Ein

Ein is a Rust-based AI agent framework. A gRPC server drives an LLM agent loop (powered by Claude via OpenRouter) and executes tools implemented as pluggable WASM modules. A terminal UI client connects to the server and provides an interactive chat interface.

┌─────────────────────────┐          ┌──────────────────────────────┐
│        ein-tui          │   gRPC   │          ein-server          │
│                         │◄────────►│                              │
│  Interactive chat UI    │          │  LLM agent loop              │
│  Connection retry       │          │  WASM tool executor          │
│  Slash command hints    │          │  OpenRouter client           │
│  Animated thinking UI   │          │  Per-session sandboxing      │
└─────────────────────────┘          └──────────────────────────────┘

Getting Started

Prerequisites

• Sign up for OpenRouter and create an API key
• Install Rust

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

Setup

Add the WASM compile target

rustup target add wasm32-wasip2

Build the WASM plugins (Bash, Read, Write, Edit tools)

./scripts/build_install_plugins.sh

In debug builds, plugins are loaded automatically from ./target/wasm32-wasip2/debug/ — no installation needed.

Configure credentials

Before running, add your OpenRouter API key to ~/.ein/config.json (created automatically on first TUI launch):

{
  "plugin_configs": {
    "ein_openrouter": {
      "config": {
        "api_key": "sk-or-...",
        "base_url": "https://openrouter.ai/api/v1"
      }
    }
  }
}

Running

Start the server in one terminal:

cargo run -p ein-server

Start the TUI client in another:

cargo run -p ein-tui

On first launch a floating dialog asks whether to grant the agent access to your current working directory for that session. The TUI connects to localhost:50051 by default. To connect to a different address:

cargo run -p ein-tui -- http://my-server:50051

Configuration

The TUI stores its configuration at ~/.ein/config.json. The file is created with defaults on first run.

{
  "allowed_paths": [],
  "allowed_hosts": [],
  "plugin_configs": {
    "ein_openrouter": {
      "config": {
        "api_key": "sk-or-...",
        "base_url": "https://openrouter.ai/api/v1",
        "model": "anthropic/claude-haiku-4.5",
        "max_tokens": "2500"
      }
    }
  }
}

Global fields

Field	Description
allowed_paths	Filesystem paths all WASM plugins may read/write (preopened for every session)
allowed_hosts	Hostnames all WASM plugins may connect to (empty = deny all; "*" = allow all)

In addition, at startup the TUI asks whether to add the current working directory to allowed_paths for that session only — this is never written back to config.json.

Per-plugin configuration (plugin_configs)

plugin_configs is a map keyed by plugin filename stem (e.g. "ein_openrouter", "ein_bash"). Each entry can contain:

Field	Description
allowed_paths	Additional filesystem paths for this plugin only, merged with the global list
allowed_hosts	Additional hostnames for this plugin only, merged with the global list
config	Arbitrary key-value pairs forwarded to the plugin at instantiation

Known config keys for ein_openrouter:

Key	Description
api_key	Your OpenRouter API key
base_url	Model API endpoint; restricts outbound connections to that host (empty = deny all; "*" = allow all)
model	OpenRouter model ID
max_tokens	Maximum tokens per LLM response

Changes to config.json are picked up automatically while the TUI is running — plugin config updates take effect without restarting.

Usage

Type a message and press Enter to send it to the agent. Type / to see available slash commands.

Key	Action
Enter	Send message / run slash command
↑ / ↓	Scroll conversation history
Ctrl-C	Force quit
/exit + Enter	Exit the TUI

While the agent is working, an animated indicator appears in the chat panel. Tool invocations are shown inline as the agent uses them:

 ▸ Bash  ls -la
 ▸ Read  src/main.rs
 ▸ Write  src/main.rs
 ▸ Edit  src/main.rs

Edit calls display a syntax-highlighted diff showing the removed and added lines.

The status bar at the bottom shows the active model and cumulative token usage for the session.

Connection behaviour

The TUI starts immediately regardless of whether the server is running. While disconnected, a red ● icon and animated spinner appear in the conversation pane. The TUI reconnects automatically every 3 seconds. If the server goes away mid-session, an error message is shown and the TUI resumes connecting in the background.

Tools

Tools are WASM components loaded at startup. Three are included out of the box:

Tool	Description
Bash	Execute shell commands
Read	Read a file from the filesystem
Write	Write content to a file
Edit	Replace a specific string in a file with new content

Adding a tool

1. Create a new package under packages/ implementing the ToolPlugin trait from packages/ein_tool/
2. Add it to scripts/build_install_plugins.sh
3. Rebuild — the server picks it up automatically on next start

Architecture

crates/
  ein-proto/    Protocol Buffer definitions (gRPC service + message types)
  ein-server/   gRPC server — agent loop, WASM plugin host
  ein-tui/      Terminal UI client
packages/
  ein_tool/     WASM plugin interface (ToolPlugin trait, ToolDef, syscalls)
  ein_bash/     Bash tool plugin
  ein_read/     Read tool plugin
  ein_write/    Write tool plugin
  ein_edit/     Edit tool plugin

The protocol (crates/ein-proto/proto/ein.proto) defines a bidirectional streaming RPC. Each session opens with a SessionConfig message (global sandbox constraints + per-plugin config map), followed by UserInput prompt messages. The server streams back AgentEvent messages as the agent thinks, calls tools, and produces output. A config_update message variant allows the TUI to push plugin config changes to a live session without reconnecting.