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# Srsltid impacting Core Web Vitals via TTFB caching

The srsltid auto-tracking parameter already caused SEO havoc amongst site owners using Google Merchant Center. But issues aren't stopping there.

The `srsltid` URL parameter is added for Merchant Center "auto-tagging" as described by [this Google support page](https://support.google.com/merchants/answer/15191080). It's only added when a site-owner has activated that feature. They're used for conversion tracking for merchants.  
  
They're added in search directly, with unique IDs using the `srsltid` URL parameter. [At RUMvision, we started noticing](https://www.linkedin.com/posts/erwinhofman_seo-corewebvitals-activity-7245374876671250433-EQeK) that 5% to sometimes even 17% of pagehits include this new `srsltid` URL parameter.

## srsltid solutions

In general, the following solutions have been proposed by SEO blogs to combat issues with `srsltid` parameter:

- **disable srsltid**  
    Deselecting auto-tagging option in Merchant Center Conversion Settings. Do note this results in losing performance tracking of free listings through Google Merchant Center.
- **canonical tag**  
    adding canonical metatags to your pages that excludes query strings that could result in duplicate content (if you haven't done this yet)
 
However, according to John Mueller (Search Advocate at Google), this parameter should not have an impact on crawling, indexing, or rankings.

> This doesn't affect crawling, indexing, or ranking - it's basically just for analytics for merchants  
> [John Mueller on LinkedIn](https://www.linkedin.com/feed/update/urn:li:ugcPost:7222171975031386112?commentUrn=urn%3Ali%3Acomment%3A%28ugcPost%3A7222171975031386112%2C7230136034133487616%29&dashCommentUrn=urn%3Ali%3Afsd_comment%3A%287230136034133487616%2Curn%3Ali%3AugcPost%3A7222171975031386112%29)

## Impact on Core Web Vitals

RUMvision data is showing that this statement isn't fully true. That's because the `srsltid` parameter is new to many site owners. Because of this, many site owners and hosting companies haven’t added this (or other newly introduced parameters) to their caching strategy.

As a result, caching layers won't recognize this parameter and won't apply their caching mechanisms. This leads to users visiting pages that need to be fully generated by platforms like Magento or Shopify.

### Increased TTFB

This then leads to a higher server response time, which will directly increase the Time to First Byte (TTFB) metric. You might recognize this as we wrote about this before in regards of [Google Ads impacting Core Web Vitals](https://www.rumvision.com/blog/google-ads-impacting-core-web-vitals/?format=md).

The following screenshot of a merchant using RUMvision is confirming the impact on the TTFB metric at the 75th percentile across all browsers on mobile devices:

[![srsltid-parameter-ttfb-impact.png](https://www.rumvision.com/file/upload/img/srsltid-parameter-ttfb-impact.png)](https://www.rumvision.com/file/upload/img/srsltid-parameter-ttfb-impact.png)

In this example of a real shop, we can see that the `srsltid` parameter is 111.8% worse than the overall TTFB. And even more so when comparing a **1417 ms TTFB** with the **302 ms TTFB** that could have been achieved using a proper caching strategy.

And when TTFB regresses, the First Contentful Paint (FCP) and [Largest Contentful Paint (LCP)](https://www.rumvision.com/blog/how-to-fix-largest-contentful-paint/?format=md) will regress as well.

### Page Experience ranking signal

While TTFB is not a Core Web Vitals metric itself, it has a significant downstream impact on Largest Contentful Paint (LCP), which is [part of Core Web Vitals](https://web.dev/articles/vitals#core-web-vitals). As Core Web Vitals is part of the [Page Experience ranking signal](https://www.rumvision.com/help-center/glossary/other/page-experience-ranking-signal/?format=md), this new parameter is in fact likely to impact your SEO ranking.

## Mitigating the impact on Core Web Vitals

This means you would want to prevent the `srsltid` URL parameter from impacting your Core Web Vitals. Continuous pagespeed monitoring is the solution here.

### Real User Monitoring

Real User Monitoring (RUM) in particular is the solution here, as RUM will expose new conditions you weren't aware of before. This includes new URL parameters like `srsltid`. Obviously, RUMvision is such a solution that individually tracks the impact for each URL parameter combination.

This will help site owners to compare such list with their caching strategy and properly [align their caching rules](https://www.rumvision.com/blog/make-sure-to-check-your-caching-rules/?format=md). TTFB should then restore, improving FCP and LCP metrics at the same time.

### Announcement by RUMvision

Our data was showing that multiple site owners using RUMvision were impacted by this new `srsltid `parameter. As a result, RUMvision users have already received a detailed mail to actively inform them, including necessary steps to mitigate the impact.