table of contents Table of contents

Runtime specification

By default, all our runners have their timezone set to UTC, regardless of their location.

Resource limitations

Each Browser and Multistep check can use up to 3.6GB of memory and 2 CPU cores. This limit applies to all processes spawned by the check, including the browser, the test framework, and the test code itself. The limit is enforced by the runner and is not configurable.

When the memory limit is exceeded, the check will automatically fail with a relevant error message, for example: Your check has reached the maximum memory usage of 3.6GB.

Built-in Node.js modules

  • assert
  • buffer
  • crypto
  • dns
  • fs
  • path
  • querystring
  • readline
  • stream
  • string_decoder
  • timers
  • tls
  • url
  • util
  • zlib

See the built-in module documentation on the official Node.js site:

NPM packages

These are the currently available runtimes and the included external NPM dependencies.

The packages below are included for setup and teardown scripts as well, with the exclusion of Puppeteer, Playwright and Mocha.

We are planning to deprecate mocha in the future. Please use @playwright/test as a test framework instead.


Main updates are Playwright 1.42.1. Node version is 18. New dependencies: @opentelemetry/exporter-metrics-otlp-grpc, @opentelemetry/sdk-metrics, chai-json-schema, pdf2json, protobufjs, long and the nice-grpc family.


Main updates are Playwright 1.38.1 and the addition of ethers 6.7.1, prisma 5.1.1, zod 3.22.2, @t3-oss/env-nextjs 0.6.1 and @xmldom/xmldom 0.8.10. Node version is 18.


Main updates are Playwright 1.32.1, faker 7.6.0 and the addition of date-fns 2.29.3 and ws 8.13.0. We are also dropping support for Mocha.


Main updates are Playwright 1.28.0, Node.js 16.x and Typescript support. We are also dropping support for Puppeteer



This runtime will be available until 2023-12-13. Please update your checks' runtimes and account settings
to avoid failures due to automatic change to the next supported runtime.

Main updates are Playwright 1.20.2 and Puppeteer 13.7.0 and Node.js 14.x

Last updated on March 25, 2024. You can contribute to this documentation by editing this page on Github