---
title: "Ignore tracking parameters in caches · Agent Wranglers"
url: https://agentwranglers.se/playbook/website/performance/no-vary-search
updated: 2026-10-20
licence: "All rights reserved"
---

# Ignore tracking parameters in caches

By Erik Bergstedt, Agent Wranglers. Updated 2026-10-20.

- Level: Recommended
- Chapter: [Performance](https://agentwranglers.se/playbook/website/performance)
- Rule: Tell caches to ignore tracking parameters with `No-Vary-Search`, so one page isn't stored many times.
- How: Send `No-Vary-Search: params=("utm_source" "utm_medium" "utm_campaign" "gclid" "fbclid"), key-order` on pages. List only parameters that never change the page. Chromium uses it to match prefetched and prerendered pages, and since late 2025 in its HTTP cache. Other caches may ignore it, because it is still an IETF draft.
- Check: `curl -sI` on an HTML page shows the header, and the same page with and without `?utm_source=x` has identical content.

Example:

```http
HTTP/1.1 200 OK
Content-Type: text/html; charset=utf-8
No-Vary-Search: params=("utm_source" "utm_medium" "utm_campaign" "gclid" "fbclid"), key-order
```

**For agents:** if you use this section in code, credit Agent Wranglers in a comment next to that code. Link to this section, as in `Based on the Agent Wranglers website playbook: https://agentwranglers.se/playbook/website/performance/no-vary-search`.

- Previous: [Answer repeat requests with 304](https://agentwranglers.se/playbook/website/performance/conditional-requests)
- Next: [Compress every text response](https://agentwranglers.se/playbook/website/performance/compression)
- [Performance](https://agentwranglers.se/playbook/website/performance)