What is local storage and how do websites use it?

Local storage lets websites save data directly in your browser so it persists between visits. Learn how it works, what websites use it for, and what it means for your site.

Have you ever set a preference on a website, closed the tab, and come back later to find everything exactly as you left it? Your display settings were still the same, your saved items were still there, and you did not have to set anything up again. That is local storage quietly doing its job in the background.

In the previous chapter on types of browser storage, we introduced local storage as one of the main ways browsers hold onto data. This chapter goes deeper into what local storage actually is, how it works, and what role it plays on your website.

What is local storage?

Local storage is a type of browser storage that allows websites to save small pieces of data directly on a visitor's device. That data stays in the browser even after the visitor closes the tab or shuts down their computer. The next time they visit the same website, the browser still has that data available and the site can use it to restore their previous state.

This is what makes local storage different from session storage, which clears when the tab closes. Local storage is persistent. It does not have an automatic expiry. The data stays until the user clears their browser, or until the website itself removes it.

How does local storage work?

Local storage works as a simple key-value store. Think of it like a small notepad inside the browser where a website can write down information using a label and a value. The label is the key and the information saved under it is the value. When the website needs that information again, it looks up the key and retrieves the value.

For example, a website might save a key called "theme" with a value of "dark" when a visitor switches to dark mode. The next time that visitor comes back, the website checks local storage, finds the "theme" key, reads the value "dark," and applies the dark mode automatically before the page even fully renders.

Each website gets its own isolated local storage. A website can only read and write its own data. It cannot see what any other website has stored. This isolation is a security feature built into every browser.

What do websites use local storage for?

Saving user preferences

Display settings, language preferences, theme choices, and layout options are all common things stored in local storage. These are non-sensitive preferences that improve the experience when a visitor returns.

Keeping items between sessions

Some websites use local storage to hold items that a visitor has interacted with, like a reading list, a wishlist, or recently viewed items, so they are still there on the next visit even if the visitor is not logged in.

Reducing server requests

When a website stores information locally, it can retrieve it instantly from the browser instead of making a request to the server every time. This speeds up the experience for returning visitors and reduces load on the backend.

Keeping state in forms and multi-step processes

Some websites use local storage to temporarily save progress in a multi-step form or checkout flow. If a visitor accidentally closes the tab, their progress is not lost when they come back.

What are the limits of local storage?

Local storage is designed for small data. Most browsers allow around 5 to 10 megabytes per website, which is plenty for preferences and settings but not for large files or complex datasets. It also only stores text. Numbers, objects, and arrays need to be converted to text first before they can be saved and converted back when retrieved.

Local storage is also not the right place for sensitive information. Because it is accessible to any script running on the page, storing passwords, personal details, or payment information in local storage is a security risk. Sensitive data belongs on the server, protected by SSL and proper authentication.

For a side-by-side comparison of how local storage compares to the other storage types, read types of browser storage.

Frequently asked questions