# How would you investigate a sudden deterioration in Core Web Vitals?

> Establish when the change began.

Then correlate with:

- deployments;

- template changes;

- third-party scripts;

- CDN changes;

- image changes;

- traffic changes;

- device/browser mix.

Compare:

**before vs after**

and:

**affected templates vs unaffected templates**.

Use field data to identify whether the deterioration affects real users and lab tools to reproduce the underlying cause.

## Sources

- [Google Search Central — Core Web Vitals](https://developers.google.com/search/docs/appearance/core-web-vitals)

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Answered by Abhinav Krishna (https://www.theseocentral.com/author/abhinav-krishna)
Source: https://www.theseocentral.com/technical-seo-faq/how-would-you-investigate-a-sudden-deterioration-in-core-web-vitals