Langflow

1.9.1 verified Fri May 01 auth: no python

Langflow is a low-code Python package for building AI agents and RAG applications through a visual flowchart interface. Version 1.9.1 is the latest; the project follows a monthly release cadence. It supports Python >=3.10 and includes a built-in web application for drag-and-drop workflow design.

pip install langflow

Common errors

error ModuleNotFoundError: No module named 'langflow.server' ↓

cause Import path changed in v1.0; old import no longer exists.

fix

Change from langflow.server import app to from langflow import start.

error RuntimeError: Could not find browser revision. Please run `playwright install`. ↓

cause Playwright browsers are not installed alongside the Python package.

fix

Run playwright install chromium in your terminal.

error sqlalchemy.exc.OperationalError: (sqlite3.OperationalError) database is locked ↓

cause Multiple processes (e.g., multiple Uvicorn workers) accessing the default SQLite database concurrently.

fix

Set LANGFLOW_DATABASE_URL to a PostgreSQL connection string, e.g., postgresql://user:pass@localhost:5432/langflow.

Warnings

breaking In v1.0, the import path for the main entry point changed from `langflow.server` to `langflow`. Old code `from langflow.server import app` will fail. ↓

fix Use `from langflow import start` or `from langflow import Langflow`.

deprecated The `langflow run` CLI command is deprecated in favor of `langflow serve` or the Python API. ↓

fix Use `langflow serve` or call `start()` from Python.

gotcha Langflow stores flow data in a SQLite database by default; it is not thread-safe for multiple processes. Running multiple workers may cause database corruption. ↓

fix Set the `LANGFLOW_DATABASE_URL` environment variable to a PostgreSQL database for production.

gotcha When using Playwright for headless browser automation, ensure the Playwright browsers are installed (e.g., `playwright install chromium`). Missing browsers cause `RuntimeError: Could not find browser revision`. ↓

fix Run `playwright install chromium` after installing Langflow.

Install

pip install langflow[all]

Imports

Langflow
wrong
```
import langflow
```
correct
```
from langflow import Langflow
```
Direct import of module does not expose the main class; use from langflow import Langflow
start
wrong
```
from langflow.server import start
```
correct
```
from langflow import start
```
The start function moved in v1.0+ to the top-level package

Quickstart

Start the Langflow web application programmatically. The server will be accessible at http://127.0.0.1:7860.

from langflow import start

# Start Langflow server on default port 7860
start(
    host="127.0.0.1",
    port=7860,
    open_browser=False,
    components_path="./components",
    log_level="INFO"
)