# Letta Code (Research Preview)

A self-improving, stateful coding agent that can learn from experience and improve with use.

https://github.com/user-attachments/assets/5561a3ff-afd9-42a9-8601-55d245946394

---

## What is Letta Code?

Letta Code is a command-line harness around the stateful Letta [Agents API](https://docs.letta.com/api-reference/overview). You can use Letta Code to create and connect with any Letta agent (even non-coding agents!) - Letta Code simply gives your agents the ability to interact with your local dev environment, directly in your terminal.

Letta Code is model agnostic, and supports Sonnet 4.5, GPT-5, Gemini 2.5, GLM-4.6, and more.

> [!IMPORTANT]
> Letta Code is a **research preview** in active development, and may have bugs or unexpected issues. To learn more about the roadmap and chat with the dev team, visit our [Discord](https://discord.gg/letta). Contributions welcome, join the fun.

## Quickstart

> Get a Letta API key at: [https://app.letta.com](https://app.letta.com/)

Install the package via [npm](https://docs.npmjs.com/downloading-and-installing-node-js-and-npm):
```bash
npm install -g @letta-ai/letta-code
```

Set your Letta API key via environment variable:
```bash
export LETTA_API_KEY=...
```

Then run `letta` to start Letta Code (see various command-line options below):
```
letta
```

Any of the agents you create in Letta Code will be viewable (and fully interactable!) inside the [Agent Development Environment](https://app.letta.com).

## Persistence

All agents in Letta are **stateful**: they maintain context forever and can self-edit their own [memory blocks](https://www.letta.com/blog/memory-blocks). 

### Project-Level Agent Persistence

**Letta Code automatically remembers the last agent used in each directory.**
When you run `letta` in a project, it resumes where you left off with the same agent.

**How it works:**
- First time running `letta` in a directory → creates new agent (with shared memory blocks across all Letta Code agents)
- Subsequent runs → automatically resumes that agent
- Agent ID stored in `.letta/settings.local.json` (gitignored, personal to you)

```bash
letta                    # Auto-resumes project agent (or creates new if first time)
letta --new              # Force create new agent
letta --agent <id>       # Use specific agent ID
```

### Memory Configuration

Letta Code uses a hierarchical memory system:

**Global** (`~/.letta/settings.json`)
- API keys and credentials
- `persona` block - defines agent behavior 
- `human` block - stores user coding preferences

**Project** (`./.letta/settings.local.json`)  
- Last agent ID for this directory (auto-resumes)
- Gitignored - personal to you, not shared with your team

**Project Shared** (`./.letta/settings.json`)  
- `project` block - stores project-specific context
- Can be committed - shared with team

Memory blocks are highly configurable — see our [docs](https://docs.letta.com/guides/agents/memory-blocks) for advanced configuration options.
Join our [Discord](https://discord.gg/letta) to share feedback on persistence patterns for coding agents.

## Usage

### Interactive Mode
```bash
letta                    # Auto-resume project agent (or create new if first time)
letta --new              # Force create new agent
letta --agent <id>       # Use specific agent ID
letta --continue         # Resume global last agent (deprecated, use project-based)
```

### Headless Mode
```bash
letta -p "Run bun lint and correct errors"              # Auto-resumes project agent
letta -p "Pick up where you left off"                   # Same - auto-resumes by default
letta -p "Start fresh" --new                            # Force new agent
letta -p "Run all the test" --allowedTools "Bash"       # Control tool permissions
letta -p "Just read the code" --disallowedTools "Bash"  # Control tool permissions

# Pipe input from stdin
echo "Explain this code" | letta -p
cat file.txt | letta -p
gh pr diff 123 | letta -p --yolo

# Output formats
letta -p "Analyze this codebase" --output-format json         # Structured JSON at end
letta -p "Analyze this codebase" --output-format stream-json  # JSONL stream (one event per line)
```

You can also use the `--tools` flag to control the underlying *attachment* of tools (not just the permissions).
Compared to disallowing the tool, this will additionally remove the tool schema from the agent's context window.
```bash
letta -p "Run all tests" --tools "Bash,Read"         # Only load specific tools
letta -p "Just analyze the code" --tools ""          # No tools (analysis only)
```

Use `--output-format json` to get structured output with metadata:
```bash
# regular text output
$ letta -p "hi there"
Hi! How can I help you today?

# structured output (single JSON object at end)
$ letta -p "hi there" --output-format json
{
  "type": "result",
  "subtype": "success",
  "is_error": false,
  "duration_ms": 5454,
  "duration_api_ms": 2098,
  "num_turns": 1,
  "result": "Hi! How can I help you today?",
  "agent_id": "agent-8ab431ca-63e0-4ca1-ba83-b64d66d95a0f",
  "usage": {
    "prompt_tokens": 294,
    "completion_tokens": 97,
    "total_tokens": 391
  }
}
```

Use `--output-format stream-json` to get streaming outputs, in addition to a final JSON response.
This is useful if you need to have data flowing to prevent automatic timeouts:
```bash
# streaming JSON output (JSONL - one event per line, token-level streaming)
# Note: Messages are streamed at the token level - each chunk has the same otid and incrementing seqId.
$ letta -p "hi there" --output-format stream-json
{"type":"init","agent_id":"agent-...","model":"claude-sonnet-4-5-20250929","tools":[...]}
{"type":"message","messageType":"reasoning_message","reasoning":"The user is asking","otid":"...","seqId":1}
{"type":"message","messageType":"reasoning_message","reasoning":" me to say hello","otid":"...","seqId":2}
{"type":"message","messageType":"reasoning_message","reasoning":". This is a simple","otid":"...","seqId":3}
{"type":"message","messageType":"reasoning_message","reasoning":" greeting.","otid":"...","seqId":4}
{"type":"message","messageType":"assistant_message","content":"Hi! How can I help you today?","otid":"...","seqId":5}
{"type":"message","messageType":"stop_reason","stopReason":"end_turn"}
{"type":"message","messageType":"usage_statistics","promptTokens":294,"completionTokens":97,"totalTokens":391}
{"type":"result","subtype":"success","result":"Hi! How can I help you today?","agent_id":"agent-...","usage":{...}}
```

### Permissions

**Tool selection** (controls which tools are loaded):
```bash
--tools "Bash,Read,Write"                        # Only load these tools
--tools ""                                       # No tools (conversation only)
```

**Permission overrides** (controls tool access, applies to loaded tools):
```bash
--allowedTools "Bash,Read,Write"                 # Allow specific tools
--allowedTools "Bash(npm run test:*)"            # Allow specific commands
--disallowedTools "Bash(curl:*)"                 # Block specific patterns
--permission-mode acceptEdits                    # Auto-allow Write/Edit tools
--permission-mode plan                           # Read-only mode
--permission-mode bypassPermissions              # Allow all tools (use carefully!)
--yolo                                           # Alias for --permission-mode bypassPermissions
```

Permission modes:
- `default` - Standard behavior, prompts for approval
- `acceptEdits` - Auto-allows Write/Edit/NotebookEdit
- `plan` - Read-only, allows analysis but blocks modifications
- `bypassPermissions` - Auto-allows all tools (for trusted environments)

Permissions are also configured in `.letta/settings.json`:
```json
{
  "permissions": {
    "allow": ["Bash(npm run lint)", "Read(src/**)"],
    "deny": ["Bash(rm -rf:*)", "Read(.env)"]
  }
}
```

## Self-hosting

To use Letta Code with a self-hosted server, set `LETTA_BASE_URL` to your server IP, e.g. `export LETTA_BASE_URL="http://localhost:8283"`.
See our [self-hosting guide](https://docs.letta.com/guides/selfhosting) for more information.

## Installing from source

First, install Bun if you don't have it yet: [https://bun.com/docs/installation](https://bun.com/docs/installation)

### Run directly from source (dev workflow)
```bash
# install deps
bun install

# run the CLI from TypeScript sources (pick up changes immediately)
bun run dev
bun run dev -- -p "Hello world"  # example with args
```

### Build + link the standalone binary
```bash
# build bin/letta (includes prompts + schemas)
bun run build

# expose the binary globally (adjust to your preference)
bun link

# now you can run the compiled CLI
letta
```
> Whenever you change source files, rerun `bun run build` before using the linked `letta` binary so it picks up your edits.

---

Made with 💜 in San Francisco