How do I install Pen?

Copy the stdio config for Cursor, Claude Desktop, Claude Code, or VS Code on this page. It uses the publisher's install, not a PlugMCP proxy.

Does Pen need an API key?

No required environment variable is listed on this record.

When was Pen last checked?

Last checked 2026-10-28. MCP server that connects AI assistants to Chrome DevTools.

Pen MCP server

PEN

MCP server that connects AI assistants to Chrome DevTools. Ask your AI to profile a page, find a memory leak, or measure coverage — PEN runs the browser profiling and returns structured results.

Single Go binary. No Node.js. No browser launch. Attach to your dev browser and go.

Install

Quick install (recommended):

# macOS / Linux
curl -fsSL https://raw.githubusercontent.com/edbnme/pen/main/install.sh | sh

# Windows (PowerShell)
irm https://raw.githubusercontent.com/edbnme/pen/main/install.ps1 | iex

Then run the interactive setup wizard:

pen init

Package managers:

# macOS / Linux
brew install edbnme/tap/pen

# Windows
scoop bucket add pen https://github.com/edbnme/scoop-pen
scoop install pen

Other options:

# Download binary from GitHub Releases (all platforms)
# → https://github.com/edbnme/pen/releases/latest

# Or install with Go 1.23+
go install github.com/edbnme/pen/cmd/pen@latest

Verify it works:

pen --version

More install methods (from source, manual binary setup): docs/INSTALL.md

Quick Start

The fastest way to get going is the interactive setup wizard:

pen init

This auto-detects your environment, lets you pick your IDE and browser, generates the MCP config, and optionally launches your browser with debugging — all in one command.

Manual setup

If you prefer to configure things by hand:

1. Launch a debug browser — PEN can do this automatically:

pen --auto-launch

This detects an installed browser, launches it with a separate debug profile (your existing browser stays untouched), and connects via CDP. No need to close your browser or manage anything manually.

Use --user-data-dir so it doesn't conflict with your existing browser:

macOS:

open -a "Google Chrome" --args --remote-debugging-port=9222 --user-data-dir=/tmp/pen-debug-profile --no-first-run

Windows (PowerShell):

& "C:\Program Files\Google\Chrome\Application\chrome.exe" --remote-debugging-port=9222 --user-data-dir="$env:TEMP\pen-debug-profile" --no-first-run

Linux:

google-chrome --remote-debugging-port=9222 --user-data-dir=/tmp/pen-debug-profile --no-first-run &

Verify the debug port is open — visit http://localhost:9222/json in a new tab. You should see a JSON array.

Why --user-data-dir? Chrome's debug port flag is silently ignored when Chrome is already running. --user-data-dir forces a separate instance that works alongside your existing browser.

2. Add PEN to your IDE

VS Code — create .vscode/mcp.json in your project:

{
  "servers": {
    "pen": {
      "command": "pen",
      "args": ["--auto-launch", "--project-root", "${workspaceFolder}"]
    }
  }
}

Cursor — .cursor/mcp.json in your project (or ~/.cursor/mcp.json for global):

{
  "mcpServers": {
    "pen": {
      "command": "pen",
      "args": ["--auto-launch", "--project-root", "${workspaceFolder}"]
    }
  }
}

Claude Desktop — config path:

{
  "mcpServers": {
    "pen": {
      "command": "pen",
      "args": ["--auto-launch", "--project-root", "/absolute/path/to/project"]
    }
  }
}

3. Use it

Open a page in the debug browser, then ask your AI:

"Check the performance metrics of this page"

PEN connects to the browser, runs the profiling, and returns structured results.

Flags

Flag	Default	Purpose
`--cdp-url`	`http://localhost:9222`	CDP endpoint
`--transport`	`stdio`	`stdio`, `http`, or `sse`
`--addr`	`localhost:6100`	Bind address for HTTP/SSE
`--allow-eval`	`false`	Enable `pen_evaluate` (runs JS in browser)
`--project-root`	`.`	Sandbox for source file paths
`--stateless`	`false`	Stateless HTTP mode (no session tracking)
`--log-level`	`info`	`debug` / `info` / `warn` / `error`
`--version`	—	Print version and exit

Tools

30 tools across 9 categories:

Category	Tools
Performance	`pen_performance_metrics` · `pen_web_vitals` · `pen_accessibility_check`
Memory	`pen_heap_snapshot` · `pen_heap_diff` · `pen_heap_track` · `pen_heap_sampling`
CPU	`pen_cpu_profile` · `pen_capture_trace` · `pen_trace_insights`
Network	`pen_network_enable` · `pen_network_waterfall` · `pen_network_request` · `pen_network_blocking`
Coverage	`pen_js_coverage` · `pen_css_coverage`
Source	`pen_list_sources` · `pen_source_content` · `pen_search_source`
Console	`pen_console_enable` · `pen_console_messages`
Lighthouse	`pen_lighthouse`
Utility	`pen_status` · `pen_list_pages` · `pen_select_page` · `pen_navigate` · `pen_collect_garbage` · `pen_screenshot` · `pen_emulate` · `pen_evaluate`

Full schemas: docs/spec/08-tool-catalog.md

Architecture

AI Assistant ◄── stdio/JSON-RPC ──► PEN (Go) ── CDP/WebSocket ──► Chrome (localhost:9222)

cmd/pen/          Entry point, flags, signals
internal/
  cdp/            CDP connection, target management
  server/         MCP server, locking, progress
  tools/          Tool handlers (one file per category)
  format/         Output formatting
  security/       Validation, rate limiting, temp files

New in this release: console.go (real-time console capture via Runtime CDP domain), lighthouse.go (Lighthouse CLI integration), pen_navigate in utility.go (browser navigation control), and pen_trace_insights in cpu.go (offline trace analysis engine).

Security

Localhost only — rejects remote CDP URLs
No browser launch — attaches to existing browser
Eval gated — pen_evaluate needs --allow-eval
Expression blocklist — blocks fetch, document.cookie, eval, etc. even with eval on
Path sandboxing — source tools can't escape --project-root
Temp isolation — snapshots/traces go to $TMPDIR/pen/ with 0600 perms
Rate limiting — cooldowns on heap snapshots, traces, and other heavy ops
Size caps — 2 GB max heap snapshot, 500 MB max trace capture
Graceful shutdown — 5-second grace period for in-progress operations on SIGINT/SIGTERM

Docs

Doc	What's in it
Getting Started	Install, browser setup, IDE config
Running PEN	Usage, Docker, server deploys, troubleshooting
Tool Catalog	Every tool's params and output
Security Model	Threat model, defenses
System Architecture	Design and tech stack

PEN

MCP server that connects AI assistants to Chrome DevTools. Ask your AI to profile a page, find a memory leak, or measure coverage — PEN runs the browser profiling and returns structured results.

Single Go binary. No Node.js. No browser launch. Attach to your dev browser and go.

Install

Quick install (recommended):

# macOS / Linux
curl -fsSL https://raw.githubusercontent.com/edbnme/pen/main/install.sh | sh

# Windows (PowerShell)
irm https://raw.githubusercontent.com/edbnme/pen/main/install.ps1 | iex

Then run the interactive setup wizard:

pen init

Package managers:

# macOS / Linux
brew install edbnme/tap/pen

# Windows
scoop bucket add pen https://github.com/edbnme/scoop-pen
scoop install pen

Other options:

# Download binary from GitHub Releases (all platforms)
# → https://github.com/edbnme/pen/releases/latest

# Or install with Go 1.23+
go install github.com/edbnme/pen/cmd/pen@latest

Verify it works:

pen --version

More install methods (from source, manual binary setup): docs/INSTALL.md

Quick Start

The fastest way to get going is the interactive setup wizard:

pen init

This auto-detects your environment, lets you pick your IDE and browser, generates the MCP config, and optionally launches your browser with debugging — all in one command.

Manual setup

If you prefer to configure things by hand:

1. Launch a debug browser — PEN can do this automatically:

pen --auto-launch

Use --user-data-dir so it doesn't conflict with your existing browser:

macOS:

open -a "Google Chrome" --args --remote-debugging-port=9222 --user-data-dir=/tmp/pen-debug-profile --no-first-run

Windows (PowerShell):

& "C:\Program Files\Google\Chrome\Application\chrome.exe" --remote-debugging-port=9222 --user-data-dir="$env:TEMP\pen-debug-profile" --no-first-run

Linux:

google-chrome --remote-debugging-port=9222 --user-data-dir=/tmp/pen-debug-profile --no-first-run &

Verify the debug port is open — visit http://localhost:9222/json in a new tab. You should see a JSON array.

Why --user-data-dir? Chrome's debug port flag is silently ignored when Chrome is already running. --user-data-dir forces a separate instance that works alongside your existing browser.

2. Add PEN to your IDE

VS Code — create .vscode/mcp.json in your project:

{
  "servers": {
    "pen": {
      "command": "pen",
      "args": ["--auto-launch", "--project-root", "${workspaceFolder}"]
    }
  }
}

Cursor — .cursor/mcp.json in your project (or ~/.cursor/mcp.json for global):

{
  "mcpServers": {
    "pen": {
      "command": "pen",
      "args": ["--auto-launch", "--project-root", "${workspaceFolder}"]
    }
  }
}

Claude Desktop — config path:

{
  "mcpServers": {
    "pen": {
      "command": "pen",
      "args": ["--auto-launch", "--project-root", "/absolute/path/to/project"]
    }
  }
}

3. Use it

Open a page in the debug browser, then ask your AI:

"Check the performance metrics of this page"

PEN connects to the browser, runs the profiling, and returns structured results.

Flags

Flag	Default	Purpose
`--cdp-url`	`http://localhost:9222`	CDP endpoint
`--transport`	`stdio`	`stdio`, `http`, or `sse`
`--addr`	`localhost:6100`	Bind address for HTTP/SSE
`--allow-eval`	`false`	Enable `pen_evaluate` (runs JS in browser)
`--project-root`	`.`	Sandbox for source file paths
`--stateless`	`false`	Stateless HTTP mode (no session tracking)
`--log-level`	`info`	`debug` / `info` / `warn` / `error`
`--version`	—	Print version and exit

Tools

30 tools across 9 categories:

Category	Tools
Performance	`pen_performance_metrics` · `pen_web_vitals` · `pen_accessibility_check`
Memory	`pen_heap_snapshot` · `pen_heap_diff` · `pen_heap_track` · `pen_heap_sampling`
CPU	`pen_cpu_profile` · `pen_capture_trace` · `pen_trace_insights`
Network	`pen_network_enable` · `pen_network_waterfall` · `pen_network_request` · `pen_network_blocking`
Coverage	`pen_js_coverage` · `pen_css_coverage`
Source	`pen_list_sources` · `pen_source_content` · `pen_search_source`
Console	`pen_console_enable` · `pen_console_messages`
Lighthouse	`pen_lighthouse`
Utility	`pen_status` · `pen_list_pages` · `pen_select_page` · `pen_navigate` · `pen_collect_garbage` · `pen_screenshot` · `pen_emulate` · `pen_evaluate`

Full schemas: docs/spec/08-tool-catalog.md

Architecture

AI Assistant ◄── stdio/JSON-RPC ──► PEN (Go) ── CDP/WebSocket ──► Chrome (localhost:9222)

cmd/pen/          Entry point, flags, signals
internal/
  cdp/            CDP connection, target management
  server/         MCP server, locking, progress
  tools/          Tool handlers (one file per category)
  format/         Output formatting
  security/       Validation, rate limiting, temp files

Security

Localhost only — rejects remote CDP URLs
No browser launch — attaches to existing browser
Eval gated — pen_evaluate needs --allow-eval
Expression blocklist — blocks fetch, document.cookie, eval, etc. even with eval on
Path sandboxing — source tools can't escape --project-root
Temp isolation — snapshots/traces go to $TMPDIR/pen/ with 0600 perms
Rate limiting — cooldowns on heap snapshots, traces, and other heavy ops
Size caps — 2 GB max heap snapshot, 500 MB max trace capture
Graceful shutdown — 5-second grace period for in-progress operations on SIGINT/SIGTERM

Docs

Doc	What's in it
Getting Started	Install, browser setup, IDE config
Running PEN	Usage, Docker, server deploys, troubleshooting
Tool Catalog	Every tool's params and output
Security Model	Threat model, defenses
System Architecture	Design and tech stack

Add this server

Host a copy with our keys and logs.

Server facts

Tools

Questions

How do I install Pen?

Does Pen need an API key?

What transport does Pen use?

When was Pen last checked?

Documentation

PEN

Install

Quick Start

Manual setup

2. Add PEN to your IDE

3. Use it

Flags

Tools

Architecture

Security

Docs

Add this server

Host a copy with our keys and logs.

Server facts

Tools

Questions

How do I install Pen?

Does Pen need an API key?

What transport does Pen use?

When was Pen last checked?

Documentation

PEN

Install

Quick Start

Manual setup

2. Add PEN to your IDE

3. Use it

Flags

Tools

Architecture

Security

Docs