Troubleshooting: NimCache Ultra
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# Troubleshooting: NimCache Ultra
**This guide will:** Help you to troubleshoot the cookie error that you've seen with NimCache Ultra.
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**Estimated time to complete:** 4 minutes
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**Background reading:**
* [Guide to: NimCache Ultra (full page caching for WordPress)](https://support.nimbushosting.co.uk/hc/en-gb/articles/7558191613597)
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**Contents:**
* Cache-control headers and cookies
* Troubleshooting
Sometimes caching might not work as expected due to various factors, including cookies. Let's explore how cookies can potentially interfere with NimCache Ultra caching.
### Cache-control headers and cookies:
The Cache-Control header is used to instruct browsers and NimCache Ultra on how to cache a particular resource. If the Cache-Control header includes directives like "private" or "no-cache," it indicates that the resource should not be cached or should be cached only privately for a specific user.
Cookies are often used to store session-related information, and if a resource is marked as private or with a no-cache directive in the Cache-Control header, NGINX might honour these instructions to bypass caching for that resource.
#### **Troubleshooting:**
To address these issues and allow NimCache Ultra to work effectively, you might need to:
* Ensure that your website server is not sending a "Vary: Cookie" header if it's unnecessary
* Check and adjust Cache-Control headers to permit caching when appropriate, even if cookies are present.
Either of these could be set by a third-party WordPress plugin. We recommend disabling all plugins to see if this resolves it. If it does then enable each plugin one by one until you find the offending plugin.
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Still having issues? [Raise a ticket](nim.host/ticket)
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**Further reading:**
* [Guide to: NimCache Ultra (full page caching for WordPress)](https://support.nimbushosting.co.uk/hc/en-gb/articles/7558191613597)
Updated 15 days ago