Examples

Chain multiple MCP calls together using pipes and shell tools:

# 1. Search and read: Find files matching pattern, then read the first one
mcp-cli call filesystem search_files '{"path": "src/", "pattern": "*.ts"}' \
| jq -r '.content[0].text | split("\n")[0]' \
| xargs -I {} mcp-cli call filesystem read_file '{"path": "{}"}'# 2. Process multiple results: Read all matching files
mcp-cli call filesystem search_files '{"path": ".", "pattern": "*.md"}' \
| jq -r '.content[0].text | split("\n")[]' \
|whileread file;doecho"=== $file ==="
mcp-cli call filesystem read_file "{\"path\": \"$file\"}"| jq -r '.content[0].text'done# 3. Extract and transform: Get repo info, extract URLs
mcp-cli call github search_repositories '{"query": "mcp server", "per_page": 5}' \
| jq -r '.content[0].text | fromjson | .items[].html_url'# 4. Conditional execution: Check file exists before reading
mcp-cli call filesystem list_directory '{"path": "."}' \
| jq -e '.content[0].text | contains("README.md")' \
&& mcp-cli call filesystem read_file '{"path": "./README.md"}'# 5. Save output to file
mcp-cli call github get_file_contents '{"owner": "user", "repo": "project", "path": "src/main.ts"}' \
| jq -r '.content[0].text'> main.ts
# 6. Error handling in scriptsif result=$(mcp-cli call filesystem read_file '{"path": "./config.json"}'2>/dev/null);thenecho"$result"| jq '.content[0].text | fromjson'elseecho"File not found, using defaults"fi# 7. Aggregate results from multiple servers
{
mcp-cli call github search_repositories '{"query": "mcp", "per_page": 3}'
mcp-cli call filesystem list_directory '{"path": "./src"}'
} | jq -s '.'

Tips for chaining:

Use jq -r for raw output (no quotes)
Use jq -e for conditional checks (exit code 1 if false)
Use 2>/dev/null to suppress errors when testing
Use | jq -s '.' to combine multiple JSON outputs

Configuration

Config File Format

The CLI uses mcp_servers.json, compatible with Claude Desktop, Gemini or VS Code:

{
"mcpServers": {
"local-server": {
"command": "node",
"args": ["./server.js"],
"env": {
"API_KEY": "${API_KEY}"
},
"cwd": "/path/to/directory"
},
"remote-server": {
"url": "https://mcp.example.com",
"headers": {
"Authorization": "Bearer ${TOKEN}"
}
}
}
}

SSE Transport (Legacy)

For servers using the deprecated SSE transport protocol, add "type": "sse" to the configuration:

{
"mcpServers": {
"legacy-server": {
"url": "http://localhost:8000",
"type": "sse"
}
}
}

Note

SSE transport is deprecated. New servers should use Streamable HTTP transport.

Environment Variable Substitution: Use ${VAR_NAME} syntax anywhere in the config. Values are substituted at load time. By default, missing environment variables cause an error with a clear message. Set MCP_STRICT_ENV=false to use empty values instead (with a warning).

Tool Filtering

Restrict which tools are available from a server using allowedTools and disabledTools:

{
"mcpServers": {
"filesystem": {
"command": "npx",
"args": ["-y", "@modelcontextprotocol/server-filesystem", "."],
"allowedTools": ["read_file", "list_directory"],
"disabledTools": ["delete_file"]
}
}
}

Rules:

allowedTools: Only tools matching these patterns are available (supports glob: *, ?)
disabledTools: Tools matching these patterns are excluded
disabledTools takes precedence over allowedTools
Filtering applies globally to all CLI operations (info, grep, call)

Examples:

// Only allow read operations"allowedTools": ["read_*", "list_*", "search_*"]
// Allow all except destructive operations"disabledTools": ["delete_*", "write_*", "create_*"]
// Combine: allow file operations but disable delete"allowedTools": ["*file*"],
"disabledTools": ["delete_file"]

Config Resolution

The CLI searches for configuration in this order:

MCP_CONFIG_PATH environment variable
-c/--config command line argument
./mcp_servers.json (current directory)
~/.mcp_servers.json
~/.config/mcp/mcp_servers.json

Environment Variables

Variable	Description	Default
`MCP_CONFIG_PATH`	Path to config file	(none)
`MCP_DEBUG`	Enable debug output	`false`
`MCP_TIMEOUT`	Request timeout (seconds)	`1800` (30 min)
`MCP_CONCURRENCY`	Servers processed in parallel (not a limit on total)	`5`
`MCP_MAX_RETRIES`	Retry attempts for transient errors (0 = disable)	`3`
`MCP_RETRY_DELAY`	Base retry delay (milliseconds)	`1000`
`MCP_STRICT_ENV`	Error on missing `${VAR}` in config	`true`
`MCP_NO_DAEMON`	Disable connection caching (force fresh connections)	`false`
`MCP_DAEMON_TIMEOUT`	Idle timeout for cached connections (seconds)	`60`

Using with AI Agents

mcp-cli is designed to give AI coding agents access to MCP (Model Context Protocol) servers. MCP enables AI models to interact with external tools, APIs, and data sources through a standardized protocol.

Why MCP + CLI?

Traditional MCP integration loads full tool schemas into the AI's context window, consuming thousands of tokens. The CLI approach:

On-demand loading: Only fetch schemas when needed
Token efficient: Minimal context overhead
Shell composable: Chain with jq, pipes, and scripts
Scriptable: AI can write shell scripts for complex workflows

Option 1: System Prompt Integration

Add this to your AI agent's system prompt for direct CLI access:

## MCP Servers
You have access to MCP servers via the `mcp-cli` CLI.
Commands:
```bash
mcp-cli info # List all servers
mcp-cli info <server> # Show server tools mcp-cli info <server> <tool> # Get tool schema
mcp-cli grep "<pattern>" # Search tools
mcp-cli call <server> <tool> # Call tool (stdin auto-detected)
mcp-cli call <server> <tool> '{}' # Call with JSON args
```
**Both formats work:** `info <server> <tool>` or `info <server>/<tool>`
Workflow:
1. **Discover**: `mcp-cli info` to see available servers
2. **Inspect**: `mcp-cli info <server> <tool>` to get the schema
3. **Execute**: `mcp-cli call <server> <tool> '{}'` with arguments
### Examples
```bash
# Call with inline JSON
mcp-cli call github search_repositories '{"query": "mcp server"}'
# Pipe from stdin (no '-' needed)
echo '{"path": "./file"}' | mcp-cli call filesystem read_file
# Heredoc for complex JSON
mcp-cli call server tool <<EOF
{"content": "Text with 'quotes'"}
EOF
```
### Common Errors
| Wrong | Error | Fix |
|-------|-------|-----|
| `mcp-cli server tool` | AMBIGUOUS | Use `call server tool` |
| `mcp-cli run server tool` | UNKNOWN_SUBCOMMAND | Use `call` |
| `mcp-cli list` | UNKNOWN_SUBCOMMAND | Use `info` |

Option 2: Agents Skill

For Code Agents that support Agents Skills, like Gemini CLI, OpenCode or Claude Code. you can use the mcp-cli skill to interface with MCP servers. The Skill is available at SKILL.md

Create mcp-cli/SKILL.md in your skills directory.

Architecture

Connection Pooling (Daemon)

By default, the CLI uses lazy-spawn connection pooling to avoid repeated MCP server startup latency:

┌────────────────────────────────────────────────────────────────────┐
│ First CLI Call │
│ $ mcp-cli info server │
└────────────────────────────────────────────────────────────────────┘
│
▼
┌────────────────────────────────────────────────────────────────────┐
│ Check: /tmp/mcp-cli-{uid}/server.sock exists? │
└────────────────────────────────────────────────────────────────────┘
│ │
│ NO │ YES
▼ ▼
┌─────────────────────────┐ ┌───────────────────────────────────┐
│ Fork background daemon │ │ Connect to existing socket │
│ ├─ Connect to MCP server│ │ ├─ Send request via IPC │
│ ├─ Create Unix socket │ │ ├─ Receive response │
│ └─ Start 60s idle timer │ │ └─ Daemon resets idle timer │
└─────────────────────────┘ └───────────────────────────────────┘
│ │
└────────────────┬───────────────────┘
▼
┌────────────────────────────────────────────────────────────────────┐
│ On idle timeout (60s): Daemon self-terminates, cleans up files │
└────────────────────────────────────────────────────────────────────┘

Key features:

Automatic: No manual start/stop needed
Per-server: Each MCP server gets its own daemon
Stale detection: Config changes trigger re-spawn
Fast fallback: 5s spawn timeout, then direct connection

Control via environment:

MCP_NO_DAEMON=1 mcp-cli info # Force fresh connection
MCP_DAEMON_TIMEOUT=120 mcp-cli # 2 minute idle timeout
MCP_DEBUG=1 mcp-cli info # See daemon debug output

Connection Model (Direct)

When daemon is disabled (MCP_NO_DAEMON=1), the CLI uses a lazy, on-demand connection strategy. Server connections are only established when needed and closed immediately after use.

┌─────────────────────────────────────────────────────────────────┐
│ USER REQUEST │
└─────────────────────────────────────────────────────────────────┘
│
┌─────────────────┼─────────────────┐
│ │ │
▼ ▼ ▼
┌─────────────────┐ ┌─────────────────┐ ┌─────────────────┐
│ mcp-cli info │ │ mcp-cli grep │ │ mcp-cli call │
│ (list all) │ │ "*pattern*" │ │ server tool {} │
└─────────────────┘ └─────────────────┘ └─────────────────┘
│ │ │
▼ ▼ ▼
┌─────────────────┐ ┌─────────────────┐ ┌─────────────────┐
│ Connect to ALL │ │ Connect to ALL │ │ Connect to ONE │
│ servers (N) │ │ servers (N) │ │ server only │
└─────────────────┘ └─────────────────┘ └─────────────────┘
│ │ │
▼ ▼ ▼
List tools Search tools Execute tool
│ │ │
▼ ▼ ▼
┌─────────────────────────────────────────────────────────────┐
│ CLOSE CONNECTIONS │
└─────────────────────────────────────────────────────────────┘

When are servers connected?

Command	Servers Connected
`mcp-cli info`	All N servers in parallel
`mcp-cli grep "pattern"`	All N servers in parallel
`mcp-cli info <server>`	Only the specified server
`mcp-cli info <server> <tool>`	Only the specified server
`mcp-cli call <server> <tool> '{}'`	Only the specified server

Error Handling & Retry

The CLI includes automatic retry with exponential backoff for transient failures.

Transient errors (auto-retried):

Network: ECONNREFUSED, ETIMEDOUT, ECONNRESET
HTTP: 502, 503, 504, 429

Non-transient errors (fail immediately):

Config: Invalid JSON, missing fields
Auth: 401, 403
Tool: Validation errors, not found

Development

Prerequisites

Bun >= 1.0.0

Setup

bun install https://github.com/philschmid/mcp-cli

Commands

# Run in development
bun run dev
# Type checking
bun run typecheck
# Linting
bun run lint
bun run lint:fix
# Run all tests (unit + integration)
bun test# Run only unit tests (fast)
bun test tests/config.test.ts tests/output.test.ts tests/client.test.ts
# Run integration tests (requires MCP server, ~35s)
bun test tests/integration/
# Build single executable
bun run build
# Build for all platforms
bun run build:all

Local Testing

Test the CLI locally without compiling by using bun link:

# Link the package globally (run once)
bun link
# Now you can use 'mcp-cli' anywhere
mcp-cli --help
mcp-cli call filesystem read_file '{"path": "./README.md"}'# Or run directly during development
bun run dev --help
bun run dev info filesystem

To unlink when done:

bun unlink

Releasing

Releases are automated via GitHub Actions. Use the release script:

./scripts/release.sh 0.2.0

Error Messages

All errors include actionable recovery suggestions, optimized for both humans and AI agents:

Error [AMBIGUOUS_COMMAND]: Ambiguous command: did you mean to call a tool or view info?
Details: Received: mcp-cli filesystem read_file
Suggestion: Use 'mcp-cli call filesystem read_file' to execute, or 'mcp-cli info filesystem read_file' to view schema
Error [UNKNOWN_SUBCOMMAND]: Unknown subcommand: "run"
Details: Valid subcommands: info, grep, call
Suggestion: Did you mean 'mcp-cli call'?
Error [SERVER_NOT_FOUND]: Server "github" not found in config
Details: Available servers: filesystem, sqlite
Suggestion: Use one of: mcp-cli info filesystem, mcp-cli info sqlite
Error [TOOL_NOT_FOUND]: Tool "search" not found in server "filesystem"
Details: Available tools: read_file, write_file, list_directory (+5 more)
Suggestion: Run 'mcp-cli info filesystem' to see all available tools
Error [INVALID_JSON_ARGUMENTS]: Invalid JSON in tool arguments
Details: Parse error: Unexpected identifier "test"
Suggestion: Arguments must be valid JSON. Use single quotes: '{"key": "value"}'

License

MIT License - see LICENSE for details.

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

Name		Name	Last commit message	Last commit date
.github/workflows		.github/workflows
scripts		scripts
src		src
tests		tests
.gitignore		.gitignore
CHANGELOG.md		CHANGELOG.md
LICENSE		LICENSE
README.md		README.md
SKILL.md		SKILL.md
biome.json		biome.json
bun.lock		bun.lock
comparison.jpeg		comparison.jpeg
install.sh		install.sh
mcp_servers.json		mcp_servers.json
package.json		package.json
tsconfig.json		tsconfig.json

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mcp-cli

Features

Quick Start

1. Installation

2. Create a config file

3. Discover available tools

4. Call a tool

Usage

Options

Output

Commands

List Servers

Search Tools

View Server Details

View Tool Schema

Call a Tool

Complex Commands

Advanced Chaining Examples

Configuration

Config File Format

SSE Transport (Legacy)

Tool Filtering

Config Resolution

Environment Variables

Using with AI Agents

Why MCP + CLI?

Option 1: System Prompt Integration

Option 2: Agents Skill

Architecture

Connection Pooling (Daemon)

Connection Model (Direct)

Error Handling & Retry

Development

Prerequisites

Setup

Commands

Local Testing

Releasing

Error Messages

License

Contributing

About

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Releases

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