LetCode

letcode is a terminal Agent written in Rust.

中文 | English

letcode is a terminal coding Agent built for developer productivity. Powered by Ratatui, it offers an interactive terminal user interface (TUI), a line-based REPL CLI, automated single-shot batch processing, and a built-in standard Agent Client Protocol (ACP) server.

Key Features

• Multi-Expert Collaboration: Six built-in subagents (explorer, fixer, oracle, designer, librarian, general) coordinated by a concurrent pool with path-based locking. The default expert mode keeps delegation with the parent; opt-in swarm mode adds recursive delegation and same-tree session messaging with shared tree limits. See Subagents.
• Terminal-Native Rich Rendering: Streams Markdown, renders LaTeX math formulas, and draws Mermaid vector diagrams (flowcharts, sequence diagrams, state diagrams) natively in the terminal grid.
• Native Multi-Protocol Support: Full native support for OpenAI Responses, Chat Completions, and Anthropic Messages protocols, including full-duplex WebSocket streaming for Responses.
• Layered Security & Permission Model: Four operational modes (safe, default, auto, yolo) with session-scoped grant tables and parameter fingerprinting.
• Intelligent Compaction & Long-Term Memory: Three-tier incremental history compaction via the internal historian expert, paired with a workspace-scoped SQLite store for long-term project memory.
• Extensible Ecosystem: Supports local stdio and remote HTTP Model Context Protocol (MCP) tool servers, alongside a native ACP server for seamless integration with modern editors like Zed.

Quick Start

1. Installation

Method A: Pre-built binaries (Recommended)

Download the pre-compiled archive for your platform from GitHub Releases. Releases currently include Linux x86-64/ARM64, macOS Intel/Apple Silicon, and Windows x86-64/ARM64. Extract the matching archive and place the letcode binary into your PATH.

Method B: Build from source

Ensure the Rust toolchain (1.85+ recommended) is installed, then run in the repository root:

cargo install --path .

2. Configuration

letcode loads its configuration from ~/.config/letcode/letcode.toml. Create this file with minimal settings:

#:schema https://raw.githubusercontent.com/letr007/letcode/main/letcode.schema.json

active_provider = "openai"

[providers.openai]
protocol = "responses"
default_model = "gpt-5.5"

[providers.openai.auth]
type = "bearer"
credential_env = "OPENAI_API_KEY"

[providers.openai.endpoints]
base_url = "https://api.openai.com/v1"

[providers.openai.models."gpt-5.5"]
display = "GPT-5.5"

Export your API key in your shell:

export OPENAI_API_KEY="your-api-key"

For advanced settings (multi-provider routing, subagent modes, timeouts, retries, MCP services, and environment disguises), see the Configuration Reference Manual.

3. Run

Launch the default terminal interface in any project directory:

letcode

The TUI supports English (en) and Simplified Chinese (zh-CN). Switch languages with /language zh-CN or /language en.

Common Commands

Use Case	Command Example	Description
Interactive TUI	letcode or letcode --tui	Launch the full-featured terminal interface (default)
Line REPL	letcode --cli or letcode repl	Launch the lightweight line-based CLI
Batch Processing	letcode -p "review git diff" --json	Single-shot prompt execution with streaming JSON output
Resume Session	letcode resume <session-id>	Restore conversation context and open the TUI
ACP Server	letcode acp	Start the stdio protocol server for Zed and other editors
Validate Config	letcode config validate	Validate letcode.toml syntax and model parameters
Check & Update	letcode update check letcode update	Check GitHub releases and perform an in-place atomic update

For detailed command-line options, see the CLI & Batch Processing Guide.

Technical Documentation

Comprehensive architectural and component documentation is available in the Technical Documentation Index. For contributor and maintenance test workflows, see the Testing Guide (in Chinese).

External Dependencies

Building from source requires the Rust toolchain. Some built-in tools also invoke external programs when available on PATH:

Program	Used by	Requirement
git	git__status, git__diff, git__log, and TUI branch indicator	Recommended; only Git tools and branch indicators are affected when missing
rg	search__rg fast text search	Recommended; search tools are unavailable when missing
ast-grep	code__ast_search and code__ast_replace_preview AST analysis	Optional; only AST tools are unavailable when missing

shell__exec and local MCP servers depend on the underlying system commands invoked; web__fetch and remote MCP servers require network access.

License

Dual-licensed under MIT and Apache-2.0. You may use, modify, or distribute this project under either license:

• MIT License: see LICENSE-MIT
• Apache License 2.0: see LICENSE-APACHE