---
title: "Store each preference where it is needed · Agent Wranglers"
url: https://agentwranglers.se/playbook/website/privacy/preference-storage
updated: 2026-10-20
licence: "All rights reserved"
---

# Store each preference where it is needed

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

- Level: Recommended
- Chapter: [Privacy](https://agentwranglers.se/playbook/website/privacy)
- Rule: Keep a visitor's preferences in local storage when only the browser needs them. Use a cookie only when the server must know the preference before it answers.
- How: Local storage stays on the device and is never sent with requests. A theme or a dismissed notice belongs there, read by a tiny script in the head before the first paint. A cookie travels with every request, so the server can send the right language or currency at once. Give such a cookie `Secure`, `SameSite=Lax` and no longer a life than the preference needs. Under EU rules, storage the visitor asked for is usually exempt from consent, but say it in the privacy policy. Never set a cookie only for your own scripts to read. Wrap storage in `try`, because private windows can block it.
- Check: Set the preference and reload. It shows at once with no flash, and requests carry no cookie unless the server reads it.

Example:

| Question | Local storage | Cookie |
| --- | --- | --- |
| Sent to the server? | Never | With every request |
| Server can use it for the first response? | No | Yes |
| Read before first paint? | Yes, from an inline script | Yes, by the server |
| Size | About 5 MB per site | About 4 KB each |
| Good for | Theme, layout, dismissed notices | Language, currency, region |

```html
<!-- Local storage: applied before the first paint, never leaves the device -->
<script>try { const t = localStorage.getItem("theme"); if (t) document.documentElement.dataset.theme = t } catch (e) {}</script>
```

```http
Set-Cookie: lang=sv; Path=/; Max-Age=31536000; Secure; SameSite=Lax
```

**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/privacy/preference-storage`.

- Previous: [Keep only what you need and delete it on time](https://agentwranglers.se/playbook/website/privacy/data-minimization)
- Next: [Keep personal data out of addresses](https://agentwranglers.se/playbook/website/privacy/personal-data-out-of-urls)
- [Privacy](https://agentwranglers.se/playbook/website/privacy)