Why My Large File Edits Kept Failing in Cursor IDE and How I Fixed It

I was deep into a project with a massive 360,000-line code file in Cursor IDE. Then, out of nowhere, every change I tried to apply just stopped working. Each attempt ended with a frustrating red ‘x’. After wrestling with this issue, I found some reliable workarounds that saved my workflow.

The Problem: Why My Edits Kept Failing on Huge Files

Whenever I tried to apply edits in Cursor using the chat or composer at high line numbers — anything above 50,000 — nothing happened. It just canceled with that red ‘x’. In agent mode, it would loop endlessly: apologizing and retrying, but never succeeding.

But when I worked on lower lines or extracted a section to a smaller file? Everything worked fine. That pointed to one clear culprit: a file size limit.

Solutions That Actually Worked

After some trial and error, I found a few fixes that worked for me:

• Use the Diff View Approach: Instead of applying changes directly, I had Composer show me the diffs. Then, I applied those changes manually when the file was open and visible. This avoided the failure.
• Extract to Temporary Files: I copied the code chunk I needed to a new file, made my edits there, and then merged it back. This was perfect for targeted changes.
• Automate with Scripts: To save time, I used tools like sed, awk, or even Python scripts. For example, a simple sed command could update specific lines without relying on Cursor’s apply function.

Switching to models with larger context, like Gemini Pro, sometimes helped a bit. But the core problem? It still stuck around.

Wrapping Up and Looking Ahead

This limitation is tied to AI token constraints. The good news? The Cursor team is actively working on it — either by increasing file size limits or adding better patch logic.

While we wait for those updates, these workarounds have kept me productive. If you’re stuck on a huge file, give them a try!