HTTP 412 Precondition Failed — What It Means & How to Fix It

What Does This Error Mean?

A 412 Precondition Failed error means your browser set certain conditions on its request — such as 'only do this if the page has changed' — and the server found those conditions are not met. The server is not broken, and neither is the page. The request just had specific requirements attached that the server could not satisfy. This is a rare error in everyday browsing and usually indicates a website or app configuration issue.

Affected Models

All web browsers
Web applications
File management systems
Caching systems and CDNs

Common Causes

Your browser's cache has an old version of the page with conditions that no longer match
A web application is checking if content was modified before allowing an edit, and it was
A file management system rejected an update because the file version has changed since you opened it
A browser extension added conditional headers that the server does not accept
The website's caching or delivery system has a configuration conflict

How to Fix It

Clear your browser cache completely. Go to Settings > Privacy > Clear browsing data and select 'Cached images and files'.

An old cached version of the page with mismatched conditions is the most common cause.
Close and reopen your browser, then try the page again.

Some browser states persist in memory even after clearing cache. A full restart helps.
Try opening the page in a private or incognito window, which starts with no cache.

If it works in private mode, your regular browser's stored data is the problem.
Disable browser extensions and try again.

Extensions can add conditional request headers that conflict with what the server expects.
If you were editing a shared document and someone else edited it at the same time, reload the document fresh and apply your changes again.

Concurrent edits cause version conflicts that trigger this error in document systems.

When to Call a Professional

Regular visitors rarely encounter this error during normal browsing. If you do, clearing your cache is the best first step. Website owners and developers should review their cache validation logic and conditional request handling.

Frequently Asked Questions

What is a 'precondition' in a web request?

When your browser requests a page, it sometimes adds conditions like 'only send this if the content has changed since I last saw it'. This saves bandwidth. If the condition is not met — for example the content changed in a different way — the server returns a 412.

Is this error dangerous or could I lose data?

The error itself is safe — no data is lost or corrupted. However, if you were trying to save an edit, it may not have been saved. Refresh and check whether your changes were applied.

Will this error fix itself?

Sometimes — if the underlying cached data expires, the conditions reset. Clearing your cache speeds this up considerably.