The Tool Desk
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Choose the image for your browser, not just its size
Cypress documents four main image families. Their contents determine how much you need to install and maintain yourself. The exact tags, Node versions, browser versions, and architecture coverage change, so check the current Cypress CI documentation and the image registry before pinning a tag. Do not assume every browser is available on every architecture.
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| Image family | What it includes | When it fits |
|---|---|---|
cypress/base |
Debian, Cypress prerequisites, Node.js, npm, and Yarn v1 | Consider it when you need the base environment and your browser requirements are limited. Verify the browser behavior your tests require before adopting it. |
cypress/browsers |
The base image plus installed browsers | Use it when tests need an installed Chrome, Firefox, or Edge version; confirm the required browser, Node version, tag, and platform are available together. |
cypress/included |
The browser image plus a globally installed, fixed Cypress version | Convenient when the included Cypress and browser combination matches your project. It is not automatically the leanest choice if you need a different combination. |
cypress/factory |
A base used to generate customized images with selected components | Useful when published combinations do not fit, provided you can maintain and validate the resulting dependencies. |
If your tests use headless Electron and do not require a separately installed Chrome, Firefox, or Edge, investigate whether a leaner suitable image family can meet the requirement. Do not strip libraries simply to save bytes: validate the exact Cypress and browser combination. Official Cypress images include required dependencies; an arbitrary custom Linux base does not inherit that guarantee.
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There is no universal smallest Dockerfile or image tag that is fastest for every project. First select a currently documented image tag matching your required Node and browser versions, and verify its platform support. Pin that tag in your repository rather than relying on a moving tag. Then run tests with the project lockfile and the same browser mode used in CI.
- Record requirements: identify the Cypress version, Node version, browser and version, and CI architecture your suite needs.
- Select a matching image: check the current Cypress Docker image documentation and registry for a compatible tag. If no published combination fits, use the factory/custom-image route or build from a supported Linux base and install documented prerequisites.
- Install reproducibly: commit the npm lockfile and use
npm ci. For Yarn, use its frozen-lockfile installation mode. - Measure the actual result: compare final image size, build and pull time, cache hits, and test duration on the CI runner you use.
Because image tags and combinations are version-sensitive, avoid copying an unverified tag from an old example. Once chosen, keep the tag pinned and update it deliberately alongside the browser and Cypress versions.
Cut repeated installation time with CI caches
Cypress consists of an npm package and a separate platform-specific binary. Cypress’s performance documentation describes that binary as over 100 MB; that is a stated binary size, not a Docker image-size measurement. On Linux, the binary cache is ~/.cache/Cypress. Persist it between CI runs, along with the package manager’s own cache, to avoid repeated downloads.
- Key caches to the lockfile and relevant Cypress version so dependency changes invalidate stale entries.
- Do not cache
node_modulesdirectly. Cypress warns that doing so can bypass integrity checks and the binary download performed by its postinstall process. - Avoid broad cache keys that allow obsolete Cypress binaries to accumulate.
- Cypress says its GitHub Action handles npm and Cypress binary caching automatically; confirm the current action version and workflow configuration before relying on that behavior.
Caching reduces setup work; it does not shorten the time a test itself takes. A cold-cache run and a warm-cache run can differ substantially in setup time, so track both if CI performance is important.
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Reduce suite time before adding more runners
Find the slowest tests and setup steps first. Cypress’s published duration guidance—not an independent benchmark of your project—categorizes individual end-to-end tests under three seconds as excellent, three to ten seconds as acceptable for many tests against a real server, ten to thirty seconds as worth investigating, and over thirty seconds as poor. Component tests should consistently run under two seconds.
- Inspect slow tests for unnecessary waits, repeated setup, and slow application or test-server behavior.
- Check whether one spec file is much longer than the rest; a single long file can constrain parallel work.
- Observe CPU and memory use on the runner. Saturated machines may not benefit from additional browser processes.
- Separate image build/pull and dependency-install time from browser startup and test execution when identifying the bottleneck.
Parallelize specs when recorded runs fit your workflow
Cypress Cloud can distribute whole spec files across multiple CI machines for recorded runs. This requires a recorded run (including --record) and specs split across files; it does not make one individual test intrinsically faster. Similar-duration specs help keep machines busy, while one unusually long spec can leave other runners idle.
Cypress’s performance guide gives an illustrative Kitchen Sink example: a 1:51 serial run became 59 seconds with a second machine, a 53% reduction. That is Cypress’s example, not a promised speedup for another suite. Browser launch and video-encoding overhead can limit further gains, and extra runners add cost. Compare elapsed-time savings with runner charges and inspect spec balance before scaling out.
Troubleshoot common slowdowns
- The job downloads Cypress on every run: persist Linux’s
~/.cache/Cypressand the package-manager cache; check the cache key and restore path. - The cached binary does not match the install: narrow cache keys to the lockfile and Cypress version, and remove stale cache entries rather than using a broad key.
- Install behavior is inconsistent: use the committed lockfile with
npm ci(or Yarn’s frozen-lockfile mode); do not restorenode_modulesas a substitute. - A browser fails to launch in a custom image: verify the selected tag, architecture, browser availability, and system prerequisites. Cypress’s official images include required dependencies; a custom base needs you to provide and maintain them.
- Parallel CI barely improves elapsed time: check that the run is recorded, specs are split into files of reasonably similar duration, and browser/video overhead or runner saturation is not dominating.
- The image is small but CI is still slow: measure pull/build time separately from install and test time. Then optimize the stage that actually consumes the time.
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Frequently Asked Questions
Does a smaller Docker image make Cypress tests faster?
Not necessarily. It can reduce image build or pull time, but test duration depends on the suite and runner. Measure those stages separately.
Does Cypress parallelization work on a single spec file?
Cypress Cloud parallelizes whole spec files across machines, so a suite needs multiple spec files to distribute work.
Quick Recap
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