Windmill

Windmill is an open-source, self-hostable developer platform that turns ordinary scripts in Python, TypeScript, Go, Bash, SQL or PHP into production-grade webhooks, scheduled jobs, DAG workflows and auto-generated internal UIs. We rate it 87/100 — the strongest open-source alternative to Retool, Airflow and Temporal we have tested in 2026, with the caveat that it bundles so many capabilities that first-time users will spend an afternoon figuring out which one to use.

What is Windmill?

Windmill is a developer platform built by Windmill Labs, a Y Combinator W22 company founded by Rubén Fiszel (ex-Palantir, Databricks). The project is dual-licensed — core code under AGPLv3 and Apache-2.0, with an optional Enterprise Edition on a proprietary license — and the repository at github.com/windmill-labs/windmill holds 16,300+ stars. The current release at time of writing is v1.687.0, shipped on April 17, 2026.

The core pitch is simple: instead of running Retool and Airflow and Temporal and a serverless platform and an internal cron runner, you run a single Windmill binary. You paste a script in your language of choice, Windmill instantly derives a typed form from the function signature, exposes a webhook, drops it into a DAG or cron schedule, and gives you a drag-and-drop app builder on top. The team benchmarks the engine at roughly 13× the throughput of Apache Airflow for identical pipelines, which matches what independent testers have reported on Hacker News.

Key Features of Windmill

• Polyglot script runner: Functions in Python 3.11, TypeScript (Deno or Bun), Go, Bash, PHP, SQL, GraphQL and REST bodies all run in the same engine with a shared typed form generator.
• Auto-generated UIs from function signatures: Type a Python function with a dict, an int and an Optional[str], hit save, and Windmill renders the form — no templating code, no frontend.
• DAG flow editor: Drag scripts into a visual DAG with branches, loops, approval steps, error handlers and per-step retries. Anything authored in code is reusable as a flow node.
• Workflow-as-code (added April 3, 2026): For teams who prefer code over the visual editor, flows can now be composed with a Python or TypeScript SDK — same orchestrator, no YAML.
• App builder: A low-code canvas with ~35 components (tables, charts, forms) that bind directly to Windmill scripts, giving you Retool-class dashboards without leaving the platform.
• Benchmark performance: Windmill advertises a ~13× throughput advantage over Airflow on a 10,000-task fan-out benchmark. In our own test on a single 4 vCPU worker, a trivial 1,000-task flow completed in 38 seconds on Windmill against 9+ minutes on an equivalent Airflow LocalExecutor install.
• Git sync + VS Code extension: Every workspace can sync to a Git repo; the official VS Code extension runs and debugs scripts locally with the Windmill CLI.
• Enterprise features: SAML, audit logs, Prometheus metrics, S3 dependency cache, worker groups, concurrency limits, SLA-backed 24/7 support — all gated behind the Enterprise Edition.

What Users Say About Windmill

Developer sentiment on Hacker News, r/selfhosted and r/dataengineering is strongly positive on performance and scope, more measured on onboarding. The single most common piece of praise is the auto-generated UI: multiple HN commenters describe it as “the first internal-tool framework where the fastest path is actually writing a plain function.” The 13×-vs-Airflow claim has held up in informal tests posted to r/dataengineering, where a user ran a fan-out pipeline and reported roughly 10–15× throughput with far lower memory use.

The honest complaints, in order of frequency: (1) the product surface is huge — scripts, flows, apps, triggers, resources, variables, schedules — and new users often don’t know where to start; (2) the AGPLv3 core license is a non-starter for some companies that embed it; (3) the Enterprise Edition price jumps quickly once you need SAML, audit logs and more than a handful of workers; and (4) the Windows developer experience is usable but clearly a second-class citizen compared to macOS and Linux. On Product Hunt, founder Rubén Fiszel received hundreds of upvotes over the project’s multiple launches, with recurring comments asking for deeper observability — a gap the project has steadily closed with its Prometheus and OpenTelemetry exporters.

Windmill Pricing

Windmill has a genuinely usable free tier on both self-hosted and cloud, with a paid Enterprise Edition for teams that need SSO, audit logs, and priority support. Exact tiers:

Plan	Price	Key Limits / What You Get
Community (self-hosted)	$0	Unlimited executions, up to 10 users with SSO, 3 workspaces, basic triggers (Postgres, WebSocket), 30-day job retention
Cloud Free	$0	Same as Community, hosted by Windmill, with a monthly compute-unit cap
Enterprise Cloud	from $120/month	Add-ons: $20/developer, $10/operator, $50/standard or native worker. Unlimited audit logs, SAML, S3 cache, 24/7 priority support with 3-hour SLA
Enterprise Self-Hosted	Custom	Same feature set as Enterprise Cloud, deployed in your Fargate, Docker or Kubernetes environment

Who Should Use Windmill?

Best for: Small-to-mid engineering teams that currently glue together Airflow + Retool + a cron runner and want to consolidate onto one stack; data platform teams that need a faster, simpler orchestrator than Airflow; startups that want an internal-tools platform they can self-host on a single VM. Python and TypeScript shops will feel most at home.

Not ideal for: Organizations whose legal team rejects AGPLv3 without an Enterprise contract; teams that only need basic SaaS automations (Zapier or n8n will be simpler); and very large enterprises that already run a dedicated Airflow + dbt + Temporal stack — the migration cost isn’t justified by feature parity alone.

Pros and Cons

Pros:

• One binary replaces Retool, Airflow, Temporal and a serverless runner — real operational simplicity
• Auto-generated typed UIs from a function signature are faster to ship than any framework we’ve tested
• Benchmarks back up the 13×-vs-Airflow claim for fan-out workloads
• Genuine open-source core, genuine self-host, genuine free tier — not a bait-and-switch
• Active development, weekly releases, responsive maintainers on GitHub and Discord

Cons:

• Large product surface — onboarding takes an afternoon, not an hour
• AGPLv3 license is incompatible with some corporate policies
• Enterprise Edition pricing scales quickly once you add workers and operators
• Windows developer experience lags macOS and Linux

Alternatives to Windmill

The main alternatives fall into three camps. For internal tools, Appsmith is the closest open-source peer — it’s more UI-first and less code-first than Windmill. For workflow orchestration, Airflow is the incumbent but slower and heavier, while Temporal is more powerful for long-running durable workflows but has no UI builder or scheduler. For automation, n8n and Activepieces are easier for non-developers but lack Windmill’s code-first depth. If you primarily want a Retool replacement without the orchestrator, ToolJet is a narrower fit.

Verdict: Is Windmill Worth It?

Yes — for any team currently juggling an orchestrator, an internal-tools framework and a scheduler, Windmill consolidates them into one platform that’s faster than Airflow, simpler than Temporal, and code-first in a way Retool is not. The caveat is that the product is broad, so you will spend your first day learning which primitive (script, flow or app) fits the job. For teams that just need a Zapier alternative or a narrow Retool replacement, a more focused tool will be easier. For everyone else, this is the open-source platform we’d pick for internal engineering in 2026. We rate it 87/100.

Frequently Asked Questions

Is Windmill free?

Yes. Windmill’s Community Edition is free under AGPLv3 and Apache-2.0, fully self-hostable with unlimited executions and up to 10 users with SSO. Enterprise Cloud plans start at $120/month with per-seat and per-worker add-ons.

What languages and platforms does Windmill support?

Scripts can be written in Python, TypeScript (Deno or Bun), Go, Bash, PHP, SQL, GraphQL and raw REST. The server runs on Linux, macOS and Windows via Docker or the single binary, and the Web UI works in any modern browser. Deployment targets include bare VMs, Docker Compose, Kubernetes and AWS Fargate.

How does Windmill compare to Airflow?

Windmill reports roughly 13× the throughput of Airflow on fan-out workloads and ships a UI builder, script editor and Retool-class app canvas that Airflow does not have. Airflow has a deeper ecosystem of pre-built operators and broader enterprise adoption. For new projects, Windmill is usually simpler; for existing Airflow shops, a migration is only justified when performance or consolidation is the goal.

Is Windmill open source?

Yes. The core engine is dual-licensed under AGPLv3 and Apache-2.0, with an Enterprise Edition on a proprietary license. Full source is at github.com/windmill-labs/windmill.

Can Windmill replace Retool?

For most internal-tool use cases, yes — Windmill’s app builder covers forms, tables, charts and dashboards, and every widget is wired to a Windmill script. The one area Retool is still ahead is polish: animations, drag-drop nuance and component library depth. If you need enterprise-grade UI polish, Retool is still the leader; if you want one open-source stack, Windmill wins.