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Web Development · head to head

FastAPI vs Keycloak

FastAPI logo

FastAPI

Web Development

A modern, fast, high-performance web framework for building APIs with Python

From
Free
Free plan
Yes
Full reviewWebsite
Keycloak logo

Keycloak

Developer Tools

Open-source identity and access management server.

From
Free
Free plan
Yes
Full reviewWebsite

The short version

  • Each has a real cost: FastAPI no built-in ORM, requires separate database libraries; Keycloak requires self-hosted deployment and operational expertise to install, configure and maintain
  • Prices and features above were last checked on 29 August 2026.

Where they differ

Only the attributes on which FastAPI and Keycloak actually diverge.

Attributes where FastAPI and Keycloak differ
AttributeFastAPIKeycloak
PlatformsWebSelf-hosted, Docker, Kubernetes, Linux, Windows, API
CategoryWeb DevelopmentDeveloper Tools

Identical on both: starting price (Free), pricing model (open-source), free tier (Yes), user rating (Not yet rated).

What people use each for

The jobs each tool is most often brought in to do.

FastAPI

  • Building production-ready REST APIs with automatic validationnot Keycloak
  • Serving machine learning model predictions as REST servicesnot Keycloak
  • Building crisis management and orchestration platformsnot Keycloak
  • Enabling real-time APIs with WebSocket connectionsnot Keycloak
  • Rapid API development reducing boilerplate code significantlynot Keycloak

Keycloak

  • Organisations requiring self-hosted identity infrastructure for compliance or data residencynot FastAPI
  • Companies with existing LDAP/Active Directory systems needing federated authenticationnot FastAPI
  • Open-source projects and communities requiring free IAM without licensing costsnot FastAPI
  • Enterprises building custom identity workflows requiring fine-grained authorisationnot FastAPI
  • Teams with sufficient operational expertise to manage infrastructurenot FastAPI

Where each one falls short

Documented limitations, not opinions. Every one is a constraint you would hit in normal use.

FastAPI

  • No built-in ORM, requires separate database libraries
  • Python-only, cannot build with other languages
  • Async/await learning curve for developers new to async programming
  • Production deployment requires separate ASGI server configuration

Keycloak

  • Requires self-hosted deployment and operational expertise to install, configure and maintain
  • No managed cloud option provided by Red Hat; organisations must operate infrastructure themselves or use third-party distributions
  • Clustering and high-availability configurations require additional operational knowledge
  • Community support only; commercial support requires third-party vendors or distributions

Pricing, plan by plan

FastAPI

Free

No published plan breakdown. See the FastAPI review.

Keycloak

Free
  • Open-sourceFree
    • Full platform functionality
    • Self-hosted deployment
    • Community support

Which should you pick?

Choose FastAPI if

  • You want to start without paying.
FastAPI review

Choose Keycloak if

  • You want to start without paying.
  • You work on Self-hosted, Docker, Kubernetes, Linux, Windows, API.
Keycloak review

Questions people ask

Is FastAPI or Keycloak better?
Neither clearly leads. FastAPI starts at Free and Keycloak at Free, and user ratings are close enough to be indistinguishable. Choose on capability and platform support.
Which is cheaper, FastAPI or Keycloak?
FastAPI starts at Free and Keycloak at Free.
Does FastAPI or Keycloak run on more platforms?
FastAPI runs on Web. Keycloak runs on Self-hosted, Docker, Kubernetes, Linux, Windows, API.
Can I use FastAPI for free?
Both have a free tier, so you can try either at no cost before committing.
What is FastAPI best used for?
FastAPI is most often used for building production-ready rest apis with automatic validation, serving machine learning model predictions as rest services, building crisis management and orchestration platforms, enabling real-time apis with websocket connections. Of those, building production-ready rest apis with automatic validation and serving machine learning model predictions as rest services are not what Keycloak is typically brought in for.

Answered from the vendors’ own pages

FastAPI: Is FastAPI free to use?

Yes. FastAPI is free and open-source under the MIT License. It costs nothing to download, use, or deploy in production. An optional paid service, FastAPI Cloud, offers one-command deployment for additional convenience, but the core framework is free.

Source
Keycloak: What protocols does Keycloak support?

Keycloak supports OpenID Connect, OAuth 2.0 and SAML 2.0 protocols for authentication and authorisation.

Source
FastAPI: Can I use FastAPI for commercial applications?

Yes. FastAPI's MIT License permits unrestricted commercial use, modification, and distribution. You can build and sell products powered by FastAPI without licensing fees or restrictions.

Source
Keycloak: Can Keycloak integrate with existing user directories?

Yes. Keycloak supports user federation with LDAP and Active Directory systems, allowing organisations to leverage existing user directories.

Source
FastAPI: Does FastAPI include a database or ORM?

No. FastAPI does not include a built-in database or ORM. You must add separate libraries like SQLAlchemy for database access. This gives flexibility to choose the database solution best suited to your project.

Source
Keycloak: Is Keycloak free?

Yes. Keycloak is fully open-source and free to deploy and use. No licensing fees are required.

Source
FastAPI: What Python versions does FastAPI support?

FastAPI supports Python 3.7 and later. Older Python versions are not compatible, so you must run at least Python 3.7 to use FastAPI.

Source
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