Understand Test Agents Settings

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When Calibre synthetic monitoring analyses your Site, it uses a Test Agent. Test Agents run Google Lighthouse with a recent Google Chrome browser version. Changes made to Test Agents are published on our Changelog.

You can customise selected Test Agent settings, such as location, test schedule, custom headers, cookies, and authentication.

Test locations

The Test location option lets you choose one out of 17 global locations, where the Site will be tested from. With multiple available locations, you can ensure the performance of the site is equally good no matter where your audience is.

Test Agent IP addresses

By default, Test Agents use dynamic IP addresses. When using dynamic IP addresses, the IP address of the Test Agent will change between each test. In contrast, fixed IP addresses are the same for each test.

Fixed IPV4 addresses are helpful to allow-list Agent web traffic through firewalls, CDNs, analytics and other security mechanisms.

You can switch between dynamic and fixed IP addresses on a per Site basis. To switch to fixed addresses, visit Site → Synthetic → Settings → Agent IP Address, then select Fixed IP Address and press Save.

Once you switch to fixed IP addresses, the corresponding test location IP address will be displayed. Alternatively, you can view all Agent IP addresses below.

View Agent IP addresses

Location	API LocationTag	IP Address
🇸🇬 Singapore	Singapore	13.229.179.153
🇮🇳 Mumbai, India	Mumbai	52.66.138.107
🇯🇵 Tokyo, Japan	Tokyo	13.115.202.63
🇧🇷 São Paulo, Brazil	SaoPaulo	52.67.68.61
🇰🇷 Seoul, Korea	Seoul	13.125.97.18
🇺🇸 Ohio, USA	Ohio	18.218.2.213
🇺🇸 Oregon, USA	Oregon	34.215.172.173
🇮🇪 Ireland	Ireland	52.212.252.70
🇦🇺 Sydney, Australia	Sydney	54.79.69.167
🇺🇸 Northern California, USA	California	54.177.66.94
🇩🇪 Frankfurt, Germany	Frankfurt	35.156.32.45
🇺🇸 North Virginia, USA	NorthVirginia	52.206.10.99
🇨🇦 Central Canada	Canada	35.182.148.199
🇬🇧 London, United Kingdom	London	35.176.185.182
🇸🇪 Stockholm, Sweden	Stockholm	13.51.34.125
🇿🇦 Cape Town, South Africa	CapeTown	13.244.178.74
🇧🇭 Bahrain	Bahrain	15.184.93.28

Allowing Calibre Test Agents through your WAF

Many websites use a Web Application Firewall (WAF) or bot detection to protect against attacks. To ensure Calibre can successfully test your pages, its Test Agents must have unobstructed access.

You may be blocking Calibre if:

• Tests return a 403 Forbidden HTTP status code.
• Test screenshots show a CAPTCHA or challenge screen.

How to Allowlist Calibre Test Agents

• Set your site’s Test Agent to use a fixed IPv4 address.
• In your WAF console, create a new rule named Calibre Test Agent.
• Set the rule condition to match the IP address shown in Test Agent settings.
• Configure the rule to Allow traffic from this IP.
• After adding the rule, create a new Snapshot in Calibre to confirm access is working.

Authentication

You can configure Test Agent to perform a form-based login to test logged in pages.

HTTP Headers

You can set custom HTTP headers by navigating to Site → Synthetic → Settings → Test Agent. Custom headers are applied to all Site tests.

For more granular setups, you can set custom HTTP headers to Test Profiles.

Cookies

Cookies allow bypassing authentication or turn off specific settings of your Site while testing. When you add a cookie on a Test Agent level, it will be applied to all Test Profiles for the Site.

You can also add cookies to Test Profiles to test specific scenarios.

Common questions

How does Calibre prioritise tests?

Each Calibre test is placed into a regional first-in-first-out queue with a pre-determined priority. Test Agents automatically scale on demand.

Does Calibre run tests with warm cache?

No. Tests are run using a new Chrome user profile (no cache, no prior storage), with no other known network activity, on dedicated hardware.

Is there a HTTP header to identify traffic from Calibre?

No. The best way to identify traffic from Calibre is to add the static, dedicated Test Agent IP addresses to your allow lists and protection mechanisms. Check the Test Agent IP addresses section or use automation (recommended):

1. Agent JSON Endpoint.
2. Calibre’s command line interface has a calibre location-list command.
3. The Node.js API exports a Agent.list() function.