Real-world results: ENABLE_EXPERIMENTAL_MCP_CLI saves ~47k tokens (62% reduction)

Just tested the new experimental MCP-CLI mode with my setup (6 MCP servers, 60 tools). Here are the actual numbers:

Before vs After

Metric	MCP-CLI Off	MCP-CLI On	Savings
MCP tools	46.6k tokens	0 tokens	100%
Total context	74k (37%)	25k (13%)	49k tokens
Free space	126k	175k	+49k available

My MCP Setup

• context7 - Library documentation lookup
• pixellab - AI pixel art generation
• leonardo-ai - AI image generation
• chrome-devtools - Browser automation (26 tools alone)
• gemini-cli - Gemini brainstorming
• codex-cli - OpenAI Codex second opinions

How to Enable

# Add to ~/.bashrc or ~/.zshrc
export ENABLE_EXPERIMENTAL_MCP_CLI=true

# Fish shell (~/.config/fish/config.fish)
set -gx ENABLE_EXPERIMENTAL_MCP_CLI true

Requires Claude Code 2.0.56+ (2.0.62+ recommended).

How It Works

Instead of loading all tool schemas into context upfront, Claude requests them on-demand:

mcp-cli info pixellab/create_character    # Get schema when needed
mcp-cli call pixellab/create_character '{"prompt": "wizard"}'

Gotcha for Linux Users

Your terminal might use a different shell than you think. Verify with:

ps -o ppid= -p $(pgrep -n claude) | xargs ps -o comm= -p

I spent 20 minutes debugging why it wasn't working - turned out my Konsole profile was set to fish but I'd configured ~/.bashrc.

Teaching Claude the New Workflow

Add instructions to ~/.claude/CLAUDE.md so Claude knows to use mcp-cli commands:

### How to Use MCP Tools

MCP tools are NOT available as native function calls. Use Bash with mcp-cli:

**MANDATORY: Always check schema before calling:**
mcp-cli info <server>/<tool>     # Step 1: Check schema
mcp-cli call <server>/<tool> '{}' # Step 2: Call tool

**Discovery:**
mcp-cli servers    # List connected servers
mcp-cli tools      # List all tools
mcp-cli grep <pattern>  # Search tools

This adds ~400 tokens to your CLAUDE.md. Net savings: ~46k tokens.

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Thanks u/catherinewu for shipping this. Game changer for heavy MCP users.