letcode

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letcode is a terminal Agent written in Rust. It provides an opencode-style TUI based on Ratatui by default, while keeping a REPL CLI mode available.

Build and test

cargo build
cargo test
cargo fmt --check

Run the default TUI:

cargo run

Run the line-based CLI:

cargo run -- --cli

CLI mode can also be selected with cli or repl. TUI can be selected explicitly with --tui or tui.

Configuration

letcode loads configuration from:

~/.config/letcode/letcode.toml

Minimal example:

active_provider = "openai"

[global]
max_iterations = 64
max_tool_calls = 128
sessions_dir = "sessions"
log_file = "logs/combined.log"

[permissions]
mode = "default"

[providers.openai]
api_key = "YOUR_API_KEY"
base_url = "https://api.openai.com/v1"
protocol = "responses" # responses/completions
default_model = "gpt-5.5"

[providers.openai.models."gpt-5.5"]
display_name = "GPT-5.5"
supports_tools = true
supports_reasoning = true
reasoning_effort = "medium"
reasoning_summary = "auto"
text_verbosity = "medium"

Provider API keys and base URLs can also come from environment variables. The variable names are generated from the provider name:

export OPENAI_API_KEY="..."
export OPENAI_BASE_URL="https://api.openai.com/v1"

If the provider is named compat, the corresponding variables are COMPAT_API_KEY and COMPAT_BASE_URL.

Relative sessions_dir and log_file paths are resolved relative to the config file directory.

Project layout

src/main.rs          entry point, config loading, TUI/CLI selection
src/config.rs        TOML config parsing and validation
src/agent.rs         model loop, tool execution, turn lifecycle
src/tool.rs          built-in tool registry and tool result model
src/permission.rs    permission modes, scopes, and request classification
src/transcript.rs    JSONL transcript persistence and restore helpers
src/subagent.rs      subagent-related code
src/mcp.rs           MCP tool discovery
src/tui/             Ratatui/Crossterm UI, runtime, state, events, rendering

License

This project is dual-licensed under the MIT License OR the Apache License 2.0. You may choose either license when using, modifying, or redistributing this project.

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