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Tuesday, November 12th 2019

Customizing Serverless Functions

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When extending your project with Serverless Functions, you might find yourself in a situation where adjusting the default behavior is necessary.

Today, we are adding a new functions configuration property to allow you to do just this.

Note: To take advantage of this feature, you need to use our Git Integration or Vercel CLI.

Custom Memory & Execution Duration

In most cases, zero configuration is required to create deployments with Vercel. Every Serverless Function (in all projects created after November 8th) receives the following attributes by default:

  • Memory: 1024 MB (1 GB)
  • Maximum Execution Duration: 5s (Hobby), 10s (Pro), or 30s (Enterprise)

Now, you can customize these values in your vercel.json file like so:

"functions": {
"api/test.js": {
"memory": 3008,
"maxDuration": 10
An example `vercel.json` file that shows how to customize the `functions` property.

Read more about the constraints for each property in our documentation.

Community Runtimes

When deploying Serverless Functions without configuration (using the /api directory), you can choose from a list of officially supported languages.

If the language you'd like to use is not part of this list, you can add functions to your vercel.json file to assign Community Runtimes to your Serverless Functions.

Community Runtimes are provided by a third-party, for example, vercel-php:

"functions": {
"api/test.php": {
"runtime": "vercel-php@0.0.10"
An example `vercel.json` file that shows how to configure the `vercel-php` Community Runtime.

After configuring the functions property, your api/test.php Serverless Function will be executed using the vercel-php Community Runtime.

If you are interested in using a Community Runtime or creating one yourself, check out the following documentation pages:

API Changes

If you are developing applications on top of the Vercel API, you will need to use v11 of the deployment creation endpoint to take advantage of the functions property.


With the new functions property, you can configure the memory and maximum execution duration of your Serverless Functions, or assign a custom runtime.

Note: The builds property will be deprecated in favor of functions.

This is just one of several features we are planning to launch in order to support advanced use cases of Serverless Functions on Vercel.

Let us know what you think about this change!