The FastAPI approach.
FastAPI serves typed request and response models for an API. The interface consuming that API is a separate concern.
Keep your FastAPI services. Add a Python-authored interface.
Build user interfaces around your existing FastAPI services in the same language, calling them from Reflex event handlers.
Build the application your team needs.
Give an existing API a real interface without a separate frontend project.
Bring it together with Reflex.
Call existing FastAPI endpoints from Python event handlers. Build user-facing forms, tables, charts, and navigation with UI components.
Keep the work you can build on.
Reuse existing endpoint contracts, authentication, and validation. Call them from Reflex event handlers rather than rewriting the service.
Compare the details.
Compare what you can build, how you can extend it, and where it can run. Explore the sources for each product.
What this comparison covers
Compares FastAPI with the Reflex framework and its optional AI development and hosting products. Sources describe each product’s development model; these are not performance benchmarks.
Scroll horizontally to compare →
| Decision | FastAPI | Reflex |
|---|---|---|
| API layer | Typed request and response models with automatic docs. | Call existing FastAPI endpoints from Python event handlers. |
| Interface | Not included. Pair with a separately built frontend for the application architecture. | Build user-facing forms, tables, charts, and navigation with UI components. |
| Validation and actions | Validates request data and supports reusable dependencies. | Handle UI actions in Python and call existing APIs, retaining server-side validation and authorization. |
Python teams building the whole application.
SellerX compared development with Reflex against its React and FastAPI stack. The World Bank uses Reflex alongside existing FastAPI services.
“With Reflex it is ten times faster than developing with React and FastApi.”
Know which part of Reflex you need.
Framework, AI development, hosting, and enterprise services have different responsibilities and entitlements.
Open-source framework
The Apache 2.0 Python framework is available independently of Build and managed hosting. Your app still depends on Reflex and its other packages.
Reflex Build
The AI development product generates and edits framework-based apps. Usage, private projects, repository access, and export entitlements belong to your plan.
Hosting and App Management
Managed deployment is an operating service. You can also self-host a framework app, providing its frontend, Python backend, configuration, and maintenance.
Enterprise
Enterprise packages and services have separate entitlements. Workspace SSO is distinct from app-user authentication. Authorization, auditing, and private deployment need configuration and an agreed operating plan.
Start with one workflow.
A focused pilot lets you validate the interface, business rules, and operating model before a wider rollout. The example below uses synthetic data.
Build a service request portal.
Document the endpoint
Use two staging requests and record the create, list, and status response contracts.
Create the interface
Build a form and request list in Reflex. Call the existing FastAPI endpoints from backend handlers.
Handle the lifecycle
Show request REQ-101 as queued, then completed. Make validation errors and network failures visible to users.
Verify the boundary
Confirm the persisted request matches the form, authentication reaches the service correctly, and retries do not duplicate work.
What a passing pilot looks like
A valid request is created once, appears in the list, and shows its saved status. Invalid inputs and unavailable services produce actionable errors.
Make the move one workflow at a time.
Prove the pattern on one feature before committing the rest of the roadmap.
An API does not define the complete user journey. Design application state, navigation, permissions, and recovery paths alongside the existing service contracts.
Plan application authentication, authorization, monitoring, and maintenance with your team. The framework, Reflex Build, managed hosting, and enterprise services have separate responsibilities and entitlements.
Questions before you choose.
The practical details, before you make a move.
Why build with Reflex instead of FastAPI?
Build user interfaces around your existing FastAPI services in the same language, calling them from Reflex event handlers.
Can Reflex call our existing FastAPI endpoints?
Yes. Call them from server-side Python handlers with your chosen HTTP client. Preserve the API’s authentication and validation rules and handle failures in the interface.
Can we choose where the Reflex app runs?
Yes. Use managed Reflex hosting or self-host the framework’s frontend and Python backend. Self-hosting includes responsibility for configuration, secrets, scaling, and operations.
How should we validate the first release?
A valid request is created once, appears in the list, and shows its saved status. Invalid inputs and unavailable services produce actionable errors.
Bring one workflow. Build a useful first version.
Install Reflex and start building your application in Python.