Loki Auto Server

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.

Available on the Chrome Web Store.

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🛠 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.

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🚀 Getting Started

1. Install the Browser Extension

• Chrome: Install directly from the Chrome Web Store.
• Firefox: Build from source and load manually (see Build from Source below).

2. Launch the Local MCP Server

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

You can download the pre-compiled loki-mcp-server binary for your platform from GitHub Releases and run it directly, or run it from source:

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

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Build from Source (Development / Firefox)

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 Manually

• 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.

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🔌 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.

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📝 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.

[!NOTE] The [timeout_ms] parameter in DOM APIs (e.g., click, type_text, type_as_human) specifies the maximum wait time for the target element to appear in the DOM before throwing a TimeoutError (defaults to 5000 ms). For type_as_human, this is the element detection limit and does not restrict the typing execution time itself (which runs asynchronously and is only limited by the global 45-second MCP oneshot task timeout).

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']");
}

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🛡 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.