Test Profiles

Test Profiles allow you to change the conditions that your site is tested under. Calibre can emulate popular devices (like iPhones, iPads and Nexus phones), throttle network connectivity, set custom headers or cookies, block ads or the execution of JavaScript.

Test Profiles can be found for each site in Calibre by navigating to Site → Settings → Test Profiles.

Test Profile list and creation screen

Default Test Profiles

When you add Sites, Calibre creates three default Test Profiles automatically:

NameDevice EmulationConnection SpeedComment
Chrome DesktopNo device emulation. 1280×1024 px screen dimensions.CableDesktop-class, full-screen browser.
MotoG4, 3G connectionMotorola Moto G4. 360×640 px screen dimensions.Regular 3GA representative of an average global phone with global average mobile connectivity.
iPhone, 4G LTEApple iPhone 8. 375x667 px screen dimensions.4G LTEA fast phone with world-leading mobile connectivity.

Device Emulation

We leverage Google Chrome device emulation with a few additional mechanisms to ensure that the experience is as close to a real device as possible.

Calibre can emulate the following devices:

  • Motorola Moto G4
  • iPhone 5
  • iPhone 6
  • iPhone 6 Plus
  • iPhone 7
  • iPhone 8
  • Nexus 5X
  • Nexus 6P
  • Galaxy S5
  • iPad
  • iPad Pro

When Calibre emulates a device, the following occurs:

  • The device viewport is changed.
  • The User-Agent is set to that of the device.
  • The CPU will be slowed to reflect the hardware conditions of the device.

Emulated Network Connection Speed

Calibre limits the bandwidth available to the browser by using pre-configured network speed options that best reflect average global connectivity.

Those pre-configured options are:

No bandwidth throttling
Regular 2G300ms256 KB/s51.2 KB/s
Good 2G150ms460.80 KB/s153.60 KB/s
Slow 3G400ms320 KB/s320 KB/s
Regular 3G300ms768 KB/s256 KB/s
Good 3G150ms1.57 MB/s768 KB/s
Emerging markets 3G400ms3.2 MB/s3.2 MB/s
Regular 4G170ms12.19 MB/s3.15 MB/s
4G LTE70ms24 MB/s24 MB/s
DSL30ms2.10 MB/s1.05 MB/s
WiFi10ms31.46 MB/s15.73 MB/s
Cable20ms40 MB/s40 MB/s


Setting custom cookies can be helpful in a variety of scenarios. The most common implementations include:

  • Authenticating Calibre to your web application.
  • Disabling advertising to ease troubleshooting of developer-specific regressions.
  • Testing against an A/B test or staff-shipped feature.


Custom headers are useful for setting Authorisation headers for basic authentication or for triggering certain conditions for your Pages.

Blocking ads

Advertising often has a significant impact on site speed. When creating a Test Profile, select “Block ads” to analyze the impact on speed and accessibility. Calibre’s ad blocking feature is powered by uBlock.

Blocking third party scripts

Calibre automatically detects third party providers during testing, based on a custom instance of Third Party Web dataset. When creating or editing a Test Profile, choose which providers you would like to the requests will be blocked when Snapshots run.

Each provider is listed with a Last Detected date. Some of the registered third parties can no longer be present on your Site but were included in the past. When blocking, make sure to include active third parties for reliable results.

A list of all detected third parties in Test Profile creation flow

We recommend experimenting with disabling:

  • Chat widgets and communication tools.
  • Scripts providing polyfills.
  • Analytics software.
  • Bug tracking scripts.

Blocking JavaScript

Turning off JavaScript is an excellent strategy in discovering potential functionality and accessibility issues when JavaScript execution fails or is not reliable.

When creating or editing a Test Profile, select “Block JavaScript Requests” to ignore all external JavaScript requests. When JavaScript is blocked, all requests except inline script (<script>my script</script>) included on the page will be halted.

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