Inspector Jake

Direct your agent to make updates with point and click.

What is Inspector Jake?

Inspector Jake is an MCP (Model Context Protocol) server that connects AI assistants like Claude to Chrome DevTools. Agents can inspect page structure via ARIA trees, capture screenshots, read console logs, monitor network requests, and interact with elements through clicks, typing, and navigation.

Session Management

When the MCP server starts, it automatically picks an available session name and port. Use get_session_info to find out which session you're on, and set_session_name to switch.

Getting the Session Name

The agent should call get_session_info at the start of a conversation to tell you which session to connect to in the Chrome extension:

// Response from get_session_info
{
  "sessionName": "annie",
  "port": 52992,
  "browserConnected": true,
  "connectedTab": { "id": 123, "title": "My App", "url": "https://myapp.com" }
}

Open the Inspector Jake DevTools tab and connect to the session name shown above.

Changing the Session Name

Use set_session_name to switch to a different session at runtime. Predefined names (jake, annie, kevin, elsa) are auto-discovered by the Chrome extension. Custom names work too — the response includes the port for manual connection.

// Request
{ "name": "jake" }

// Response
{
  "message": "Switched session from \"annie\" to \"jake\"",
  "sessionName": "jake",
  "port": 52340,
  "previousName": "annie",
  "previousPort": 52992
}

After switching, re-scan sessions in the Chrome extension and connect to the new name. The previous browser connection is dropped.

DevTools Panel

The Inspector Jake DevTools panel is your workspace for capturing elements, annotating them for the AI agent, and reviewing computed styles and accessibility trees.

Jake's Notes

Pin elements or drag to capture regions, then add notes for the AI agent. Notes appear as context when the agent calls see_jakes_notes. Use them for requests like "make this button bigger", "fix the alignment here", or "this color is wrong".

Why ARIA Trees Instead of Raw HTML

Inspector Jake uses ARIA accessibility trees instead of raw HTML for page inspection. Raw HTML is too verbose and noisy for LLM context windows. ARIA trees are a compact, semantic representation — roles, names, and states capture what the user sees and can interact with. Each element gets a ref (e.g., s1e42) that maps directly to interaction tools like click_element and type_into_element.

Computed Styles & Send Styles

The CSS panel shows computed styles for selected elements. The Send Styles setting controls how much CSS context the agent receives when it reads selections:

• None — Skip computed styles entirely (saves tokens)
• Lean — Layout + visual essentials (display, flex, padding, colors, fonts)
• Non-Default — Only properties changed from browser defaults
• All — Every computed property (most verbose)

Configuration

• Computed Styles — Choose how much CSS context to send (None / Lean / Non-Default / All)
• Screenshot Capture — Max Dimension — Screenshots exceeding this limit (200–2000px, default 800) are downscaled proportionally
• Auto-clear Selections — Clears captures automatically after the agent reads them via see_jakes_notes

Architecture

┌─────────────────┐                    ┌─────────────────────┐
│   AI Agent      │───MCP Protocol────▶│   MCP Server        │
│ (Claude, etc)   │                    │   inspector-jake    │
└─────────────────┘                    └──────────┬──────────┘
                                                  │ WebSocket
                                                  ▼
                                       ┌─────────────────────┐
                                       │  Chrome Extension   │
                                       │  (connected tab)    │
                                       └──────────┬──────────┘
                                                  │
                                                  ▼
                                       ┌─────────────────────┐
                                       │  DevTools Panel     │
                                       │  (element tracking) │
                                       └─────────────────────┘

Quick Start

1. Install the MCP Server

npx inspector-jake-mcp

2. Configure Your MCP Client

For Codex CLI, use Codex's MCP manager with the npm package directly:

# 1) Add Inspector Jake MCP server to Codex
codex mcp add inspector-jake -- npx -y inspector-jake-mcp@1.0.10

# 2) Verify it was added
codex mcp list
codex mcp get inspector-jake

Important: do not configure Codex with command: inspector-jake-mcp directly unless that binary is globally installed. Use npx as shown above.

If you see No such file or directory (os error 2), re-add with the full npx path:

which npx
codex mcp remove inspector-jake
# Replace /opt/homebrew/bin/npx with the path printed by `which npx`
codex mcp add inspector-jake -- /opt/homebrew/bin/npx -y inspector-jake-mcp@1.0.10

For Claude Code (global, available in all projects):

claude mcp add --scope user --transport stdio inspector-jake -- npx -y inspector-jake-mcp

For Claude Code (project-scoped):

claude mcp add --transport stdio inspector-jake -- npx -y inspector-jake-mcp

For Claude Desktop, add to your config (~/.config/claude/claude_desktop_config.json on macOS/Linux):

{
  "mcpServers": {
    "inspector-jake": {
      "command": "npx",
      "args": ["-y", "inspector-jake-mcp"]
    }
  }
}

For other MCP clients (generic stdio):

{
  "inspector-jake": {
    "command": "npx",
    "args": ["-y", "inspector-jake-mcp"],
    "transport": "stdio"
  }
}

Updating

If you configured your client with npx -y inspector-jake-mcp (no pinned version), you'll automatically get the latest version next time the server starts. No action needed.

If you pinned a version (e.g. inspector-jake-mcp@1.0.10), update the version number in your config or re-run the mcp add command with the new version.

If you installed globally:

npm update -g inspector-jake-mcp

3. Load the Chrome Extension

1. Open Chrome and go to chrome://extensions/
2. Enable "Developer mode" (toggle in top right)
3. Click "Load unpacked"
4. Select the packages/chrome-extension/dist folder

For Chrome Web Store upload, create a zip from inside dist:

cd packages/chrome-extension/dist
zip -r ../../../inspector-jake-chrome-store.zip .

Important: the zip must contain manifest.json at the root (not inside a top-level dist/ folder).

4. Connect

1. Navigate to any webpage
2. Open DevTools (F12)
3. Click the "Jake" tab
4. Click "Connect" to your MCP session

MCP Tools (17)

Inspection

Tool	Description
get_page_info	Page URL, title, viewport, and full ARIA accessibility tree with element refs
get_session_info	MCP session name, port, and browser connection status
set_session_name	Switch session to a different name and port at runtime
see_jakes_notes	All user-pinned selections from the DevTools panel
view_image_in_jakes_notes	View a stored selection image by its ID
capture_screenshot	Screenshot by element ref, CSS selector, or full page
get_console_logs	Console output and uncaught errors (log, warn, error, info, debug, trace, assert, exceptions)
get_network_requests	Captured fetch/XHR network requests with URL, method, status, headers, and timing
run_javascript	Execute JavaScript in the page context

Interaction

Tool	Description
click_element	Click an element by ref or CSS selector
type_into_element	Type text into an input by ref or CSS selector
select_dropdown_option	Select an option from a <select> dropdown
wait_for_element	Wait until a CSS selector matches an element on the page

Navigation

Tool	Description
navigate_to_url	Navigate the browser to a URL
go_back	Navigate back in browser history
go_forward	Navigate forward in browser history
reload_page	Reload the current page

Tool Examples

get_page_info

Returns page metadata and an ARIA tree with interactive element refs (e.g., s1e42) that can be used with click_element, type_into_element, and other interaction tools.

Response:

Page: Example Page
URL: https://example.com
Viewport: 1920x1080

- navigation [s1e1|nav]
  - link "Home" [s1e2|a.nav-link]
  - link "About" [s1e3|a.nav-link:nth-of-type(2)]
- main [s1e4|main]
  - heading "Welcome" [level=1] [s1e5|h1]
  - textbox "Search" [s1e6|input#search]
  - button "Submit" [s1e7|button.btn]

capture_screenshot

Request:

{
  "selector": "#submit-btn"
}

Returns a base64-encoded PNG image of the matched element.

click_element

Request (by ref from get_page_info):

{
  "ref": "s1e7"
}

Request (by CSS selector):

{
  "selector": "#submit-btn",
  "clickCount": 2
}

get_console_logs

Request:

{
  "types": ["error", "warn"],
  "clear": true
}

Response:

{
  "logs": [
    {"type": "error", "message": "Uncaught TypeError: x is not a function", "timestamp": 1700000000000},
    {"type": "warn", "message": "Deprecated API usage", "timestamp": 1700000001000}
  ]
}

get_network_requests

Request:

{
  "urlPattern": "/api/",
  "method": "POST",
  "statusMin": 400,
  "clear": true
}

Response:

{
  "requests": [
    {
      "url": "https://example.com/api/users",
      "method": "POST",
      "status": 422,
      "statusText": "Unprocessable Entity",
      "type": "fetch",
      "requestHeaders": { "content-type": "application/json" },
      "responseHeaders": { "content-type": "application/json" },
      "duration": 145,
      "timestamp": 1700000000000
    }
  ]
}

All parameters are optional. Omit them to get all captured requests. Captures fetch() and XMLHttpRequest traffic — does not include request/response bodies.

run_javascript

Request:

{
  "code": "document.title"
}

Response:

{
  "result": "My App - Dashboard"
}

Session Discovery

The extension discovers MCP servers using predefined session names (jake, annie, kevin, elsa), each mapped to a deterministic port via hash. When the MCP server starts, it picks the first available name and listens on its port. The extension scans all four ports to find active servers.

You can also switch to a custom session name at runtime using set_session_name. Custom names get a deterministic port but won't be auto-discovered by the extension — the agent will tell you the port number for manual connection.

Development

Prerequisites

• Node.js 18+
• npm 9+
• Chrome browser

Setup

git clone https://github.com/inspectorjake/inspector-jake.git
cd inspector-jake
npm install
npm run build
npm test

Project Structure

inspector-jake/
├── packages/
│   ├── mcp-server/          # MCP server (npm package)
│   │   ├── src/
│   │   │   ├── index.ts           # CLI entry
│   │   │   ├── server.ts          # MCP server + tools
│   │   │   ├── ws-server.ts       # WebSocket for extension
│   │   │   └── response-builder.ts # Response formatting utilities
│   │   └── package.json
│   │
│   ├── chrome-extension/    # Chrome extension (Manifest V3)
│   │   ├── src/
│   │   │   ├── background/  # Service worker
│   │   │   ├── content/     # Content script
│   │   │   ├── devtools/    # DevTools panel
│   │   │   └── popup/       # Extension popup (Vue)
│   │   ├── manifest.json
│   │   └── package.json
│   │
│   └── shared/              # Shared types and utilities
│       └── package.json
│
└── package.json             # Workspace root

Watch Mode

# In separate terminals:
cd packages/shared && npm run dev
cd packages/mcp-server && npm run dev
cd packages/chrome-extension && npm run dev

Contributing

See CONTRIBUTING.md for development guidelines.

Security

See SECURITY.md for security policy.

License

MIT - see LICENSE