pi-mcp-adapter

Pi MCP Adapter

Use MCP servers with Pi without burning your context window.

https://github.com/user-attachments/assets/4b7c66ff-e27e-4639-b195-22c3db406a5a

Why This Exists

Mario wrote about why you might not need MCP. The problem: tool definitions are verbose. A single MCP server can burn 10k+ tokens, and you're paying that cost whether you use those tools or not. Connect a few servers and you've burned half your context window before the conversation starts.

His take: skip MCP entirely, write simple CLI tools instead.

But the MCP ecosystem has useful stuff - databases, browsers, APIs. This adapter gives you access without the bloat. One proxy tool (~200 tokens) instead of hundreds. The agent discovers what it needs on-demand. Servers only start when you actually use them.

pi-mcp-adapter vs Pi's built-in MCP

Since then, Pi 0.99 added MCP support of its own, which also keeps tool definitions out of context. Installing the adapter replaces it in Pi sessions. What you get by switching:

• Install many servers without paying for idle ones. The built-in starts every enabled server in every Pi session and keeps it running until the session ends. By default, the adapter starts a server when the model first calls it and stops it after 10 idle minutes.
• Fewer tokens on everyday calls. By default, the built-in runs every MCP call as a codemode script, even a single lookup. The adapter's scripts are off by default, so a lookup is one small JSON call to the mcp tool, which cost 10–33% less in our tests. For bulk work across many records, turn scripts on with settings.scriptMode; then it costs about the same as codemode.
• More servers work fully. Servers can ask you questions through forms, show interactive UIs, and offer prompt templates as slash commands. The built-in doesn't handle these.
• Find tools by what you mean. The built-in's tool search only matches words. With a System One key, the adapter can also rank tools by meaning: in a test of 12 everyday requests across 95 tools, it put the right tool first in 10 of 11, where word search did in 5.
• Sign-in tokens go in your OS keychain by default (an encrypted file is opt-in), not in a plain JSON file under ~/.pi/agent.
• Adding servers is easier. Give the agent a server's URL and it installs it and checks its tools in the same session, opening sign-in first if the server needs it, with no shell command or /reload. Servers already configured in Cursor, Claude Code, Codex, or VS Code can be imported with /mcp-adapter setup, which also adds presets such as Figma and GitHub.

The built-in has two things the adapter doesn't: Pi's permission extensions see each MCP call as its own tool call without changes, and it sends roots (the session directory) to servers. Pi's codemode works with both.

	Pi's built-in MCP	pi-mcp-adapter
Servers running	Every enabled server, for the whole session	Only servers in use; each stops after 10 idle minutes
Server memory (100 installed, 3 in use)	7.0 GB at start, 5.9 GB after 15 minutes	Only the 3 in use, then none once they're idle
How the model reaches tools	Default: codemode scripts. Per server: direct, or loaded by tool_search	Default: one mcp proxy tool. Per server: direct, or loaded by tool_search. Scripts: Pi's codemode (add "+codemode" to defaultTools) or the adapter's mcpScript, both opt-in
Token cost	By default, every call is a codemode script	Compared with the built-in's default, single lookups cost 10–33% less. For bulk work, turn on scriptMode; without it, bulk tasks cost up to 7× more (measured)
Tool search	tool_search, ranked by words	mcp({ search }) ranked by words or regex. With a System One key, semantic search ranks tools by meaning (setup)
OAuth tokens	JSON file in ~/.pi/agent	OS keychain
MCP prompts, elicitation, sampling, Tasks	No	Yes; Tasks need "protocolVersion": "auto"
MCP UI apps	Left out	Native window or browser
Add a server	pi mcp add in a shell, then /reload	Give the agent the URL: mcp({ action: "install", url }) connects it and checks its tools in the current session; for an OAuth server it opens sign-in first and checks the tools once you approve
Configs from Cursor, Claude Code, Codex, VS Code	Convert by hand	Imported
Guided setup in a session	No; /mcp manages servers that are already configured	/mcp-adapter setup overlay: imports configs found on your machine, adds presets (Figma desktop and RepoPrompt when installed, GitHub, Notion, Context7, DeepWiki, Parallel Search, Tavily Search, Chrome DevTools), and previews each file change before writing
Ask before risky tools	Through a permission extension, which sees every MCP call	Built in (approveTools); permission extensions see proxy calls as the proxy tool
Roots (session directory sent to servers)	Yes	No
Shell commands	pi mcp add, remove, list	pi-mcp-adapter init, doctor
Transports	stdio, streamable HTTP	stdio, streamable HTTP, legacy SSE, rmcp-mux socket

Over a session, measured with 100 small local servers:

100 servers installed, 3 used	Pi's built-in MCP	pi-mcp-adapter
Servers running at session start	100	0
While you use 3	100	3
After the idle timeout (10 min)	100	0

Stopping a server doesn't take its tools away: the model can still search them, and a stopped server starts again on its next call (0.1–0.3 s for a small local server). For a server that must keep state between calls, set "lifecycle": "lazy-keep-alive". The first session briefly starts new servers, 10 at a time, to read their tool lists. Measurements and details.

The full comparison has every row with sources, as of Pi 0.99.2.

When you install or update the adapter, it turns Pi's built-in MCP off in Pi's settings for you (the same switch as pi config → Built-in), so the two don't both run. If you remove the adapter, turn the built-in back on there (details).

Install

pi install npm:pi-mcp-adapter

Restart Pi after installation.

DeepSeek Harness (third-party bridge): Run the unmodified adapter in DSH via pi2dsh; see the verified dsh-TUI and Web MCP guide.

What happens on first run

The adapter reads standard MCP files automatically. No extra setup needed if you already have them.

You already have...	What happens
.mcp.json or ~/.config/mcp/mcp.json	Pi uses it immediately. Use .mcp.json for project/team sharing and ~/.config/mcp/mcp.json for all projects.
Servers added with pi mcp add (~/.pi/agent/mcp.json, .pi/mcp.json)	On Pi 0.99 and later, the adapter uses them and replaces Pi's built-in MCP extension, which Pi reports at startup; see Pi's built-in MCP.
Host-specific configs (Cursor, Claude Code, Codex, etc.) but no standard MCP files	Run /mcp-adapter setup to adopt those host configs into Pi. The setup flow shows exactly what it found, lets you pick which ones to import, and previews the exact file changes before writing.
Nothing configured yet	Run /mcp-adapter setup, choose project .mcp.json or global ~/.config/mcp/mcp.json, then scaffold a minimal config, add a curated known server, quick-add RepoPrompt, or inspect what the adapter discovered on your machine.

If you prefer the terminal, you can also run pi-mcp-adapter init after install to scan for host-specific configs and add missing compatibility imports to the adapter config (~/.pi/agent/mcp-adapter.json by default, or $PI_CODING_AGENT_DIR/mcp-adapter.json when set).

Quick Start

Add a server to .mcp.json in your project:

{
  "mcpServers": {
    "chrome-devtools": {
      "command": "npx",
      "args": ["-y", "chrome-devtools-mcp@1.6.0"]
    }
  }
}

Servers are lazy by default — they won't connect until you actually call one of their tools. The adapter caches tool metadata so search and describe work without live connections.

mcp({ search: "screenshot" })

chrome_devtools_take_screenshot
  Take a screenshot of the page or element.

  Parameters:
    format (enum: "png", "jpeg", "webp") [default: "png"]
    fullPage (boolean) - Full page instead of viewport

mcp({ tool: "chrome_devtools_take_screenshot", args: { format: "png" } })

Two calls instead of 26 tools cluttering the context.

Common tasks

Want	Do	Details
Add a server without editing JSON	/mcp-adapter setup, or mcp({ action: "install", url: "..." })	Configuration, Install from one URL
Use servers from Cursor, Claude Code, or Codex	/mcp-adapter setup or pi-mcp-adapter init	Import existing configs
Sign in to an OAuth server	/mcp-auth <server>	Authentication
Put a few tools directly in the model's tool list	"directTools": ["tool_a"] on the server	Direct tools
Ask before a risky tool runs	"approveTools": "destructive"	Tool approval
Keep a server running	"lifecycle": "keep-alive"	Lifecycle modes
Hide noisy tools	includeTools / excludeTools on the server	Search-activated direct tools
Chain many MCP calls in one step	settings.scriptMode: true, then mcpScript	MCP scripting
Use Figma	/mcp-adapter setup, add Figma (desktop)	Setup panel

Commands

Command	What it does
/mcp-adapter	Interactive panel and first-run onboarding surface
/mcp	Same as /mcp-adapter
/mcp-adapter setup	Guided setup for imports, a minimal .mcp.json, curated known servers, RepoPrompt quick-add, and config-path inspection
/mcp-adapter jev setup	Restrict which servers may share semantic-search data, save the project policy, and reload Pi
/mcp-adapter edit [project|global]	Open .mcp.json (default) or ~/.config/mcp/mcp.json in an editor; Ctrl+G opens $EDITOR; saves a valid JSONC object and reloads
/mcp-adapter tools	List all tools
/mcp-adapter prompts	List all MCP prompts registered as slash commands
/mcp-adapter reconnect	Reconnect all servers
/mcp-adapter reconnect <server>	Connect or reconnect a single server
/mcp-adapter disable <server>	Disable a server in the project-local .pi/mcp-adapter.json (requires /reload to apply)
/mcp-adapter enable <server>	Enable through the project-local override layer (requires /reload to apply)
/mcp-adapter logout <server>	Clear stored OAuth credentials for a server and disconnect it
/mcp-auth	Open an OAuth server picker in interactive UI sessions
/mcp-auth <server>	OAuth setup for a specific server

If settings.autoAuth is true, mcp({ connect: ... }), mcp({ tool: ... }), and direct tool calls automatically run OAuth when needed and retry once.

In interactive sessions, you can also authenticate from /mcp-adapter with ctrl+a or Enter on a server that needs auth. /mcp-auth without a server only opens a picker in the interactive UI. For gateway authorization and manual callback completion, see Remote/headless authentication.

On Pi 0.99 and later, servers you already signed in to with Pi's built-in MCP can reuse that sign-in: the adapter asks once per server, and /mcp-adapter offers ctrl+p to import them. See Import a sign-in from Pi's built-in MCP.

How It Works

• One mcp tool in context (~200 tokens) instead of hundreds
• Servers are lazy by default — they connect on first tool call, not at startup
• Tool metadata is cached to disk so search/list/describe work without live connections
• Idle servers disconnect after 10 minutes (configurable), reconnect automatically on next use
• npx-based servers resolve to direct binary paths, skipping the ~143 MB npm parent process
• MCP server validates arguments, not the adapter
• Remote keep-alive servers force-refresh their tool catalog during health checks, before user input, and before adapter-triggered turns, with bounded reconnect backoff
• Specific tools can be promoted from the proxy to first-class Pi tools via directTools config, so the LLM sees them directly instead of having to search

Limitations

• Each Pi session runs its own server processes; rmcp-mux can share one across sessions
• Compact MCP result rendering summarizes text, but inline images are still controlled by Pi's image display settings and may render below the compact text summary.
• Pi still owns one separator row before self-rendered tool output, so compact mode reduces adapter rendering height but cannot promise true zero-gap rows.
• MCP sampling support is text-only; context inclusion, tools, stop sequences, audio, and image content are rejected with explicit errors.

Documentation

The full reference lives in docs/:

Doc	What's in it
Configuration	The setup panel, config files and precedence, imports from other hosts, project server trust, lifecycle modes, and every settings key.
Server options	Every server field, custom HTTPS trust, macOS local-network access, protocol negotiation, MCP Tasks, stdio environment, rmcp-mux, and URL install.
Authentication	OAuth setup, remote and headless sign-in, token storage, headers, bearer tokens, and secret commands.
pi-mcp-adapter vs Pi's built-in MCP	Every difference, with sources, as of Pi 0.99.2.
Using MCP tools	The mcp tool, search and search keywords, direct tools, tool approval, and the output guard.
MCP scripting	Jev semantic search, the mcpScript tool, and composable tool search.
Prompts, elicitation, and MCP UI	MCP prompts as slash commands, servers asking for input, and interactive MCP UI windows.
Extension API, plugins, and SDK	Agent Plugins, Claude plugin bundles, Pi package manifests, runtime registration and tool calls, createMcpAdapter, host-managed embedding, and status events.