loki-auto (Open-Source Edition)

loki-auto is an ultra-lightweight, zero-dependency "Serverless in Browser" web automation runtime designed for the AI Agent era. It executes episodic, transient LLM tool actions inside a secure Rhai VM (compiled to WebAssembly) sandbox container directly within the browser's foreground page context, completely bypassing heavy headless browser resource overhead.

🛠 Architecture

loki-auto uses a stateless, event-driven Oneshot CGI paradigm:

graph TD
    A[LLM Agent / Orchestrator] <-->|MCP Protocol over Stdio| B[Axum MCP Server Host]
    B <-->|WebSocket ws://127.0.0.1:10402| C[Browser Extension BG Script]
    C <-->|chrome.runtime Messages| D[Active Tab Content Script]
    D -->|Instantiates On-Demand| E[Rhai WASM VM Sandbox]
    E -->|Synchronous DOM interactions| F[Page DOM]

1. Layer 1: Host Environment – Rust Axum MCP server handling Model Context Protocol (MCP) tool bindings and bridging commands over local WebSockets.

2. Layer 2: Browser Background – Extension background script managing tab states and routing target instructions.

3. Layer 3: Browser Sandbox – The content script instantiates a lightweight WASM-compiled Rhai VM per prompt invocation, executes DOM operations, captures results/logs, and purges the VM from memory instantly.

Related MCP server: WebControl

🚀 Getting Started

1. Prerequisites

Ensure you have the following installed on your system:

• Bun (Workspace package manager)

• Rust & Cargo (with wasm32-unknown-unknown target installed: rustup target add wasm32-unknown-unknown)

• wasm-pack (for Rust-to-WASM compilation)

2. Compilation and Build

Build the WebAssembly sandbox first, and then compile the extension assets:

# 1. Compile Rust Sandbox to WebAssembly
cd packages/sandbox
wasm-pack build --target web

# 2. Return to root, install dependencies and compile the Chrome/Firefox extensions
cd ../..
bun install
bun run build

This will output two fully-compiled, self-contained extension directories under the root folder:

• Chrome (Manifest V3): ./dist/chrome

• Firefox (Manifest V2): ./dist/firefox

3. Load the Browser Extension

• Firefox: Open about:debugging#/runtime/this-firefox, click "Load Temporary Add-on...", and select the compiled package loki-auto.xpi at the root of the project (or select ./dist/firefox/manifest.json).

• Chrome: Open chrome://extensions/, enable Developer mode, click "Load unpacked", and select the ./dist/chrome folder.

4. Launch the Local MCP Server

Start the Axum host to begin listening for browser connections and LLM tool calls:

# Start the MCP host (default port: 10402)
cargo run --bin loki-mcp-server

🔌 MCP Tool Specifications

loki-auto exposes standard Model Context Protocol (MCP) tools:

• list_tabs - Lists all open browser tabs and their focused states.

• open_tab(url, active) - Opens a new tab with the specified URL.

• close_tab(tab_id) - Closes a target tab by ID.

• activate_tab(tab_id) - Focuses a browser tab to the foreground.

• execute_loki_oneshot(target_tab_id, target_url_pattern, rhai_script, payload) - Runs a Rhai automation script synchronously inside the sandboxed VM of the target tab.

📝 Rhai Sandbox DOM APIs

Scripts running inside the WASM sandbox have access to the following synchronous DOM hooks:

• sleep(ms) - Suspends execution for the specified milliseconds.

• log(message) - Prints a message/object to the execution console logs.

• dom_to_string() -> String - Returns a cleaned, token-optimized (AEO-optimized) HTML tree of the current page.

• element_exists(selector) -> bool - Immediate check if a element matches the CSS selector.

• wait_element(selector, [timeout_ms]) -> bool - Blocks until the element is present, or throws a timeout exception.

• click(selector, [timeout_ms]) -> bool - Wait and click on the selected element.

• type_text(selector, text, [timeout_ms]) -> bool - Wait and instantly set text into an input or textarea, triggering input events (recommended for long texts/articles).

• type_as_human(selector, text, [timeout_ms]) -> bool - Wait and type text character-by-character with randomized human typing delays and standard keydown/keyup events (recommended for search boxes and login inputs).

• get_text(selector, [timeout_ms]) -> String - Extract inner text content.

• get_value(selector, [timeout_ms]) -> String - Extract form input value.

• get_attribute(selector, attr, [timeout_ms]) -> String - Extract specific attribute value.

• scroll_to(selector, [timeout_ms]) -> bool - Scroll the viewport smoothly to the targeted element.

• get_loki_data(dom_selector, [timeout_ms]) -> String - Scopes target DOM and extracts child nodes bearing data-loki attributes in a clean, Markdown-friendly format.

Example Rhai Script

print("Interacting with search input...");
if wait_element("textarea[name='q']", 2000) {
  type_text("textarea[name='q']", "weather in Boston today");
  sleep(500);
  click("input[name='btnK']");
}

🛡 Security and Isolation

• Strict Sandbox: The Rhai runtime inside WebAssembly has no access to standard JS APIs, cookies, localStorage, or system files unless explicitly exposed through bridge bindings.

• No Network Access: The sandbox cannot perform fetch or AJAX requests. All actions occur inside the page context, and results are returned via the secure extension channel.