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Windmill
Windmill is an open-source, self-hosted alternative to Retool that turns scripts into workflows, webhooks, and internal UIs with a fast Rust runtime.
Overview
Retool confines internal tools to a proprietary visual canvas with steep per-seat pricing, forcing developers to rewrite production scripts into browser queries. Windmill executes those scripts directly as backend jobs in Python, TypeScript, Go, or Bash, generating typed administrative forms and dashboards on private infrastructure. Powered by a Rust engine and PostgreSQL queues, it makes code the primary integration contract.
Why Windmill instead of Retool
Retool excels at quick drag-and-drop dashboards for operational teams, but its integration model centers on browser-mediated API requests and cloud proxies. For long-running batch jobs, asynchronous message handling, or access to isolated private networks, engineers often need external serverless functions or worker queues. Windmill unifies UI generation and backend orchestration into a single runtime. Integrations exist as typed, reusable resources stored in an encrypted vault, enabling scripts to consume events from Apache Kafka, AWS SQS, NATS, and incoming webhooks without extra infrastructure.
The trade-off lies between visual convenience and developer control. Building in Retool suits non-technical staff assembling dashboards from pre-built widgets, while Windmill requires developers to define typed parameters in standard code. Rebuilding rich UI layouts in Windmill requires upfront effort, but migrating backend logic from defunct platforms like Airplane or hosted tools like Pipedream is straightforward because scripts remain plain Git-synced files. Self-hosting Windmill also removes per-seat licensing barriers as internal usage expands.
What it does well
- Parameter-driven form generation converts TypeScript, Python, Go, Bash, and SQL function signatures into functional administrative interfaces.
- The Rust worker daemon polls PostgreSQL with sub-second dispatch latency, running tasks in isolated Linux namespaces via nsjail.
- OpenFlow DAG orchestration handles complex control flows, including parallel branches, dynamic loops, and human approval steps.
- Native Git synchronization pairs with a CLI and VS Code extension, allowing teams to manage scripts, resources, and flows in version control.
- Multi-runtime execution uses Bun for TypeScript and uv for Python, avoiding slow container builds for routine script updates.
- Inbound event triggers process webhooks, cron schedules, WebSockets, Kafka messages, and cloud queues directly.