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Create or import your app

Backends


Frameworks

Create a FastAPI app or use an existing one:

FastAPI

Deploy a FastAPI app to Vercel with the Python runtime and Vercel Functions. Vercel looks for a FastAPI instance named app at supported entrypoints in your repository.

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Deploy a FastAPI app on Vercel

Get started with Vercel CLI

Initialize a new FastAPI project with the Vercel CLI init command:

vc initfastapi


This clones the FastAPI example repository in a directory called fastapi.

Exporting the FastAPI application

To run a FastAPI application on Vercel, define an app instance that initializes FastAPI at a supported entrypoint:

  • app.py, index.py, server.py, main.py, wsgi.py, or asgi.py
  • the same filenames inside src/ or app/

For example:

@app.get("/")

app =FastAPI()

from fastapi import FastAPI

[tool.vercel]

defread_root():

return{"Python":"on Vercel"}

[tool.vercel.scripts]

For example:

if__name__=="__main__":

build ="python build.py"

f.write("BUILD_COMMAND")

main()

defmain():

withopen("build.txt", "w")as f:

print("Running build command...")

The build property in [tool.vercel.scripts] defines the Build Command for FastAPI deployments. It runs after dependencies are installed and before your application is deployed.

Build Command in vercel.json or in the Project Settings dashboard, it takes precedence over a build script in pyproject.toml.

Local development

Use vercel dev to run your application locally.

python -mvenv.venv

source.venv/bin/activate

pip install-rrequirements.txt

vercel dev


Deploying the application

Deploy the project by connecting your Git repository or by using the Vercel CLI:

vc deploy



Serving frontend and static assets

Vercel supports two methods for serving frontend and static assets with FastAPI.

The public/ directory

Place files in a public/ directory at your project root. Vercel serves them from the CDN at the matching root URL paths. For example, public/logo.svg is served at /logo.svg. Default response headers apply unless you override them in vercel.json.

from fastapi import FastAPI


app =FastAPI()

asyncdeffavicon():

from fastapi.responses import RedirectResponse

returnRedirectResponse("/vercel.svg", status_code=307)

@app.get("/favicon.ico", include_in_schema=False)

# /vercel.svg is served automatically from public/vercel.svg.

Do not mount the

public/

directory with

app.mount()

. Vercel handles it at the platform level.

Built-in FastAPI frontend and static file support

When using app.frontend() or app.mount() with StaticFiles, files are promoted to the CDN at build time:

app.frontend


app =FastAPI()

defhello():

@app.get("/api/hello")

return{"message":"Hello"}

from fastapi import FastAPI

app.frontend("/", directory="dist")

Promoted source directories are kept in the function bundle by default so the app can read from them at runtime. To exclude them and serve files from the CDN only, set exclude = true:


exclude =true

Route precedence for app.mount()

[tool.vercel.fastapi.static]

Files are served from the CDN at the mount's URL prefix. Route declaration order determines which wins when a route and a CDN file share the same path:

See Configuration for all available settings.

  • A route declared before the mount takes priority over CDN files. Matching requests reach the function.
  • A route declared after the mount does not take priority. Matching requests are served from the CDN.

File served

from fastapi.staticfiles import StaticFiles

"auto"

@app.get("/static/protected.json")

app =FastAPI()
return{"access":"denied"}
Status

fallback value

app.mount("/static", StaticFiles(directory="static"))

defprotected():
When applied
All misses
Navigation requests only

"404.html"

# Declared before the mount, so this route wins over any CDN file at this path.

n/a
"index.html"
See notes below
index.html

An index.html fallback applies to navigation requests only: requests with an explicit text/html or application/xhtml+xml Accept header and an extension-less final URL segment (for example, /dashboard but not /dashboard/app.js). All other misses reach the function. A 404.html fallback applies to every miss regardless of the Accept header. If "auto" is set but neither file exists in the build directory, no fallback is applied.

Fallback routes apply to GET and HEAD requests only. All other methods always reach the function.

Middleware

CDN-served files bypass the function entirely, so middleware handlers and Depends() guards do not run for them.

Vercel detects these cases and keeps the affected static files and frontends in the function rather than promoting them to the CDN:

  • Top-level middleware: All static mounts and frontends stay in the function.
  • Sub-app middleware: Only that sub-app's mounts stay in the function. Mounts elsewhere are still promoted.
  • Frontend dependencies: Frontends with Depends() guards stay in the function.

Set cdn = true to promote files to the CDN even when middleware or dependency guards are present:

[tool.vercel.fastapi.static]

cdn =true


Configuration

All settings go under [tool.vercel.fastapi.static] in pyproject.toml.

Our Services

Setting

cdn

CDN promotion always enabled, even when middleware or dependency guards are present.

omitted (default)
Value
CDN promotion enabled. Disabled automatically when middleware or dependency guards are present.
true

cdn

exclude

false (default)
CDN promotion disabled. All requests reach the function.
cdn
Promoted source directories are kept in the function bundle.

Software Delivery

exclude

false
Description
Promoted source directories are excluded from the function bundle.
true

Startup and shutdown

You can use FastAPI lifespan events to manage startup and shutdown logic, such as initializing and closing database connections.


@asynccontextmanager

from fastapi import FastAPI

# Startup logic

print("Starting up...")

from contextlib import asynccontextmanager

yield

# Shutdown logic

awaitstartup_tasks()

awaitcleanup_tasks()

asyncdeflifespan(app: FastAPI):

app =FastAPI(lifespan=lifespan)

Vercel Functions

SIGTERM signal. Logs printed during the shutdown step will not appear in the Vercel dashboard.

When you deploy a FastAPI app to Vercel, it becomes a single Vercel Function. Vercel uses Fluid compute by default, so the function scales with traffic.

To configure that function, add an entry to the functions object in vercel.json keyed by your resolved entrypoint file. For example, to let an app defined in app/main.py run for up to 60 seconds, set maxDuration:


{

}

"functions": {

"app/main.py": {

"$schema":"https://openapi.vercel.sh/vercel.json",

For more options, see Configuring functions and the functions property.

}

}

"maxDuration":60

All Vercel Functions limitations apply to FastAPI applications, including:

Application size: The FastAPI application becomes a single bundle, which has a standard bundle size limit of 500MB. Large Functions support Python bundles up to 5GB on Fluid compute when enabled (public beta).

More resources

Last updated August 27, 2026

For more about deploying FastAPI on Vercel, see:

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