# Writing APIs
You can create node.js/typescript APIs using Stormkit.
## Serverless functions on self-hosted instances
On Stormkit Cloud, functions run on managed function infrastructure (AWS Lambda). A
self-hosted instance has none by default, so it forks a short-lived `node` process per
invocation instead — fine for parity and local development, but not for production
traffic.
For a self-hosted backend, use a
[**Start command**](/docs/deployments/application-runtime) and run a long-lived server.
See [when to use it](/docs/deployments/application-runtime) for the trade-offs.
## How it works
> **Note: On Stormkit Cloud, function timeouts are set at 15 seconds. If you require a different timeout, please inform us, and we can adjust it to suit your workflow. Work that legitimately runs longer — headless-browser rendering, video processing, large report generation — does not belong in a function. Self-hosted instances do not apply this limit, but a function still forks a fresh `node` process per request; run that kind of work behind a [Start command](/docs/deployments/application-runtime) server instead.**
During build time, Stormkit checks if there is a `.stormkit/api` folder. When the folder is found,
it uploads the folder to a lambda function. The entry file of the function then takes the `Request` and calls the relevant file based on file system routing. If nothing is found, it returns 404.
## Write and deploy your API
Create an `/api` folder in the top level of your repository and an `/index.ts` file in it.
Each file is treated as a separate endpoint and it needs to export a default function
with the signature shown below.
```ts
// api/index.ts
import http from 'http'
export default (req: http.IncomingMessage, res: http.ServerResponse) => {
res.write('Function endpoint: /api')
res.end()
}
```
```ts
// api/user/subscribe.ts
import http from 'http'
export default (req: http.IncomingMessage, res: http.ServerResponse) => {
res.write('Function endpoint: /api/user/subscribe')
res.end()
}
```
The table below shows how the API routing works.
```ts
+ /api
- index.ts // /api
+ /users
- index.ts // /api/users
- subscribe.ts // /api/users/subscribe
- create.ts // /api/users/create
+ /[id]
- remove.ts // /api/users/:id/remove (where :id is a placeholder for dynamic values)
```
For more details on how the filesystem routing works, check the
source code of the matchPath function.
